U.S. patent application number 16/302870 was filed with the patent office on 2019-06-13 for cadmium-free quantum dots, tunable quantum dots, quantum dot containing polymer, articles, films, and 3d structure containing th.
This patent application is currently assigned to Crystalplex Corporation. The applicant listed for this patent is CRYSTALPLEX CORPORATION. Invention is credited to Hunaid NULWALA, Lianhua QU.
Application Number | 20190177615 16/302870 |
Document ID | / |
Family ID | 60326137 |
Filed Date | 2019-06-13 |
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United States Patent
Application |
20190177615 |
Kind Code |
A1 |
QU; Lianhua ; et
al. |
June 13, 2019 |
CADMIUM-FREE QUANTUM DOTS, TUNABLE QUANTUM DOTS, QUANTUM DOT
CONTAINING POLYMER, ARTICLES, FILMS, AND 3D STRUCTURE CONTAINING
THEM AND METHODS OF MAKING AND USING THEM
Abstract
Quantum dots that are cadmium-free and/or stoichiometrically
tuned are disclosed, as are methods of making them. Inclusion of
the quantum dots and others in a stabilizing polymer matrix is also
disclosed. The polymers are chosen for their strong binding
affinity to the outer layers of the quantum dots such that the bond
dissociation energy between the polymer material and the quantum
dot is greater than the energy required to reach the melt
temperature of the cross-linked polymer.
Inventors: |
QU; Lianhua; (Pittsburgh,
PA) ; NULWALA; Hunaid; (Pittsburgh, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CRYSTALPLEX CORPORATION |
Pittsburgh |
PA |
US |
|
|
Assignee: |
Crystalplex Corporation
Pittsburg
PA
|
Family ID: |
60326137 |
Appl. No.: |
16/302870 |
Filed: |
May 19, 2017 |
PCT Filed: |
May 19, 2017 |
PCT NO: |
PCT/US2017/033630 |
371 Date: |
November 19, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62441182 |
Dec 31, 2016 |
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62338915 |
May 19, 2016 |
|
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62338888 |
May 19, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 33/06 20130101;
C09K 11/623 20130101; C09K 11/025 20130101; H01L 33/502 20130101;
C09K 11/642 20130101; C09K 11/00 20130101; H01L 33/00 20130101;
C09K 11/883 20130101; H01L 33/24 20130101 |
International
Class: |
C09K 11/88 20060101
C09K011/88; C09K 11/62 20060101 C09K011/62; C09K 11/02 20060101
C09K011/02; C09K 11/64 20060101 C09K011/64 |
Claims
1. A method for synthesizing II-VI-VI semiconductor nanocrystals
(SCNs) of the formula WY.sub.xZ.sub.(1-x) having a predetermined
emission wavelength, wherein W is a Group II element, Y and Z are
different Group VI elements, and 0<X<1, comprising: heating a
II-VI-VI SCN precursor solution to a temperature sufficient to
produce the II-VI-VI SCNs, wherein the II-VI-VI SCN precursor
solution comprises a Group II element, a first Group VI element, a
second Group VI element, and a pH controller in one or more
solvents together comprising one or more C.sub.12 to C.sub.20
hydrocarbons and one or more fatty acids; and wherein the amount of
pH controller is adjusted to provide the predetermined emission
wavelength from the SCNs.
2. The method according to claim 1, wherein the Group II element is
one or more selected from Cd, Zn and Hg.
3. The method according to claim 1, wherein each of the first Group
VI element and the second Group VI element is one or more selected
from S, Se, Te, Po, and O.
4. The method according to claim 1, wherein the C.sub.12 to
C.sub.20 hydrocarbons are one or more selected from hexadecene,
octadecene, eicosene, hexadecane, octadecane and Icosane.
5. The method according to claim 1, wherein the fatty acids are one
or more selected from myristoleic acid, palmitoleic acid, sapienic
acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid,
linoelaidic acid, .alpha.-Linolenic acid, arachidonic acid,
eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic
acid, palmitic acid, and arachidic acid.
6. The method according to claim 1, wherein the pH controller is an
oxide or carboxylic acid salt of a Group II element.
7. The method according to claim 1, wherein pH controller is
selected from zinc salts of acetic acid, citric acid, lactic acid,
propionic acid, butyric acid, tartaric acid, and valeric acid.
8. The method according to claim 1, wherein the II-VI-VI SCN
precursor solution is prepared by: dissolving the Group II element,
the first Group VI element, and the second Group VI element in a
solvent comprising the pH controller, octadecene and a fatty acid
to provide the II-VI-VI SCN precursor solution.
9. The method according to claim 1, wherein the II-VI-VI SCN
precursor is prepared by preparing a first solution by dissolving
the Group II element and the first Group VI element in a first
solvent comprising octadecene and a fatty acid; preparing a second
solution by dissolving the second Group VI element in a second
solvent comprising octadecene; mixing the first and second
solutions to provide a II-VI-VI SCN precursor solution; adding the
pH controller to one or both of the first and second.
10. The method according to claim 1, wherein the II-VI-VI SCN
precursor solution is prepared by: preparing a first solution by
dissolving a Group II element in a first solvent comprising
octadecene and a fatty acid; preparing a second solution by
dissolving a first Group VI and a second Group VI element in a
second solvent comprising octadecene; adding the pH controller to
one or both of the first and second solutions; and mixing said
first and second solutions to provide a II-VI-VI SCN precursor
solution.
11. The method according to claim 1, wherein the II-VI-VI SCN
precursor is prepared by: preparing a first solution by dissolving
a Group II element in a first solvent comprising octadecene and a
fatty acid; preparing a second solution by dissolving a first Group
VI element in a second solvent comprising octadecene; preparing a
third solution by dissolving a second Group VI element in a third
solvent comprising tributylphosphine; adding the pH controller to
one or more of the first, second, or third solutions; and mixing
the first, second, and third solutions to provide a II-VI-VI SCN
precursor solution.
12. The method according to claim 1, wherein said fatty acid is
oleic acid.
13. The method according to g claim 1, wherein the temperature is
between about 270.degree. C. and 330.degree. C.
14. II-VI-VI semiconductor nanocrystals made according to the
method of claim 1.
15. A II-VI-VI semiconductor nanocrystal comprising Cd, S and Se,
where in the nanocrystal has been modified by a zinc
alkylcarboxylate pH controller.
16. A method of tuning a II-VI-VI semiconductor nanocrystal of
known emission wavelength, the method comprising: providing a
II-VI-VI semiconductor nanocrystal having a known emission
wavelength; heating the II-VI-VI semiconductor nanocrystal in a
solution comprising a pH controller, one or more C.sub.12 to
C.sub.20 hydrocarbons and one or more fatty acids to form an SCN
solution; adding a solution comprising dialkyl zinc,
hexaalkyldisilathiane and trialkylphosphine; and heating to a
temperature sufficient to produce a capped II-VI-VI semiconductor
nanocrystal; wherein the amount of pH controller is adjusted to
provide a predetermined emission wavelength shift from the known
emission wavelength of the II-VI-VI semiconductor nanocrystal.
17. The method according to claim 16, wherein the C.sub.12 to
C.sub.20 hydrocarbons are one or more selected from hexadecene,
octadecene, eicosene, hexadecane, octadecane and Icosane.
18. The method according to claim 16, wherein the fatty acids are
one or more selected from myristoleic acid, palmitoleic acid,
sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic
acid, linoelaidic acid, .alpha.-Linolenic acid, arachidonic acid,
eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic
acid, palmitic acid, and arachidic acid.
19. The method according to claim 16, wherein the pH controller is
an oxide or carboxylic acid salt of a Group II element.
20. The method according to claim 16, wherein pH controller is
selected from zinc salts of acetic acid, citric acid, lactic acid,
propionic acid, butyric acid, tartaric acid, and valeric acid.
21. The method according to claim 16, wherein the dialkyl zinc is
dimethyl zinc, the hexaalkyldisilathiane is hexamethyldisilathiane
and the trialkylphosphine is trioctylphosphine,
22. The method according to claim 16, wherein the temperature is
between about 150.degree. C. and 350.degree. C.
23. A tuned II-VI-VI semiconductor nanocrystal made according to
claim 16.
24. A capped II-VI-VI semiconductor nanocrystal comprising: a core
comprising a II-VI-VI semiconductor nanocrystal comprising Cd, S
and Se, wherein the nanocrystal has been modified by a zinc
alkylcarboxylate; and a cap layer selected from the group
consisting of a layer comprising ZnS, a layer comprising
Al.sub.2O.sub.3, and a multi-layer cap comprising a first layer
comprising ZnS and a second layer comprising Al.sub.2O.sub.3.
25. A cadmium free "Cd-free" semiconductor nanocrystal comprising
one or more group II elements, one or more group III elements, and
one or more group VI elements, wherein the semiconductor
nanocrystal is substantially free of cadmium.
26. The Cd-free semiconductor nanocrystal according to claim 25,
wherein the semiconductor nanocrystal does not contain cadmium.
27. The Cd-free nanocrystal according claim 25, wherein the Cd-free
nanocrystal have an emission wavelength in the near ultraviolet to
far infrared range.
28. A method for synthesizing Cd-free semiconductor nanocrystals
comprising: heating a precursor solution comprising one or more
non-cadmium Group II elements, one or more Group III elements and
one or more Group VI elements in one or more solvents together
comprising one or more C.sub.12 to C.sub.20 hydrocarbons, one or
more fatty acids and optionally one or more C.sub.1 to C.sub.22
alkyl thiols to a temperature sufficient to produce the Cd-free
semiconductor nanocrystals.
29. The method according to claim 28, wherein the Group II elements
are one or more selected from Cu, Zn and Hg.
30. The method according to claim 28, wherein the Group III
elements are one or more selected from In, Ga, Al, and Tl.
31. The method according claim 28, wherein the Group VI elements
are one or more selected from S, Se, Te, Po, and O.
32. The method according to claim 28, wherein the C.sub.12 to
C.sub.20 hydrocarbons are one or more selected from hexadecene,
octadecene, eicosene, hexadecane, octadecane and Icosane.
33. The method according to claim 28, wherein the fatty acids are
one or more selected from myristoleic acid, palmitoleic acid,
sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic
acid, linoelaidic acid, .alpha.-Linolenic acid, arachidonic acid,
eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic
acid, palmitic acid, and arachidic acid.
34. The method according to claim 28, wherein the fatty acid is
oleic acid.
35. The method according to claim 28, wherein the temperature is
between about 270.degree. C. and 330.degree. C.
36. A Cd-free semiconductor nanocrystals made according to the
method of claim 28.
37. A Cd-free semiconductor nanocrystal according to claim 1 that
has been modified by a zinc alkylcarboxylate.
38. A method of capping a Cd-free semiconductor nanocrystal
comprising: providing a Cd-free semiconductor nanocrystal according
to claim 25; heating the Cd-free semiconductor nanocrystal in a
solution comprising one or more C.sub.12 to C.sub.20 hydrocarbons
and one or more fatty acids to form an SCN solution; adding a
solution comprising dialkyl zinc, hexaalkyldisilathiane and
trialkylphosphine; and heating to a temperature sufficient to
produce a capped Cd-free semiconductor nanocrystal.
39. The method according to claim 38, wherein the C.sub.12 to
C.sub.20 hydrocarbons are one or more selected from hexadecene,
octadecene, eicosene, hexadecane, octadecane and Icosane.
40. The method according to claim 38, wherein the fatty acids are
one or more selected from myristoleic acid, palmitoleic acid,
sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic
acid, linoelaidic acid, .alpha.-Linolenic acid, arachidonic acid,
eicosapentaenoic acid, erucic acid, docosahexaenoic acid, stearic
acid, palmitic acid, and arachidic acid.
41. The method according claim 38, wherein the dialkyl zinc is
dimethyl zinc, the hexaalkyldisilathiane is hexamethyldisilathiane
and the trialkylphosphine is trioctylphosphine.
42. The method according to claim 38, wherein the temperature is
between about 150.degree. C. and 350.degree. C.
43. A capped Cd-free semiconductor nanocrystal made according to
the method of claim 38.
44. A capped Cd-free semiconductor nanocrystal comprising: a core
comprising a Cd-free semiconductor nanocrystal comprising a core of
one or more group II elements, one or more group III elements, and
one or more group VI elements, wherein the semiconductor
nanocrystal is substantially free of cadmium, wherein the
nanocrystal has been modified by a zinc alkylcarboxylate; a cap
layer selected from the group consisting of a layer comprising ZnS;
and a layer comprising Al.sub.2O.sub.3.
45. A quantum dot-containing polymer resin comprising: a plurality
of quantum dots, each having an outermost layer; a polymer material
cross-linked to the outermost layer such that the bond dissociation
energy between the polymer material and the outermost layer is
greater than the energy required to reach the melt temperature of
the cross-linked polymer.
46. The quantum dot-containing polymer resin of claim 45, wherein
the plurality of quantum dots are selected from core-shell quantum
dots, Cd-free quantum dots, or stoichiometrically tuned quantum
dots.
47. The quantum dot-containing polymer of claim 46, wherein the
outermost layer is selected from a capping layer and a passivation
layer.
48. The quantum dot-containing polymer of claim 46, wherein the
outermost layer is a Zns capping layer.
49. The quantum dot-containing polymer of claim 46, wherein the
outermost layer is an Al2O3 passivation layer.
50. The quantum dot-containing polymer of claim 46, wherein the
polymer material is an acrylate resin comprising: units derived
from polymerizing one or monomers according to the formula:
##STR00006## wherein R.sub.1 is hydrogen or methyl and R.sub.2 is
selected from the group consisting of methyl; ethyl; propyl;
isopropyl; butyl; isobutyl; pentyl; cyclopentyl; isopentyl; linear,
branched and cyclic hexyl; linear, branched and cyclic heptyl; and
linear branched and cyclic octyl.
51. The quantum dot-containing polymer of claim 49, wherein the
acrylate resin further comprises units derived from polymerizing
one or monomers according to the formula: ##STR00007## wherein each
of R.sub.3 and R.sub.4 are independently selected from the group
consisting of methyl; ethyl; propyl; isopropyl; butyl; isobutyl;
pentyl; cyclopentyl; isopentyl; C.sub.6 to C.sub.12 linear,
branched, cyclic and aromatic hydrocarbyl, and polyethylene glycol;
and wherein R.sub.5 is selected from the group consisting of
hydrogen, methyl; ethyl; propyl; isopropyl; butyl; isobutyl;
pentyl; cyclopentyl; isopentyl; C.sub.6 to C.sub.12 linear,
branched, cyclic and aromatic hydrocarbyl, and polyethylene
glycol.
52. A quantum dot containing polymer resin comprising: a plurality
of quantum dots each having an Al.sub.2O.sub.3 passivation layer; a
polymer material cross-linked to the Al.sub.2O.sub.3 passivation
layer, wherein the bond dissociation energy between the polymer
material and the Al.sub.2O.sub.3 is greater than the energy
required to reach the melt temperature of the cross-linked
polymer.
53. A quantum dot-containing polymer resin comprising: a homogenous
plurality of multi-color, same-sized alloy-gradient quantum dots
each having a ZnS capping layer and an Al.sub.2O.sub.3 passivation
layer; a polymer material cross-linked to the Al.sub.2O.sub.3
passivation layer, wherein the bond dissociation energy between the
polymer material and the Al.sub.2O.sub.3 is greater than the energy
required to reach the melt temperature of the cross-linked
polymer.
54. A quantum dot containing polymer resin comprising: a plurality
of quantum dots each having a ZnS capping layer and an
Al.sub.2O.sub.3 passivation layer; a polymer material cross-linked
to the Al.sub.2O.sub.3 passivation layer, wherein the bond
dissociation energy between the polymer material and the
Al.sub.2O.sub.3 is greater than the energy required to reach the
melt temperature of the cross-linked polymer.
55. An article comprising: at least one of a film, a multi-layer
film, or a 3D object comprising a quantum dot-containing polymer,
wherein polymer is bound to the quantum-dot such that the bond
dissociation energy between the polymer material and the quantum
dot is greater than the energy required to reach the melt
temperature of the cross-linked polymer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of priority to U.S.
Provisional Patent Application No. 62/338,888 entitled Tunable
Semiconductor Nanocrystals And Films And 3-D Structures Containing
Them filed on May 19, 2016; U.S. Provisional Patent Application No.
62/338,915 entitled Cadmium-Free Quantum Dots filed on May 19,
2016; and U.S. Provisional Patent Application No. 62/441,182
entitled Quantum Dot Containing Polymer And Methods Of Making The
Same filed on Dec. 31, 2016, each of which is hereby incorporated
by reference in its entirety.
FIELD
[0002] This disclosure relates to the field of quantum dots,
polymers containing quantum dots, methods of making the quantum
dots and polymers containing them as well as methods of using
them.
BACKGROUND
[0003] Much research has been devoted to improving the stability
and useable life of quantum dots and their ease of manufacture and
use. Applicants have developed several techniques and quantum dots
that each contribute to improved stability, ease of manufacture,
and/or ease of use.
[0004] Nie (U.S. Pat. Nos. 7,981,667 and 84,201,550) and Qu (U.S.
Pat. No. 8,454,927), each of which is hereby incorporated by
reference in its entirety, disclose methods of making quantum dots
that are tunable by stoichiometry, rather than by size.
Particularly, alloy-gradient quantum dots disclosed therein are
particularly stable. These quantum dots are more stable than
predecessor dots, benefit from ease of manufacture-since split
second timing is no longer required to obtain the right size and
therefore the desired emission wavelength. These quantum dots
further benefit from uniform size, regardless of emission
wavelength, which allows for uniform handling and processing, which
is not possible with size-tunable quantum dots, which require
different sized quantum dots to achieve a spectrum of colors.
[0005] These stoichiometrically-tuned quantum dots were further
stabilized by capping, in some instances with ZnS, resulting in a
capped alloy-gradient stoichiometrically tuned quantum dot.
[0006] While this advance was, and remains, a significant advance
in quantum dot science, further improvements to stability were
sought. Particularly, quantum dots are sensitive to their
immediate, proximate environment. Applicants found by passivating
the surface of the quantum dot, particularly with atomic layers of
Al.sub.2O.sub.3, stability improved tremendously. The passivation
layer essentially places an optically neutral layer of armor around
the quantum dot, making it incredibly stable. Combining the
advances of the Nie (U.S. Pat. Nos. 7,981,667 and 84,201,550 and Qu
(U.S. Pat. No. 8,454,927) disclosures with the passivation produces
a stable, long-lived, uniformly sized quantum dot. These concepts
are captured in applicants' U.S. Pat. No. 9,425,253, hereby
incorporated by reference.
[0007] Although incredibly stable, well-performing, and long-lived,
these passivated quantum dots are still difficult to handle and
process, and still sensitive to their immediate, proximate
environment and could benefit from a stable electronic environment
immediately proximate their outer surface (e.g. outside the
passivation layer). Accordingly, more, better, and/or different
ways of stabilizing quantum dots, regardless of type, particularly
for optoelectronic applications is desired.
[0008] Further, additional method of making the quantum dots,
themselves, are always sought after.
[0009] Applicants have now discovered that by tightly bonding a
polymer to the outer surface of the quantum dot, stability of the
quantum dot can be maintained even in a variety of harsh
manufacturing conditions, such as, but not limited to, extrusion
molding, injection molding, and other techniques.
[0010] As described further below, in particular embodiments, the
polymer is chosen such that it cross-links with the passivation
layer (e.g. Al.sub.2O.sub.3) of the quantum dot such that the bond
dissociation energy associated with the polymer/passivation layer
is greater than the energy needed to melt the cross-linked polymer.
In other words, the bond between the polymer and the passivation
layer is not broken at extrusion (or other manufacturing)
temperatures. This tight bond essentially protects the quantum dot
during melting operations such as extrusion and injection molding.
Previously, quantum dots exposed to such temperatures simply went
dark, their optoelectronic properties extinguished by the
processing conditions.
[0011] Described herein are methods for making quantum
dot-containing polymer resins and the polymer resins themselves.
These methods are applicable to various types of quantum dots
provided the polymer can tightly bond to the surface of the quantum
dot.
SUMMARY
[0012] Some embodiments provide a method for synthesizing II-VI-VI
semiconductor nanocrystals (SCNs) of the formula
WY.sub.xZ.sub.(1-x) having a predetermined emission wavelength,
wherein W is a Group II element, Y and Z are different Group VI
elements, and 0<X<1, comprising heating a II-VI-VI SCN
precursor solution to a temperature sufficient to produce the
II-VI-VI SCNs, wherein the II-VI-VI SCN precursor solution
comprises a Group II element, a first Group VI element, a second
Group VI element, and a pH controller in one or more solvents
together comprising one or more C.sub.12 to C.sub.20 hydrocarbons
and one or more fatty acids; and
[0013] wherein the amount of pH controller is adjusted to provide
the predetermined emission wavelength from the SCNs.
[0014] In some embodiments, the Group II element is one or more
selected from Cd, Zn and Hg.
[0015] In some embodiments, each of the first Group VI element and
the second Group VI element is one or more selected from S, Se, Te,
Po, and O.
[0016] In some embodiments, the C.sub.12 to C.sub.20 hydrocarbons
are one or more selected from hexadecene, octadecene, eicosene,
hexadecane, octadecane and Icosane.
[0017] In some embodiments, the fatty acids are one or more
selected from myristoleic acid, palmitoleic acid, sapienic acid,
oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic
acid, .alpha.-Linolenic acid, arachidonic acid, eicosapentaenoic
acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic
acid, and arachidic acid.
[0018] In some embodiments, the pH controller is an oxide or
carboxylic acid salt of a Group II element.
[0019] In some embodiments, pH controller is selected from zinc
salts of acetic acid, citric acid, lactic acid, propionic acid,
butyric acid, tartaric acid, and valeric acid.
[0020] In some embodiments, the II-VI-VI SCN precursor solution is
prepared by: dissolving the Group II element, the first Group VI
element, and the second Group VI element in a solvent comprising
the pH controller, octadecene and a fatty acid to provide the
II-VI-VI SCN precursor solution.
[0021] In some embodiments, the II-VI-VI SCN precursor is prepared
by preparing a first solution by dissolving the Group II element
and the first Group VI element in a first solvent comprising
octadecene and a fatty acid; preparing a second solution by
dissolving the second Group VI element in a second solvent
comprising octadecene; mixing the first and second solutions to
provide a II-VI-VI SCN precursor solution; adding the pH controller
to one or both of the first and second.
[0022] In some embodiments, the II-VI-VI SCN precursor solution is
prepared by preparing a first solution by dissolving a Group II
element in a first solvent comprising octadecene and a fatty acid;
preparing a second solution by dissolving a first Group VI and a
second Group VI element in a second solvent comprising octadecene;
adding the pH controller to one or both of the first and second
solutions; and mixing said first and second solutions to provide a
II-VI-VI SCN precursor solution.
[0023] In some embodiments, the II-VI-VI SCN precursor is prepared
by: preparing a first solution by dissolving a Group II element in
a first solvent comprising octadecene and a fatty acid; preparing a
second solution by dissolving a first Group VI element in a second
solvent comprising octadecene; preparing a third solution by
dissolving a second Group VI element in a third solvent comprising
tributylphosphine; adding the pH controller to one or more of the
first, second, or third solutions; and mixing the first, second,
and third solutions to provide a II-VI-VI SCN precursor
solution.
[0024] In some embodiments, the fatty acid is oleic acid.
[0025] In some embodiments, the temperature is between about
270.degree. C. and 330.degree. C.
[0026] Some embodiments provide a II-VI-VI semiconductor
nanocrystals made according to the methods disclosed herein.
[0027] Some embodiments provide a II-VI-VI semiconductor
nanocrystal comprising Cd, S and Se, where in the nanocrystal has
been modified by a zinc alkylcarboxylate pH controller.
[0028] Some embodiments provide a method of tuning a II-VI-VI
semiconductor nanocrystal of known emission wavelength, the method
comprising: providing a II-VI-VI semiconductor nanocrystal having a
known emission wavelength; heating the II-VI-VI semiconductor
nanocrystal in a solution comprising a pH controller, one or more
C.sub.12 to C.sub.20 hydrocarbons and one or more fatty acids to
form an SCN solution; adding a solution comprising dialkyl zinc,
hexaalkyldisilathiane and trialkylphosphine; and heating to a
temperature sufficient to produce a capped II-VI-VI semiconductor
nanocrystal; wherein the amount of pH controller is adjusted to
provide a predetermined emission wavelength shift from the known
emission wavelength of the II-VI-VI semiconductor nanocrystal.
[0029] In some embodiments, the C.sub.12 to C.sub.20 hydrocarbons
are one or more selected from hexadecene, octadecene, eicosene,
hexadecane, octadecane and Icosane.
[0030] In some embodiments, the fatty acids are one or more
selected from myristoleic acid, palmitoleic acid, sapienic acid,
oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic
acid, .alpha.-Linolenic acid, arachidonic acid, eicosapentaenoic
acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic
acid, and arachidic acid.
[0031] In some embodiments, the pH controller is an oxide or
carboxylic acid salt of a Group II element.
[0032] In some embodiments, pH controller is selected from zinc
salts of acetic acid, citric acid, lactic acid, propionic acid,
butyric acid, tartaric acid, and valeric acid.
[0033] In some embodiments, the dialkyl zinc is dimethyl zinc, the
hexaalkyldisilathiane is hexamethyldisilathiane and the
trialkylphosphine is trioctylphosphine.
[0034] In some embodiments, the temperature is between about
150.degree. C. and 350.degree. C.
[0035] Some embodiments provide a tuned II-VI-VI semiconductor
nanocrystal made according to the methods disclosed herein.
[0036] Some embodiments provide a capped II-VI-VI semiconductor
nanocrystal comprising: a core comprising a II-VI-VI semiconductor
nanocrystal comprising Cd, S and Se, wherein the nanocrystal has
been modified by a zinc alkylcarboxylate; and a cap layer selected
from the group consisting of a layer comprising ZnS, a layer
comprising Al.sub.2O.sub.3, and a multi-layer cap comprising a
first layer comprising ZnS and a second layer comprising
Al.sub.2O.sub.3.
[0037] Some embodiments provide a cadmium free "Cd-free"
semiconductor nanocrystal comprising one or more group II elements,
one or more group III elements, and one or more group VI elements,
wherein the semiconductor nanocrystal is substantially free of
cadmium.
[0038] In some embodiments, the semiconductor nanocrystal does not
contain cadmium.
[0039] In some embodiments, the Cd-free nanocrystal have an
emission wavelength in the near ultraviolet to far infrared
range.
[0040] Some embodiments provide a method for synthesizing Cd-free
semiconductor nanocrystals comprising: heating a precursor solution
comprising one or more non-cadmium Group II elements, one or more
Group III elements and one or more Group VI elements in one or more
solvents together comprising one or more C.sub.12 to C.sub.20
hydrocarbons, one or more fatty acids and optionally one or more
C.sub.1 to C.sub.22 alkyl thiols to a temperature sufficient to
produce the Cd-free semiconductor nanocrystals.
[0041] In some embodiments, the Group II elements are one or more
selected from Cu, Zn and Hg.
[0042] In some embodiments, the Group III elements are one or more
selected from In, Ga, Al, and Tl.
[0043] In some embodiments, the Group VI elements are one or more
selected from S, Se, Te, Po, and O.
[0044] In some embodiments, the C.sub.12 to C.sub.20 hydrocarbons
are one or more selected from hexadecene, octadecene, eicosene,
hexadecane, octadecane and Icosane.
[0045] In some embodiments, the fatty acids are one or more
selected from myristoleic acid, palmitoleic acid, sapienic acid,
oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic
acid, .alpha.-Linolenic acid, arachidonic acid, eicosapentaenoic
acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic
acid, and arachidic acid.
[0046] In some embodiments, the fatty acid is oleic acid.
[0047] In some embodiments, the temperature is between about
270.degree. C. and 330.degree. C.
[0048] Some embodiments provide a Cd-free semiconductor
nanocrystals made according to the methods disclosed herein.
[0049] Some embodiments provide a Cd-free semiconductor nanocrystal
that has been modified by a zinc alkylcarboxylate.
[0050] Some embodiments provide a method of capping a Cd-free
semiconductor nanocrystal comprising: providing a Cd-free
semiconductor nanocrystal; heating the Cd-free semiconductor
nanocrystal in a solution comprising one or more C.sub.12 to
C.sub.20 hydrocarbons and one or more fatty acids to form an SCN
solution; adding a solution comprising dialkyl zinc,
hexaalkyldisilathiane and trialkylphosphine; and heating to a
temperature sufficient to produce a capped Cd-free semiconductor
nanocrystal.
[0051] In some embodiments, the C.sub.12 to C.sub.20 hydrocarbons
are one or more selected from hexadecene, octadecene, eicosene,
hexadecane, octadecane and Icosane.
[0052] In some embodiments, the fatty acids are one or more
selected from myristoleic acid, palmitoleic acid, sapienic acid,
oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic
acid, .alpha.-Linolenic acid, arachidonic acid, eicosapentaenoic
acid, erucic acid, docosahexaenoic acid, stearic acid, palmitic
acid, and arachidic acid.
[0053] In some embodiments, the dialkyl zinc is dimethyl zinc, the
hexaalkyldisilathiane is hexamethyldisilathiane and the
trialkylphosphine is trioctylphosphine.
[0054] In some embodiments, the temperature is between about
150.degree. C. and 350.degree. C.
[0055] Some embodiments provide a capped Cd-free semiconductor
nanocrystal comprising: a core comprising a Cd-free semiconductor
nanocrystal comprising a core of one or more group II elements, one
or more group III elements, and one or more group VI elements,
wherein the semiconductor nanocrystal is substantially free of
cadmium, wherein the nanocrystal has been modified by a zinc
alkylcarboxylate; a cap layer selected from the group consisting of
a layer comprising ZnS; and a layer comprising Al.sub.2O.sub.3.
[0056] Some embodiments provide a quantum dot-containing polymer
resin comprising: a plurality of quantum dots, each having an
outermost layer; a polymer material cross-linked to the outermost
layer such that the bond dissociation energy between the polymer
material and the outermost layer is greater than the energy
required to reach the melt temperature of the cross-linked
polymer.
[0057] In some embodiments, the plurality of quantum dots are
selected from core-shell quantum dots, Cd-free quantum dots, or
stoichiometrically tuned quantum dots.
[0058] In some embodiments, the outermost layer is selected from a
capping layer and a passivation layer.
[0059] In some embodiments, the outermost layer is a Zns capping
layer.
[0060] In some embodiments, the outermost layer is an Al2O3
passivation layer.
[0061] In some embodiments, the polymer material is an acrylate
resin comprising: units derived from polymerizing one or monomers
according to the formula:
##STR00001##
[0062] wherein R.sub.1 is hydrogen or methyl and R.sub.2 is
selected from the group consisting of methyl; ethyl; propyl;
isopropyl; butyl; isobutyl; pentyl; cyclopentyl; isopentyl; linear,
branched and cyclic hexyl; linear, branched and cyclic heptyl; and
linear branched and cyclic octyl.
[0063] In some embodiments, the acrylate resin further comprises
units derived from polymerizing one or monomers according to the
formula:
##STR00002##
[0064] wherein each of R.sub.3 and R.sub.4 are independently
selected from the group consisting of methyl; ethyl; propyl;
isopropyl; butyl; isobutyl; pentyl; cyclopentyl; isopentyl; C.sub.6
to C.sub.12 linear, branched, cyclic and aromatic hydrocarbyl, and
polyethylene glycol; and
[0065] wherein R.sub.5 is selected from the group consisting of
hydrogen, methyl; ethyl; propyl; isopropyl; butyl; isobutyl;
pentyl; cyclopentyl; isopentyl; C.sub.6 to C.sub.12 linear,
branched, cyclic and aromatic hydrocarbyl, and polyethylene
glycol.
[0066] Some embodiments provide a quantum dot containing polymer
resin comprising a plurality of quantum dots each having an
Al.sub.2O.sub.3 passivation layer; a polymer material cross-linked
to the Al.sub.2O.sub.3 passivation layer, wherein the bond
dissociation energy between the polymer material and the
Al.sub.2O.sub.2 is greater than the energy required to reach the
melt temperature of the cross-linked polymer.
[0067] Some embodiments provide a quantum dot-containing polymer
resin comprising: a homogenous plurality of multi-color, same-sized
alloy-gradient quantum dots each having a ZnS capping layer and an
Al.sub.2O.sub.3 passivation layer; a polymer material cross-linked
to the Al.sub.2O.sub.3 passivation layer, wherein the bond
dissociation energy between the polymer material and the
Al.sub.2O.sub.3 is greater than the energy required to reach the
melt temperature of the cross-linked polymer.
[0068] Some embodiments provide a quantum dot containing polymer
resin comprising: a plurality of quantum dots each having a ZnS
capping layer and an Al.sub.2O.sub.3 passivation layer; a polymer
material cross-linked to the Al.sub.2O.sub.3 passivation layer,
wherein the bond dissociation energy between the polymer material
and the Al.sub.2O.sub.3 is greater than the energy required to
reach the melt temperature of the cross-linked polymer.
[0069] Some embodiments provide an article comprising at least one
of a film, a multi-layer film, or a 3D object comprising a quantum
dot-containing polymer, wherein polymer is bound to the quantum-dot
such that the bond dissociation energy between the polymer material
and the quantum dot is greater than the energy required to reach
the melt temperature of the cross-linked polymer.
[0070] In some embodiments, the quantum dot-containing polymer is
suitable for traditional polymer handling and manufacturing
techniques, including but limited to solvent casting, injection
molding, extrusion molding, etc.
[0071] Embodiments relate to semiconductor nanocrystals that can be
tuned to predetermined emission wavelengths.
[0072] In particular embodiments, the nanocrystalline particles
have an emission wavelength in the near ultraviolet (UV) to far
infrared (IR) range, and in particular, the visible range. More
particularly, the quantum dots have an emission wavelength that can
be from about 350 to about 750 nm.
[0073] Some embodiments provide quantum dot cores and semiconductor
nanocrystals that have been modified by a zinc alkylcarboxylate
such as zinc acetate.
[0074] Additional embodiments provide a method for synthesizing
semiconductor core/shell nanoparticles that includes synthesizing a
Cd-free semiconductor nanocrystal as described above, and coating
it with a semiconductor shell with higher bandgap to improve the
quantum efficiency and stability compared with the Cd-free
semiconductor nanocrystals by itself.
[0075] Further embodiments provide a method for synthesizing a
Cd-free semiconductor nanocrystal having a semiconductor shell as
described above and a second shell that acts as an insulator.
[0076] Still further embodiments relate to films and 3-D structures
that include and of the semiconductor nanocrystals, core/shell and
core/shell/shell particles described herein dispersed in a acrylate
resin. The films and 3-D structures provide the ability to cast
films and 3-D structures on commercially applicable equipment
resulting in highly stable quantum dot-polymer composite films and
3-D structures. The films and 3-D structures can be used in display
and lighting applications. In particular aspects, a single-coat
down-conversion film (SCDF) that includes a single layer of the
quantum dot-polymer composite film, sandwiched between at least two
transparent films and 3-D structures can be used. The single and
multilayer inventive films and 3-D structures enable a simpler and
more cost effective product that provides at least the performance
of more complicated structures.
BRIEF DESCRIPTION OF DRAWINGS
[0077] FIG. 1 is a schematic showing a type-I bandgap configuration
and type-II bandgap configurations of core/shell QDs.
[0078] FIG. 2 is a schematic showing valence and conduction bands
of am- and .gamma.-Al2O3 films grown by atomic layer
deposition.
[0079] FIG. 3 is graph comparing intensity over time of CdSe/ZnS
vs. CdSe/ZnS/Al2O3 quantum dots demonstrating the stability
imparted by the Al2O3 passivation layer.
[0080] FIG. 4 depicts the surface of Al2O3 is characterized by a
repeating pattern of electropositive and electronegative
regions.
[0081] FIG. 5 is another depiction of the repeating pattern of
electropositive and electronegative regions of the Al2O3
surface.
[0082] FIG. 6 is graph comparing intensity over time of polymer
encapsulated quantum dots in accordance with some embodiments,
showing stability of the polymer encapsulated quantum dots over
time.
[0083] FIG. 7 depicts a multilayer film that includes a film
containing quantum dot cores in accordance with some
embodiments.
[0084] FIG. 8 depicts the effect of varied refractive indexes as
employed by different embodiments disclosed herein.
[0085] FIG. 9 depicts a multilayer film that includes multiple
layers, including a film containing quantum dot cores in accordance
with some embodiments.
[0086] FIG. 10 is a chart showing the emission spectrum for
exemplary Cd-Free quantum dots in accordance with some
embodiments.
[0087] FIG. 11 is a graph comparing stability testing of examples
B13 and B15 disclosed herein.
[0088] FIG. 12 is a calibration curve developed from the data
associated with examples B1 through B6 disclosed herein.
[0089] FIG. 13 is a calibration curve developed from the data
associated with examples B7 through B11 disclosed herein.
[0090] FIG. 14 is an emission spectra of the solvent cast film of
example B22 made using excitation at 450 nm and the emission in the
red wavelengths of the spectra.
[0091] FIG. 15 is an emission spectra of the melt extruded film of
example B23 made using excitation at 450 nm and the emission in the
red wavelengths of the spectra.
DETAILED DESCRIPTION
[0092] Applicants have now discovered that by tightly bonding a
polymer to the outer surface of the quantum dot, stability of the
quantum dot can be maintained even in a variety of harsh
manufacturing conditions, such as, but not limited to, extrusion
molding, injection molding, and other techniques.
[0093] As described further below, in particular embodiments, the
polymer is chosen such that it cross-links with the passivation
layer (e.g. Al.sub.2O.sub.3) of the quantum dot such that the bond
dissociation energy associated with the polymer/passivation layer
is greater than the energy needed to melt the cross-linked polymer.
In other words, the bond between the polymer and the passivation
layer is not broken at extrusion (or other manufacturing)
temperatures. This tight bond essentially protects the quantum dot
during melting operations such as extrusion and injection molding.
Previously, quantum dots exposed to such temperatures simply went
dark, their optoelectronic properties extinguished by the
processing conditions.
[0094] Described herein are methods for making quantum dots,
quantum dot-containing polymer resins and the polymer resins
themselves. These methods are applicable to various types of
quantum dots provided the polymer can tightly bond to the surface
of the quantum dot.
[0095] By tightly bonding a polymer to the outer surface of the
quantum dot, particularly a passivated quantum dot, stability of
the quantum dot can be maintained even in a variety of harsh
manufacturing conditions, such as, but not limited to, extrusion
molding, injection molding, cast molding, solvent casting, and
other techniques.
[0096] As described further below, in particular embodiments, the
polymer is chosen such that it cross-links with the passivation
layer (e.g. Al.sub.2O.sub.3) of the quantum dot such that the bond
dissociation energy associated with the bonds between the polymer
and the passivation layer is greater than the energy needed to melt
the cross-linked polymer. In other words, the bond between the
polymer and the passivation layer is not broken at melt
temperatures incurred, for example during extrusion (or other
manufacturing) processes. This tight bond essentially protects the
quantum dot during melting operations such as extrusion and
injection molding. Previously, quantum dots exposed to such
temperatures simply went dark, their optoclectronic properties were
extinguished by the processing conditions.
[0097] Described herein are methods for making quantum
dot-containing polymer resins and the polymer resins themselves.
These methods are applicable to various types of quantum dots
provided the polymer can tightly bond to the surface of the quantum
dot.
[0098] As noted above, although improved stability can be had by
using the polymers and methods disclosed herein with any quantum
dot, be it homogenous or alloy-gradient, size-tuned or
stoichiometrically tuned, capped or uncapped, passivated or
unpassivated, so long as the polymer can tightly bind to the outer
surface of the quantum dot, achieving efficient and stable quantum
dot (QD) photoluminescense, over the visible range of light, under
the combined conditions of high photon flux and chemically adverse
external environments benefits from a multi-tiered approach.
[0099] First, the QD cores should have a similar surface area
across the visible range. Additionally, it is specifically
contemplated that cadmium-free (Cd-free) quantum dots may also be
used in the methods and polymers described herein. Any Cd-free
quantum dot may be used, but those described in U.S. Provisional
Patent Application No. 62/338,915 entitled Cadmium-Free Quantum
Dots, the disclosure of which is incorporated by reference, and set
forth below, are well-suited for use with the methods and polymers
disclosed herein.
[0100] Second, core passivation should provide both confinement of
the exciton wavefunction to the core and a physical barrier to
water and oxygen.
[0101] Third, the dispersive matrix that provides separation in
space for the individual QDs must also provide a stable electronic
configuration outside the QD volume that is conducive to
photoluminescense, while itself being stable against
photodegradation. The embodiment of these three elements into
usable materials for the thermoplastic, thermoset and solvent cast
production of optical components would accelerate the acceptance of
quantum dot based components for display and lighting
applications.
[0102] 1. The Core
[0103] It is a basic property of metal and semiconductor materials
that their propensity for chemical reactions increases with an
increase in surface area to mass. Thus, a 1 cm cube of metal will
simply heat up when exposed to flame while that same mass will
ignite if ground to a micron-sized powder. The same is true of QD
cores with respect to environmental degradation and
photodegradation. QDs tuned by core size will differentially
degrade due to the increased reactivity of smaller cores
(blue-green emitters) versus larger cores (yellow-red emitters)
because of a higher surface area to mass ratio. This is true in
both situations of environmental attack by water and oxygen and
under conditions of high photon flux where destructive free
radicals are created on the QD surface. At the surface of QDs,
there is a population of atoms that are incompletely part of the
periodic 3D crystal lattice of the interior. These atoms have
vacant or lone-pair electron orbitals. These dangling bonds are the
source of undesired chemical reactions both with the external
environment and in non-radiative carrier relaxation processes
during the photoluminescent emission cycle in which electrons pool
at these sites instead of recombining with a hole. This effect is
magnified with smaller QDs that have a higher surface area/mass
ratio than larger QDs.
[0104] Thus, in an optical device composed of multi-colored
size-tuned QDs, it is likely that faster degradation of the QDs
emitting at the blue end of the visible spectrum will be observed
over time, especially under conditions of exposure to water and
oxygen combined with high photon flux. It is desirable to have all
QD cores in an optoelectronic device be of similar size.
[0105] This desired core configurations can be achieved by using
QDs synthesized by the methods of Nie (U.S. Pat. Nos. 7,981,667 and
84,201,550 and Qu (U.S. Pat. No. 8,454,927). These QDs are tuned by
composition and not by size.
[0106] While same color size-tunable dots could be used, when
considering the entire visible range, stoichiometrically-tuned
quantum dots advantageously have the same size regardless of
emission wavelength. Stoichiometrically-tuned quantum dots can be
made in accordance with the Nie and Qu patents discussed above or
other available methods. An improved method, involving the use of a
pH controller to fine tune the emission wavelength is disclosed in
U.S. Provisional Patent Application No. 62/338,888 entitled Tunable
Semiconductor Nanocrystals And Films And 3-D Structures Containing
Them the disclosure of which is incorporated by reference and set
forth below herein. Quantum dots made by the methods disclosed
therein result in core/shell quantum dots having substantially the
same size regardless of emission wavelength.
[0107] Capping (i.e. First Passivation Layer)
[0108] There are two methods to passivate the dangling bonds on the
surface of QDs for higher quantum efficiency (QE) and improved
photo/chemical stability: 1) passivating with low MW organic
ligands or 2) passivating with inorganic shells. Passivation with
organic ligands is simple and straightforward but the surface
metal-organic ligand bond is relatively unstable and can be broken
and displaced by chemical and/or photochemical reactions.
Passivation with inorganic shells is embodied by the well-known
core-shell type of QD, and is often referred to as "capping" such
as with a ZnS shell. The surface passivation of QD cores with
inorganic shells is more stable and has the additional desired
effect of providing better confinement of the exciton wavefunction
to the core, thus increasing QE. If a QD core is located within a
shell material with a larger bandgap energy, the electron and hole
wavefunctions are better confined to the core. The recombination
probability of the two wavefunctions (electron and hole) increases
while the non-radiative decay process via interaction with dangling
bonds on the surface decreases. Bandgap and electronic energy
levels for common group II-VI, III-V and II-VI semiconductors are
shown in FIG. 1.
[0109] These core-shell structures are improved with respect to QE
and photostability (PS) but are still susceptible to chemical
attack by water and oxygen from the environment.
[0110] This capping is present in traditional core-shell quantum
dots, and can be applied to a number of quantum dots, including the
Cd-Free quantum dots and the stoichiometrically/pH controller tuned
quantum dots disclosed herein, as well as other quantum dots.
[0111] 2. Passivation (Second Layer):
[0112] It is desirable to provide a second shell of an even wider
bandgap material over the first shell that would further confine
the exciton wavefunction, passivate the dangling bonds on the outer
surface of the first shell material and provide a physical barrier
to the diffusion of water and oxygen.
[0113] This can be realized by adding a second shell, a passivation
layer, of Al2O3 as described in U.S. Pat. No. 9,425,253 (Qu and
Miller) hereby incorporated by reference. The bandgap of Al2O3 is
between -3.5 and -11 (FIG. 2) which encompasses the commonly used
II-VI and III-V QD core and shell materials.
[0114] In addition to having a bandgap energy that encompasses the
commonly used QD core-shell materials, Al2O3, at a thickness of 4-5
atomic layers, has the additional property of providing an absolute
or near-absolute barrier to the diffusion of oxygen and water. This
provides a high barrier of protection from chemical attack by water
and oxygen on the sensitive core-shell semiconductor materials.
[0115] FIG. 3 shows the improved stability achieved by coating a
traditional CdSe/ZnS core-shell quantum dot with an Al2O3
passivation layer.
[0116] 3. The Dispersive Matrix (i.e. the Polymer)
[0117] The Al2O3 surface layer offers unique synergistic
opportunities to provide a matrix for QD dispersion that is
chemically stable and electronically stable at the QD/matrix
interface. The surface of Al2O3 is characterized by a repeating
pattern of electropositive and electronegative regions as seen in
FIGS. 4 and 5.
[0118] QDs with an Al2O3 surface show very tight binding affinities
to organic ligands containing --COOH and --SH groups and also
polymers with repeating carbonyl groups, such as polymers described
in invention disclosures by Nulwala assigned to Crystalplex (U.S.
Patent Application Ser. Nos. 62/338,888 and 62/338,915 both filed
on May 19, 2016 and incorporated herein by reference) and Ser. No.
14/725,658, which is hereby incorporated by reference. This tight
bonding has multiple desirable effects in the resulting
QD/ligand/polymer matrix.
[0119] 3.1 Stability of the Electronic Configuration Immediately
Outside of the QD Volume
[0120] It is known that the electronic configuration of the volume
immediately adjacent to the QD surface and extending out to the
Exciton Bohr Radius can affect the overall QE of a QD population.
(see, X. Ji. D. Copenhaver, C. Sichmeller, and X. Peng, "Ligand
bonding and dynamics on colloidal nanocrystals at room temperature:
the case of alkylamines on CdSe nanocrystals," J. Am. Chem. Soc.
130(17), 5726-5735 (2008). S. F. Wuister. C. de Mello Donega, and
A. Meijerink, "Influence of Thiol Capping on the Exciton
Luminescence and Decay Kinetics of CdTe and CdSe Quantum Dots," J.
Phys. Chem. B 108(45), 17393-17397 (2004).) This is commonly seen
when exchanging small MW organic ligands on the surface of a QD.
Even though the QD nanocrystal is not physically changed by the
process, a change in photoluminescent QE is observed. What is
desired is a local electronic configuration that results in high QE
for the QD and a very stable interface between the QD surface and
the external matrix that remains unchanged even under extremes of
temperature, high photon flux and destructive chemical
environments. This can be achieved by binding the Al2O3 surface of
the QD to polymers such as those disclosed by Nulwala. The overall
binding energy of the matrix polymer to the Al2O3 surface can
exceed the energy of a 280.degree. C. extrusion process and provide
a stable QD/matrix interface.
[0121] 3.2 Chemical Stability of the QD/Matrix Interface
[0122] In addition to heat, the stability of the QD/matrix
interface also can be compromised by the presence of oxygen free
radicals. These destructive free radicals can be produced at the
QD/matrix interface by a combination of high photon flux and the
presence of O2 molecules. The destructive radicals can result in
the breaking of covalent bonds in the polymer chains in the matrix
(chain scission) and/or disruption of the multiple ionic bonds
between the matrix polymer chains and the Al2O3 surface of the
QDs.
[0123] The QD/matrix interface can be made resistant to oxygen free
radical attack by a combination of the redundancy of ionic bonds
between matrix polymers and the Al2O3 surface and the intrinsic
high O2 barrier properties of the matrix polymer. Specific
polymers, notably homopolymers of cyclohexyl acrylate and
cyclohexyl acrylate copolymers with methyl methacrylate or heptyl
acrylate have repeating carbonyl units oriented in 3D space such
that the electronegative carbonyl oxygen repeat distance matches
with the repeat distance of the electropositive regions on the
surface of Al2O3. This leads to very tight bonding of the polymer
to the Al2O3 surface due to a multitude of binding sites per
polymer chain.
[0124] In addition, these acrylic polymers have high O2 barrier
properties. The combined effect of suspending QDs in these matrices
is very stable bonding of the polymers to the QD surface and
minimal O2 diffusion to the binding site.
[0125] 3.3 Stable Dispersion in the 3D Matrix Volume
[0126] In addition to the chemical stability of the QD/matrix
interface, the QDs must be well dispersed without clumping to
function properly in photoluminescent mode.
[0127] The polymers described in 3.2, and others disclosed by
Nulwala, disperse QDs in this fashion. This is due to the fact that
the polymer-QD bonding is more stable than QD-QD self bonding. Once
bound in this fashion the QD/matrix is stable throughout downstream
processing such as thermoplastic, thermoset and solvent-casting
operations. In addition, the physical properties of the polymer
matrix can be improved by the interaction with the QD
nanoparticles. The physical crosslinking sites provided by the QDs
can change and improve the physical properties of the polymer such
as glass transition temperature, durometer, impact resistance,
tensile strength and chemical resistance.
[0128] 4. Processing
[0129] 4.1 Preparation of the Composite
[0130] The QD/polymer composite can be prepared by multiple
methods.
[0131] Polymers can be polymerized in a continuous reactor and QDs
can be introduced into the continuous stream either before or after
complete polymerization. The resulting QD/polymer composite stream
can then be collected and the solvent removed for use as a
thermoplastic material to produce an optical component. Solvent may
be retained or added to produce a solvent casting composite to
produce an optical film.
[0132] Polymers can be completely polymerized then mixed with QDs
in an appropriate solvent. Mixing, such as high shear mixing, can
be applied to increase binding of polymers to the QD surface. The
QD/polymer composite can be left as is for use in solvent film
casting or the solvent can be removed to produce a dry composite
for thermoplastic processing to produce optical components.
[0133] QDs can be suspended in monomer or a mixture of monomers or
a mixture of monomers and oligomers or a mixture of monomers and
multifunctional monomers with multiple vinyl groups that produce
crosslinking in the final polymer. This thermoset material can
later be cured by heat or UV radiation to produce the final optical
component.
[0134] 4.1 Downstream Processing of the Composite
[0135] The three commonly used processes to produce optical
components from plastics are thermoplastic, thermoset, and solvent
casting.
[0136] Included in these general categories are injection molding,
extrusion, thermoset potting, thermoset film, solvent cast film,
solvent cast ink jet printing, solvent cast 3D printing, thermoset
ink jet printing, thermoset 3D printing, thermoplastic 3D printing,
and other techniques.
[0137] Other than in the operating examples or where otherwise
indicated, all numbers or expressions referring to quantities of
ingredients, reaction conditions, etc. used in the specification
and claims are to be understood as modified in all instances by the
term "about." Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the following specification and
attached claims are approximations that can vary depending upon the
desired properties, which the present invention desires to obtain.
At the very least, and not as an attempt to limit the application
of the doctrine of equivalents to the scope of the claims, each
numerical parameter should at least be construed in light of the
number of reported significant digits and by applying ordinary
rounding techniques.
[0138] Notwithstanding that the numerical ranges and parameters
setting forth the broad scope of the invention are approximations,
the numerical values set forth in the specific examples are
reported as precisely as possible. Any numerical values, however,
inherently contain certain errors necessarily resulting from the
standard deviation found in their respective testing
measurements.
[0139] Also, it should be understood that any numerical range
recited herein is intended to include all sub-ranges subsumed
therein. For example, a range of "1 to 10" is intended to include
all sub-ranges between and including the recited minimum value of 1
and the recited maximum value of 10; that is, having a minimum
value equal to or greater than 1 and a maximum value of equal to or
less than 10. Because the disclosed numerical ranges are
continuous, they include every value between the minimum and
maximum values. Unless expressly indicated otherwise, the various
numerical ranges specified in this application are
approximations.
[0140] As used herein, the singular forms "a", "an" and "the"
include plural reference unless the context clearly dictates
otherwise.
[0141] As used herein, the term "about" means plus or minus 10% of
the numerical value of the number with which it is being used.
Therefore, about 50% means in the range of 45%-55%.
[0142] As used herein, the term "copolymer" means a polymer
resulting from the polymerization of two or more polymerizable
unsaturated molecules and is meant to include terpolymers, tetra
polymers, etc.
[0143] As used herein, the term "core/shell" means particles that
have a quantum dot as a core and one or more shells or coatings
generally uniformly surrounding the quantum dot core. Non-limiting
examples of shell materials include Cd or Zn salts of S or Se
and/or metal oxides.
[0144] The terms "include," "comprise," and "have" and their
conjugates, as used herein, mean "include but not necessarily
limited to."
[0145] As used herein, the term "Group II element" is meant to
include one or more elements from the IUPAC group 2 of the periodic
table selected from Cd, Zn and Hg, except when discussing Cd-free
embodiments, in which case Group II element refers one or more
elements from the IUPAC group 2 of the periodic table selected from
Cu, Zn and Hg.
[0146] As used herein, the term "Group VI element" is meant to
include one or more elements from the IUPAC group 16 of the
periodic table selected from S, Se, Te, Po, and O.
[0147] As used herein, the terms "nanoparticles", "nanocrystals",
and "passivated nanocrystals" refer to small structures in which
the ordinary properties of their constituent materials are altered
by their physical dimensions due to quantum-mechanical effects,
often referred to as "quantum confinement." For the sake of
clarity, the use of these terms in this disclosure refers to
objects possessing quantum-confinement properties, which are
separated from one another in all three dimensions; enabling
incorporation into liquids, vapors, or solids.
[0148] "Optional" or "optionally" means that the subsequently
described structure, event, or circumstance may or may not be
present or occur, and that the description includes instances where
the structure is present and where it is not or instances where the
event occurs and instances where it does not.
[0149] As used herein, the term "polymer" is meant to encompass,
without limitation, oligomers, homopolymers, copolymers and graft
copolymers.
[0150] As used herein, the term "quantum dot" typically refers to a
nanocrystalline particle made from a material that in the bulk is a
semiconductor or insulating material, which has a tunable
photophysical property in the near ultraviolet (UV) to far infrared
(IR) range, and in particular, the visible range. In many
embodiments of the present invention the term quantum dot includes
semiconductor nanocrystals (SCN) that include transition metals,
non-limiting examples being Cd and Zn, and anions from the IUPAC
group 16 of the periodic table, non-limiting examples being Se, S,
Te, and O.
[0151] As used herein, the term "composite" refers to materials
that contain quantum dots and a polymer combined into a matrix that
includes quantum dots dispersed throughout the matrix. In some
embodiments, the quantum dots are dispersed substantially evenly
throughout the matrix.
[0152] Aspects of this disclosure relate to semiconductor
nanocrystals tuned to a predetermined emission wavelength (i.e. a
quantum dot). In some instances, the quantum dots may be a
plurality of quantum dots containing a ranges of predetermined
emission wavelengths. Particularly, in some embodiments, a
plurality of quantum dots contains a homogenous mixture of quantum
dots emitting a desired plurality of desired wavelengths.
[0153] Aspects of the present invention relate to films and 3-D
structures comprising core/shell quantum dot particles dispersed in
a acrylate resin. The films and 3-D structures provide the ability
to cast films and place 3-D structures onto commercially applicable
equipment resulting in highly stable quantum dot-polymer composite
films and 3-D structures. The inventive films and 3-D structures
can be used in display and lighting applications. In particular
aspects, a single-coat down-conversion film (SCDF) that includes a
single layer of the quantum dot-polymer composite film, sandwiched
between at least two transparent films and 3-D structures can be
used. The single and multilayer inventive films and 3-D structures
enable a simpler and more cost effective product that provides at
least the performance of more complicated structures.
The Quantum Dot Core
[0154] Any semiconductor nanocrystals known in the art may be used
as the core for the quantum dots for incorporation into the
polymers described herein, non-limiting examples being the relevant
semiconductor nanocrystals disclosed in U.S. Pat. Nos. 6,207,229;
6,322,901; 6,576,291; 6,821,337; 7,138.098; 7,825,405; 7,981,667;
8,071,359; 8,288,152; 8,288,153; 8,420.155; 8,454.927; 8,481,112;
8,481,113; 8,648,524; 9,063,363; and 9,182,621 and U.S. Published
Patent Application Nos. 2006/0036084, 2010/0270504, 2010/0283034;
2012/0039859; 2012/0241683; 2013/0335677; 2014/0131632; and
2014/0339497.
[0155] The quantum dots employed herein may be any quantum dot, and
may be:
[0156] a) cadmium-containing or cadmium free
[0157] b) alloy-gradient or non-gradient (i.e. homogenous)
[0158] c) size-tunable, stoichiometrically-tunable, or not, or
[0159] d) any combination of these.
[0160] Additionally, contemplated herein are new methods of making
quantum dots, particularly a method of making same-size
stoichimetrically and pH controller-tuned quantum dots and Cd-free
quantum dots are disclosed herein, in and of themselves, and also
for incorporation into the polymers as disclosed herein.
[0161] Thus, traditional core/shell quantum dots such as those that
are commercially available, other Cd-free quantum dots, as well as
the same-size stoichimetrically and pH controller-tuned quantum
dots and Cd-free quantum dots described and disclosed herein may be
incorporated into the polymers as described further below.
[0162] Cd-Free Quantum Dots
[0163] As used herein, the term "Cd-free" means the object so
described is substantially free of cadmium or was made without
using cadmium, or does not contain cadmium. For example, the terms
"Cd-free semiconductor nanocrystals" and Cd-free semiconductor
quantum dots" refer to semiconductor nanocrystals or quantum dots
that are substantially free of, made without using or do not
contain cadmium.
[0164] "Substantially free of cadmium" means containing less than
5% cadmium, less than 3% cadmium, less than 1%, less than 0.5%,
less than 0.3%, less than 0.1% or any range of values between any
two of these values and any value there between.
[0165] As used herein, with respect to Cd-Free quantum dots, the
term "Group II element" is meant to include one or more elements
from the IUPAC group 2 of the periodic table selected from Cu, Zn
and Hg.
[0166] As used herein, the term "Group III element" is meant to
include one or more elements selected from In, Ga, Al, and Tl.
[0167] As used herein, the term "Group VI element" is meant to
include one or more elements from the IUPAC group 16 of the
periodic table selected from S. Se, Te, Po, and O.
[0168] In some embodiments, suitable Cd-free semiconductor
nanocrystals that can provide useful quantum dot cores include, but
are not limited to, II-II-III-VI semiconductor nanocrystals (SCN)
of the formula ABCD where A is a Group II element, B is another
group II element, C is a group III element, and D is a group VI
element.
[0169] In particular embodiments the Group II element can be one or
more selected from Cu, Zn and Hg, the group III element can be one
or more selected from In, Ga, Al, and the group VI element can be
can be one or more selected from S. Se, Te, Po, and O.
[0170] In particular embodiments, the Cd-free nanoparticles are
ZnCuInS and/or ZnCuGaS
[0171] In other particular embodiments, suitable semiconductor
nanocrystals that can provide useful Cd-free quantum dot cores in
the invention include II-II-III-III-VI semiconductor nanocrystals
(SCN) of the formula ABCDE where A is a first Group II element, B
is second group II element, C is a first group III element, D is a
second III group element, and E is a group VI element.
[0172] In further aspects of this particular embodiment the Group
II element can be one or more selected from Cu, Zn and Hg, the
group III element can be selected from In, Ga, Al, and the group Vi
element can be selected from S, Se, Te, Po, and O.
[0173] In additional specific aspects of this particular
embodiment, the Cd-free nanoparticles are ZnCuInAlS and/or
ZnCuInGaS.
[0174] In further embodiments, suitable Cd-free semiconductor
nanocrystals that can provide quantum dot cores useful in the
invention include II-II-III-VI-VI semiconductor nanocrystals (SCN)
of the formula ABCDE where A is a first Group II element, B is
second group II element, C is a group III element, D is a first
group VI element, and E is a second group element.
[0175] In aspects of this further embodiment the Group II element
can be one or more selected from Cu, Zn and Hg, the group III
element In, Ga, Al, and the group Vi element can be selected from
S, Se, Te, Po, and O.
[0176] In a specific aspect of this further embodiment, the Cd-free
nanoparticles are ZnCuInSSe, ZnCuGaSSe, ZnCuAlSSe and combinations
thereof.
[0177] In additional embodiments, suitable Cd-free semiconductor
nanocrystals that can provide quantum dot cores useful in the
invention include II-II-III-III-VI-VI semiconductor nanocrystals
(SCN) of the formula ABCDEF, where A is a first Group II element, B
is a second group II element, C is a first group III element, D is
a second group III element, and D is a group element. E is a first
group VI element, and F is a second group VI element.
[0178] In aspects of this additional embodiment the Group II
elements can be one or more selected from Cu, Zn and Hg, the group
III elements can be one or more selected from In, Ga, Al, and the
group Vi elements can be one or more selected from S, Se, Te, Po,
and O.
[0179] In specific aspects of this additional embodiment, the
Cd-free nanoparticles can be ZnCulnAlSSe, ZnCuInGaSSe, ZnCuAlGaSSe
and combinations thereof.
[0180] Source of Group II and Group III Elements
[0181] In some embodiments, the source of the group II and group
III elements are metal oxides.
[0182] In particular embodiments, source of the group II and group
III elements can be selected from ZnO, CuO, In2O3, Al2O3.
[0183] In some embodiments, the source of the group II and III
elements are fatty acid salts.
[0184] In particular embodiments, the group II and group III
elements can be selected from ZnX, CuX, InX, AlX, X can be a
carboxylic acid with chain length from C1 to C22.
[0185] Any suitable carboxylic acid can be used. In some
embodiments, the carboxylic acids used can be one or more selected
from acetic acid, propionic acid, butyric acid, myristoleic acid,
palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic
acid, linoleic acid, linoelaidic acid, .alpha.-Linolenic acid,
arachidonic acid, eicosapentaenoic acid, erucic acid,
docosahexaenoic acid, stearic acid, palmitic acid, and arachidic
acid.
[0186] In a particular embodiment, the carboxylic acid is oleic
acid.
[0187] In a specific embodiment, the carboxylic acid is acetic
acid.
[0188] Source of VI Elements
[0189] In some embodiments, the source of the group VI elements is
a pure elemental powder.
[0190] In particular embodiments, the group VI elements can be
selected from elemental S, Se, Te, Po, and O.
[0191] In some embodiments, the source of the group VI elements are
group VI element containing molecules.
[0192] In particular embodiments, the group VI element is present
as the corresponding thiolate of a single functional alkyl thiol
containing molecule, such as but not limited to, alkyl thiols with
a chain length of from C1 to C22.
[0193] In specific embodiments, the group VI element is the
thiolate of 1-Dodecanthiol.
[0194] In particular embodiments, the group VI element can be a
dithiolate of the corresponding dithiol molecules, such as but not
limited to those dithiol molecules having a chain length of from C1
to C22.
[0195] Ligands
[0196] In embodiments, the Cd-free nanoparticles are coated with
ligands.
[0197] In particular embodiments, the ligands can be selected from
single chain fatty acids with chain lengths from C8 to C22.
[0198] Any suitable fatty acid can be used. In some embodiments,
the fatty acids used can be one or more selected from myristoleic
acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid,
vaccenic acid, linoleic acid, linoelaidic acid, .alpha.-Linolenic
acid, arachidonic acid, eicosapentaenoic acid, erucic acid,
docosahexaenoic acid, stearic acid, palmitic acid, caprylic acid
and arachidic acid.
[0199] In specific embodiments, the fatty acid ligands include
caprylic or octanoic acid.
[0200] In particular embodiments, the ligands can be selected from
single chain thiols with chain lengths from C1 to C22.
[0201] In specific embodiments, the ligands include
1-Dodecanthiol.
[0202] In particular embodiments, the ligands can be a mixture of
fatty acid and long chain thiols with a chain length of from C1 to
C22.
[0203] In specific embodiments, the ligands are a mixture of
1-Dodecanthiol and Octanoic acid.
[0204] Solvent
[0205] In some embodiments, the solvents used for the synthesis of
Cd-free nanoparticles include one or more C12 to C20 hydrocarbons.
In many embodiments, the precursor solution solvents can be chosen
as required by the physical properties of the materials used in the
precursor solution and as required by the apparatus available for
synthesis. In particular embodiments, a high boiling organic
solvent is employed, typically with a boiling point above about
150, in some cases above about 200, and in other cases above about
225.degree. C.
[0206] In particular embodiments, the solvent includes one or more
selected from octadecane, dodecane, hexadecane and icosane.
[0207] In some embodiments, tributylphosphine (TBP) is used as a
solvent in the precursor solution. In other embodiments, a mixture
of TBP and C12 to C20 hydrocarbons are used in the precursor
solution. In these embodiments, including TBP can be advantageous
because it provides a strong dipole moment, which can aid in
dissolving the Group VI elements. In many embodiments, the
precursor solution solvents can be chosen as required by the
physical properties of the materials used in the precursor solution
and as required by the apparatus available for synthesis.
[0208] Cd-Free Core Syntheses
[0209] Some embodiments provide a method for synthesizing Cd-free
semiconductor nanocrystal cores. The method includes heating a
precursor solution that includes the desired mixture of Group II
element(s). Group III elements(s) and Group VI element(s) as
described above in one or more solvents that include one or more
C12 to C20 hydrocarbons and one or more fatty acids to a
temperature sufficient to produce the Cd-free semiconductor
nanocrystal cores.
[0210] In some embodiments, the emission wavelength of the
synthesized Cd-free nanoparticles is determined by molar ratio of
the precursors, and the concentration in and type of C12 to C20
hydrocarbon solvent. Once the proper amounts of chemicals needed
for the syntheses are weighed, they are placed in a suitable
reaction vessel. Without degassing the temperature is raised
sufficiently to initiate the reaction, and keep at that temperature
for a period of time sufficient to allow the reaction to
equilibrate.
[0211] In some embodiments, the reaction temperature is at least
about 200.degree. C., in some cases at least about 220.degree. C.,
in other cases at least about 240.degree. C. and in some instances
at least about 250.degree. C. and can be up to about 300.degree.
C., in some cases up to about 280.degree. C. and in other cases up
to about 270.degree. C. The temperature employed will depend on the
particular precursors and solvents used. The reaction temperature
can be any value or range between any of the values recited
above.
[0212] In some embodiments, the reaction time is at least about 5
minutes, in some cases at least about 8 minutes and in other cases
at least about 9 minutes and can be up to about 60 minutes, in some
cases up to about 45 minutes, in other cases up to about 30 minutes
and in some instances up to about 15 minutes. The reaction time
employed will depend on the particular precursors and solvents
used. The reaction time can be any value or range between any of
the values recited above.
[0213] In a specific embodiment, the reaction time is about 10
minutes.
[0214] Core Purification
[0215] Purification of the Cd-free nanoparticle cores is performed
to substantially reduce or eliminate unreacted precursors and
byproducts generated during the reaction. In some embodiments,
purification of the Cd-free nanoparticle cores can be accomplished
by:
[0216] 1) Transferring the Cd-free nanoparticle core synthesis
solution to a centrifuge tube and diluting to 7.5 times its volume
with a 1:3 mixture of a nopolar and polar solvent (a non-limiting
example being hexanes and butanol).
[0217] 2) Centrifuging the solution from (1) until crystal pellets
form, and pouring off the supernatant.
[0218] 3) Washing the crystals three times with a 1:3 mixture of a
nonpolar and polar solvent (a non-limiting example being hexane and
methanol), using 6.5 times the volume of the original Cd-free
nanoparticle core synthesis solution for each wash. First adding
the nonpolar solvent to suspend the crystals and then adding the
polar solvent to precipitate them.
[0219] 4) Suspending the crystals in a nonpolar solvent (a
non-limiting example being hexane) at 81% the volume of the
synthesis solution.
[0220] Non-Traditional QDs: Stoichiometrically/pH Controlled
Tuning
[0221] The embodiments below relate to a quantum dot made in
accordance with the teachings of U.S. Provisional Patent
Application No. 62/338,888, employing a pH controller in methods
for stoichiometrically tuning QDs to aid in establishing the
desired emission wavelength.
[0222] In some embodiments, the core is a II-VI-VI semiconductor
nanocrystal (SCN) having a predetermined emission wavelength. In
some embodiments, these are made by heating a II-VI-VI SCN
precursor solution that includes a Group II element, a first Group
VI element, a second Group VI element, and a pH controller in one
or more solvents that together include one or more C.sub.12 to
C.sub.20 hydrocarbons and one or more fatty acids to a temperature
sufficient to produce the II-VI-VI SCNs. The amount of pH
controller is adjusted to provide the predetermined emission
wavelength from the SCNs.
[0223] Without wishing to be bound by theory, Applicants believe
that the use of oleic acid creates superior quantum dots because
they are well-suited for subsequent capping, particularly with
ZnS.
[0224] Pre-Cursor Solution
[0225] In some embodiments, suitable semiconductor nanocrystals
that can provide quantum dot cores useful in the present invention
include II-VI-VI semiconductor nanocrystals (SCN) of the formula
WY.sub.xZ.sub.(1-x) where W is a Group II element, Y and Z are
different Group VI elements, and 0<X<1.
[0226] In particular embodiments the Group II element can be one or
more selected from Cd, Zn and Hg and the Group VI element can be
one or more selected from S, Se, Te, Po, and O.
[0227] In some embodiments, the source of the group VI elements is
soluble in C12 to C20 hydrocarbons and are organic miscible with
the one or more fatty acids used to make the II-VI-VI II-VI-VI SCN.
In many embodiments, pure group VI elements in powder form are
used.
[0228] In particular embodiments, a desired predetermined emission
wavelength to be emitted from the SCNs is identified and the amount
of pH controller is adjusted such that the resultant SCNs have the
predetermined emission wavelength.
[0229] pH Controller
[0230] In some embodiments, the amount of pH controller is selected
to tune the emission maximum wavelength of the SCN to the desired
predetermined emission wavelength. When a specific wavelength is
desired, a few synthesis reactions using different concentrations
of pH controllers and, optionally, different molar ratios of
precursors are run to construct a calibration curve. The required
concentration of pH adjuster and, if determined, the required ratio
of precursors are then identified for the desired wavelength from
the calibration curve.
[0231] In particular aspects of this embodiment, the emission
wavelength from the SCNs, without pH controller, can be any
wavelength in the visible range, and in particular from about 400
nm to about 700 nm, and any wavelength between those values. That
is, SCNs can be made with a known emission wavelength. Then by
introduction of a pH controller that emission wavelength can be
"tuned" from that known emission wavelength to a desired
predetermined wavelength.
[0232] When the pH controller is included in the precursor
solution, the emission wavelength of the SCN shifts to a longer
wavelength. In some aspects, the SCN emission wavelength can
increase at least 3 nm, in some cases at least 5 nm and in other
cases at least 7 nm and can increase up to 25 nm, in some cases up
to 20 nm, and in other cases up to 17 nm for each 0.1 weight
percent of pH controller included in the precursor solution. The
amount of SCN emission wavelength can be any value or range between
any of the values recited above. The amount of SCN emission
wavelength increase can vary based on the size of the semiconductor
nanocrystals, the particular pH controller used and the particular
Group II and Group VI elements used. Through manipulation of these
factors, the emission wavelength can be precisely tuned to a
desired emission wavelength.
[0233] The pH controller is included in the precursor solution at a
level that provides the desired SCN emission wavelength increase,
often referred to as "tuning" the SCN. The pH controller can be
present in the precursor solution at a level of from about 0.01
weight percent of the precursor solution, in some cases about 0.1
weight percent of the precursor solution, in other cases about 0.15
weight percent of the precursor solution and in some instances
about 0.2 weight percent of the precursor solution and can be up to
about 1 weight percent of the precursor solution, in some cases up
to about 0.9 weight percent of the precursor solution, in other
cases up to about 0.8 weight percent of the precursor solution and
in some instances up to about 0.7 weight percent of the precursor
solution. The amount of pH controller will be an amount sufficient
to achieve the desired tuning and will typically not exceed an
amount that will increase the SCN emission wavelength beyond the
visible spectrum. The amount of pH controller in the precursor
solution can be any value or range between any of the values
recited above.
[0234] Any pH controller that can maintain a desired pH and effect
the emission wavelength tuning described above can be used in the
SCN solution. In some embodiments, the pH controller can be an
oxide or carboxylic acid salt of a Group II element. In particular
embodiments the pH controller can be selected from zinc salts of
acetic acid, citric acid, lactic acid, propionic acid, butyric
acid, tartaric acid, and valeric acid. In particular embodiments,
the pH controller is an oxide or carboxylic acid salt of a Group II
element.
[0235] In some aspects of the invention, the pH controller is
selected from zinc salts of acetic acid, citric acid, lactic acid,
propionic acid, butyric acid, tartaric acid, and valeric acid.
[0236] In some embodiments, the C12 to C20 hydrocarbons used in the
SCN solution can be one or more selected from hexadecene,
octadecene, eicosene, hexadecane, octadecane and Icosane.
[0237] In other embodiments, the fatty acids used in the SCN
solution can be one or more selected from myristoleic acid,
palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic
acid, linoleic acid, linoelaidic acid, .alpha.-Linolenic acid,
arachidonic acid, eicosapentaenoic acid, erucic acid,
docosahexaenoic acid, stearic acid, palmitic acid, and arachidic
acid.
[0238] Any pH controller that can maintain a desired pH and effect
the emission wavelength tuning described above can be used in the
precursor solution. In some embodiments, the pH controller can be
an oxide or carboxylic acid salt of a Group II element. In
particular embodiments the pH controller can be a salt of an acid
selected from the group consisting of acetic acid, citric acid,
lactic acid, propionic acid, butyric acid, tartaric acid, and
valeric acid. In some embodiments, the salt is a zinc salt of an
acid selected from the group consisting of acetic acid, citric
acid, lactic acid, propionic acid, butyric acid, tartaric acid, and
valeric acid.
[0239] In embodiments, the pH controller is soluble in the one or
more fatty acids used in the precursor solution.
[0240] Hydrocarbon Solvent
[0241] Any suitable C12 to C20 hydrocarbons can be used in the
precursor solution. In some embodiments, the C12 to C20
hydrocarbons in the precursor solution can include one or more
hydrocarbons selected from hexadecene, octadecene, eicosene,
hexadecane, octadecane and icosane.
[0242] In some some embodiments, tributylphosphine (TBP) is used as
a solvent in the precursor solution. In other embodiments, a
mixture of TBP and C12 to C20 hydrocarbons are used in the
precursor solution. In these embodiments, including TBP can be
advantageous because it provides a strong dipole moment, which can
aid in dissolving the Group VI elements. In many embodiments, the
precursor solution solvents can be chosen as required by the
physical properties of the materials used in the precursor solution
and as required by the apparatus available for synthesis.
[0243] Fatty Acid
[0244] Any suitable fatty acid can be used in the precursor
solution. In some embodiments, the fatty acids used in the
precursor solution can be one or more fatty acids selected from
myristoleic acid, palmitoleic acid, sapienic acid, oleic acid,
elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid,
.alpha.-Linolenic acid, arachidonic acid, eicosapentaenoic acid,
erucic acid, docosahexaenoic acid, stearic acid, palmitic acid, and
arachidic acid.
[0245] In a particular embodiment of the invention, the fatty acid
is oleic acid.
[0246] In particular embodiments, the II-VI-VI SCN precursor is
prepared by dissolving the Group II element, the first Group VI
element, and the second Group VI element in a solvent that includes
the pH controller, octadecene and a fatty acid to provide the
II-VI-VI SCN precursor solution.
[0247] In other embodiments, the II-VI-VI SCN precursor is prepared
by preparing a first solution by dissolving the Group II element
and the first Group VI element in a first solvent that includes
octadecene and a fatty acid; preparing a second solution by
dissolving the second Group VI element in a second solvent that
includes octadecene; mixing the first and second solutions to
provide a II-VI-VI SCN precursor solution. In this embodiment, both
of the first and second solutions include the pH controller.
[0248] In additional embodiments, the II-VI-VI II-VI-VI SCN
precursor is made by preparing a first solution by dissolving a
Group II element in a first solvent that includes octadecene and a
fatty acid; preparing a second solution by dissolving a first Group
VI and a second Group VI element in a second solvent that includes
octadecene; and mixing the first and second solutions to provide a
II-VI-VI SCN precursor solution. In this embodiment, both of the
first and second solutions include the pH controller.
[0249] In further embodiments, the II-VI-VI SCN precursor is
prepared by preparing a first solution by dissolving a Group II
element in a first solvent that includes octadecene and a fatty
acid; preparing a second solution by dissolving a first Group VI
element in a second solvent that includes octadecene; preparing a
third solution by dissolving a second Group VI element in a third
solvent that includes tributylphosphine; and mixing the first,
second, and third solutions to provide a II-VI-VI SCN precursor
solution. In this embodiment, one or more of the first, second and
third solutions include the pH controller.
[0250] In all of the embodiments described above, the II-VI-VI
semiconductor nanocrystals are synthesized by heating the II-VI-VI
SCN precursor solution to a temperature sufficient to form the
desired quantum dot core. In embodiments, the precursor solution
temperature is at least 200.degree., in some cases at least
225.degree., in many cases at least 250.degree. and in many
instances at least 270.degree. C. and can be up to about
400.degree., in some cases up to about 350.degree. and in other
cases up to about and 330.degree. C. The temperature at which the
II-VI-VI semiconductor nanocrystals are grown will vary depending
on the particular Group II and Group VI elements and ratios used as
well as the solvents, fatty acids and pH controller employed.
[0251] In all of the embodiments described above, the II-VI-VI
semiconductor nanocrystals are synthesized by heating the II-VI-VI
SCN precursor solution to a temperature described above for a
period of time that is at least sufficient to form the desired
quantum dot core. In some embodiments, the reaction time is at
least 40, in some cases at least 50, in many cases at least 60 and
in many instances at least 70 minutes and can be up to about 120,
in some cases up to about 110 and in other cases up to about 100
minutes. The reaction time over which the II-VI-VI semiconductor
nanocrystals are grown will vary depending on the temperature, the
particular Group II and Group VI elements and ratios used as well
as the solvents, fatty acids and pH controller employed.
[0252] In a particular embodiment of the invention, the quantum dot
core can be prepared by selecting Group II elements that are
soluble in the fatty acid. Non-limiting examples of suitable fatty
acids being stearic acid and oleic acid. The pH controller soluble
in the fatty acid, an oxide or acetate of a Group II element, is
used. The source of the Group VI elements are chosen such that they
are soluble in an organic solvent that is miscible with the fatty
acid used to dissolve the Group II. In this embodiment, the organic
solvent can be tributylphosphine and/or octadecene.
[0253] In this embodiment, the pH, or electrical environment of the
reaction system is determined by introducing the pH controller into
the reaction system. The pH controller is selected based on having
a negative or positive charge depending on the desired type of
nanocrystal and the properties of precursors being used; and are
miscible with the reaction system employed. In particular
embodiments, the pH controller is Zinc acetate.
[0254] Further to this embodiment, once the pH controller,
solvents, and elements are selected, solutions of the elements are
prepared in aliquots that are mixed together for nanocrystal
synthesis. After mixing, the reaction is allowed to go to
completion.
[0255] In this embodiment, the emission maximum is determined by 1)
the molar ratio of the two group six elements; and 2) the
concentration of PH controller.
[0256] The present invention provides methods of tuning a quantum
dot core. The inventive, convenient method for tuning the emission
maximum wavelength of the resulting quantum dot cores includes
identifying a desired emission maximum. Once a specific wavelength
is identified, a few synthesis reactions varying the molar ratios
of the precursors and the concentration of the pH controller can be
performed to identify the molar ratios of the elements and
concentration of pH controller that provide the desired wavelength.
In many some embodiments, a calibration curve can be constructed by
performing the synthesis reactions outlined above using different
ratios of elements and concentrations of pH controller. Once the
calibration curve is constructed, the ratios of elements and
concentration of pH controller can be identified for any desired
emission maximum.
[0257] Particular advantages to some of the embodiments of the
present invention include not having to rely on a particular
reaction time. Once the pH controller and stock solutions are
prepared, aliquots of each can be mixed together and stirred at a
temperature sufficient to support crystal growth, in many
embodiments from about 200.degree. C. to about 400.degree. C., for
about 40 to about 120 minutes. Advantageously, it is not important
to end the reaction at a specific time. Once the method according
to the invention is followed and the reaction is complete the
solution can continue to be stirred at growth temperatures without
altering the final quantum dot core product. In many prior art
methods of synthesizing nanocrystals, an additional 1 to 5 seconds
of extra reaction time substantially alters the product.
[0258] In particular embodiments, the semiconductor materials of
the quantum dot cores may have a gradient of one or more of the
semiconductor materials radiating from the center of the
nanocrystal or quantum dot to the outermost surface of the
nanocrystal. Such nanocrystals or quantum dots are referred to
herein as "concentration-gradient quantum dots." For example, in
some embodiments, a concentration-gradient quantum dot having at
least a first semiconductor and a second semiconductor may be
prepared such that the concentration of the first semiconductor
gradually increases from the center of the concentration-gradient
quantum dot to the surface of the quantum dot. In such embodiments,
the concentration of the second semiconductor can gradually
decrease from the core of the concentration-gradient quantum dot to
the surface of the quantum dot. Without wishing to be bound by
theory, concentration-gradient quantum dot may have a band gap
energy that is non-linearly related to the molar ratio of the at
least two semiconductors.
[0259] Concentration-gradient quantum dots may be prepared from any
semiconductor material known in the art including those
semiconductor materials listed above, and concentration-gradient
quantum dots may be composed of two or more semiconductor
materials. In particular embodiments, concentration-gradient
quantum dots may be alloys of CdSeTe having a molecular formula
CdS1-xTex, CdSSe having a molecular formula CdS1-xSex, CdSTe having
a molecular formula CdS1-x Tex, ZnSeTe having a molecular formula
ZnSe1-x Tex, ZnCdTe having a molecular formula Zn1-x CdxTe, CdHgS
having a molecular formula Cd1-x HgxS, HgCdTe having a molecular
formula HgCdTe, InGaAs having a molecular formula InGaS, GaAlAs
having a molecular formula GaAlAs, or InGaN having a molecular
formula InGaN, where x in each example can be any fraction between
0 and 1.
[0260] The methods described above provide various uncapped
semiconductor nanocrystals, referred to collectively as quantum dot
cores herein.
[0261] Some embodiments provide quantum dot cores and in particular
II-VI-VI semiconductor nanocrystals made according to the methods
described above.
[0262] Some embodiments provide quantum dot cores and II-VI-VI
semiconductor nanocrystal that include Cd, S and Se, where the
nanocrystal has been modified by a zinc alkylcarboxylate (such as
zinc acetate). The quantum dot cores and II-VI-VI semiconductor
nanocrystals generally correspond to the formula WYxZ(1-x) where W
is a Group II element, Y and Z are different Group VI elements, and
0<X<1. In particular embodiments, the quantum dot cores and
II-VI-VI semiconductor nanocrystals have a predetermined emission
wavelength.
[0263] The II-VI-VI semiconductor nanocrystals of the invention can
have any diameter, and, thus, be of any size, provided that quantum
confinement is achieved. In certain embodiments, the II-VI-VI
semiconductor nanocrystals described herein have a primary particle
size of less than about 10 nm in diameter. According to other
embodiments, the II-VI-VI semiconductor nanocrystals have a primary
particle size of between about 1 to about 500 nm in diameter. In
other embodiments, a primary particle size of between about 1 to
about 100 nm in diameter, and in still other embodiments, a primary
particle size of between about 5 to about 15 nm in diameter. As
used herein, the phrase "primary particle" refers to the smallest
identifiable subdivision in a particulate system. Primary particles
can also be subunits of aggregates.
[0264] Standard Core/Shell Quantum Dots (CdSe/ZnS)
[0265] Standard core/shell quantum dots of the CdSe/ZnS variety
were obtained from a commercial source. The quantum dots were
processed to assess the stability of the quantum dots with and
without an Al2O3 passivation layer, and the stability of the
quantum dots with and without the Al2O3 passivation layer
additionally with an without incorporation into the polymer matrix
described herein. FIG. 6 depicts the results of those tests.
[0266] To assess the effect of the Al2O3 passivation layer, QDs
with and without the Al2O3 passivation layer were coated naked on
glass slides and exposed to 85/85 conditions (85.degree. C., 85%
humidity.) There was a marked difference as seen in FIG. 6 between
Al2O3 passivated QDs and those that without the Al2O3 passivation.
The relative intensity is not necessarily important in this
analysis, but the drop in the intensity of the QDs without Al2O3
passivation layer indicates a much less stable QD.
[0267] FIG. 6 shows that a core/shell QD with or without the Al2O3
passivation layer benefits from incorporation in the polymer as
described below herein. Here, QDs with and without the passivation
layer were dispersed and embedded in the polymer described herein
and tested under the 85/85 test conditions. FIG. 6 shows that the
dispersion in the polymer lead to stable QDs for both samples.
Thus, dispersion within the polymer as disclosed herein leads to
stable QDs.
[0268] Shell Growth (Capping) of Cd-Free Nanoparticle Cores
[0269] Capping the purified Cd-free nanoparticle cores can be
accomplished by the following methods.
[0270] Method 1:
[0271] Maintaining an oxygen free environment during the capping
process. Take a sample of the purified Cd-free nanoparticle cores
and perform the steps below. The quantities indicated are for every
0.1 mmol of Group II element in the Cd-free nanoparticle core
solution.
[0272] 1) Vacuum purging until the nonpolar solvent has
evaporated.
[0273] 2) Adding 4.00 g trioctylphosphine oxide, and vacuum purging
for 10 minutes. Optionally, 0.2 g stearic acid can be added along
with the trioctylphospine oxide prior to performing the vacuum
purge, if a shell comprising stearic acid is desired.
[0274] 3) Heating to about 100.degree. C. for about 30 minutes
under vacuum and then to 200.degree. C. without vacuum for 30
minutes.
[0275] 4) Preparing a capping solution by mixing 40 .mu.L Zn(CH3)2,
80 .mu.L Hexamethyldisilathiane (CAS#3385-94-2), and 2.00 mL
trioctylphosphine in an oxygen-free environment.
[0276] 5) Dripping the capping solution into solution (3) at about
200-220.degree. C. over about 5 minutes for every 2.0 mL
trioctylphosphine used.
[0277] 6) Stirring for about 30 minutes to about 2 hours at
200.degree. C. under nitrogen.
[0278] 7) Allowing the solution to cool to room temperature.
[0279] A graph of ratios of elements versus emission wavelength can
be prepared to provide a calibration curve. The calibration curve
can be used to determine the proper fraction of elements needed to
obtain crystals that fluoresce at the desired wavelength.
[0280] Method 2:
[0281] Load purified Cd-free nanoparticle cores into a three-neck
flask with desired amounts of Zinc Acetate, elemental sulfur,
1-dodecanethiol, octadecane and octanoic acid. Degassing for 20
about minutes, then filling the flask with nitrogen, raising the
temperature high enough to allow the reaction to proceed for about
60 minutes at that temperature.
[0282] Capping the Quantum Dot Core
[0283] Embodiments of the present invention relate to a method of
capping a semiconductor nanocrystal. Any of the quantum dot cores
disclosed hereinabove can be used in the methods according to these
embodiments. One or more of the semiconductor nanocrystals
described above are provided and heated in a solution containing
one or more C12 to C20 hydrocarbons and one or more fatty acids to
form an SCN solution. A solution containing dialkyl zinc,
hexaalkyldisilathiane and trialkylphosphine is added to the SCN
solution and heated to a temperature sufficient to produce a capped
II-VI-VI semiconductor nanocrystal.
[0284] In particular embodiments, a predetermined emission
wavelength from the capped semiconductor nanocrystal is identified
and an amount of pH controller may be added to provide the
predetermined emission wavelength from the capped semiconductor
nanocrystal.
[0285] In some embodiments, the amount of pH controller is selected
to tune the emission maximum wavelength of the capped SCN. When a
specific wavelength is desired, a few synthesis reactions using
different concentrations of pH controllers and the particular SCN
to be capped are run to construct a calibration curve. The required
concentration of pH adjuster is then identified for the desired
wavelength from the calibration curve.
[0286] In particular aspects of this embodiment, the emission
wavelength from the capped semiconductor nanocrystal when no pH
controller is present can be any wavelength in the visible range
and in particular from about 400 nm to about 700 nm and any
wavelength between those values. When the pH controller is included
in the SCN solution, the emission wavelength of the capped
semiconductor nanocrystal shifts to a longer wavelength. In some
aspects of the invention, the SCN emission wavelength can increase
at least 2 nm, in some case at least 3 nm and in other cases at
least 4 nm and can increase up to 15, in some cases up to 12 and in
other cases up to 10 nm for each 0.1 weight percent of pH
controller included in the SCN solution. The amount of capped
semiconductor nanocrystal emission wavelength can increase and can
be any value or range between any of the values recited above. The
amount of capped semiconductor nanocrystal emission wavelength can
increase and vary based on the size of the capped semiconductor
nanocrystal, the particular pH adjuster used and the particular
Group II and Group VI elements used.
[0287] The pH controller is included in the SCN solution at a level
that provides the desired capped semiconductor nanocrystal emission
wavelength increase, often referred to as "tuning" the capped
semiconductor nanocrystal. The pH controller can be present in the
SCN solution at a level of from about 0.01, in some cases about
0.1, in other cases about 0.15 and in some instances about 0.2
weight percent of the SCN solution and can be up to about 1, in
some cases up to about 0.9, in other cases up to about 0.8 and in
some instances up to about 0.7 weight percent of the SCN solution.
The amount of pH controller will be an amount sufficient to achieve
the desired tuning and will typically not exceed an amount that
will increase the capped semiconductor nanocrystal emission
wavelength beyond the visible spectrum. The amount of pH controller
in the SCN solution can be any value or range between any of the
values recited above.
[0288] Any pH controller that can maintain a desired pH and effect
the emission wavelength tuning described above can be used in the
SCN solution. In some embodiments, the pH controller can be an
oxide or carboxylic acid salt of a Group II element. In particular
embodiments the pH controller can be selected from zinc salts of
acetic acid, citric acid, lactic acid, propionic acid, butyric
acid, tartaric acid, and valeric acid. In particular embodiments,
the pH controller is an oxide or carboxylic acid salt of a Group II
element.
[0289] In some aspects of the invention, the pH controller is
selected from zinc salts of acetic acid, citric acid, lactic acid,
propionic acid, butyric acid, tartaric acid, and valeric acid.
[0290] In some embodiments, the C12 to C20 hydrocarbons used in the
SCN solution can be one or more selected from hexadecene,
octadecene, eicosene, hexadecane, octadecane and Icosane.
[0291] In other embodiments, the fatty acids used in the SCN
solution can be one or more selected from myristoleic acid,
palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic
acid, linoleic acid, linoelaidic acid, .alpha.-Linolenic acid,
arachidonic acid, eicosapentaenoic acid, erucic acid,
docosahexaenoic acid, stearic acid, palmitic acid, and arachidic
acid.
[0292] In embodiments, the dialkyl zinc is dimethyl zinc, the
hexaalkyldisilathiane is hexamethyldisilathiane and the
trialkylphosphine is trioctylphosphine.
[0293] In many embodiments, the temperature the SCN solution
containing dialkyl zinc, hexaalkyldisilathiane and
trialkylphosphine is heated to in order to form the capped quantum
dot is between about 150.degree. C. and 350.degree. C.
[0294] The methods described herein above provide capped
semiconductor nanocrystals.
[0295] The capped semiconductor nanocrystals of the invention can
have any diameter, and, thus, be of any size, provided that quantum
confinement is achieved. In certain embodiments, the capped
semiconductor nanocrystals described herein have a primary particle
size of less than about 10 nm in diameter. According to other
embodiments, the II-VI-VI semiconductor nanocrystals have a primary
particle size of between about 1 to about 500 nm in diameter. In
other embodiments, a primary particle size of between about 1 to
about 100 nm in diameter, and in still other embodiments, a primary
particle size of between about 5 to about 15 nm in diameter. As
used herein, the phrase "primary particle" refers to the smallest
identifiable subdivision in a particulate system. Primary particles
can also be subunits of aggregates.
[0296] Cd-Free Al2O3 Capping
[0297] In some embodiments a passivation layer is applied to a
capped Cd-free nanoparticle core prepared as described above. In
these embodiments, an aluminum capping material is prepared by
mixing trimethylaluminum and trioctylphosphine to form a capping
solution. The capping solution is added to a solution of core/shell
Cd-free nanoparticles at a temperature sufficient to grow
monolayers of aluminum on the surface of the core/shell Cd-free
nanoparticles to provide aluminum coated core/shell Cd-free
nanoparticle cores. In particular embodiments, the monolayers can
be from at least 1 atom thick, in some cases at least two atoms
thick and in other cases at least 3 atoms thick and can be up to 20
atoms thick, in some cases up to 15 atoms thick, in other cases up
to 10 atoms thick and in some instances up to 5 atoms thick. In
many instances the capping solution is mixed with the solution of
capped Cd-free nanoparticle cores at a temperature of from
100.degree. C., in some cases at least 150.degree. C. and in other
cases at least 175.degree. C. and can be mixed at a temperature up
to about 300.degree. C., in some cases up to about 250.degree. C.
and in other cases up to about 225.degree. C. The aluminum coated
capped Cd-free nanoparticle cores are then allowed stand in air at
a temperatures of less than 100.degree. C. to oxidize for a time
sufficient to convert all or some of the monolayers of aluminum to
monolayers of Al2O3, providing aluminum oxide coated capped Cd-free
nanoparticle cores ("passivated core/shell Cd-free
nanoparticles").
[0298] The fabrication methods for the passivated core/shell
Cd-free nanoparticles may be further modified in some embodiments
to achieve desired features. For example, nanoparticle
characteristics such as surface functionality, surface charge,
particle size, zeta (.zeta.) potential, hydrophobicity, and the
like, may be optimized depending on the particular application of
the passivated nanocrystals. For example, in some embodiments,
modified surface chemistry and small particle size may contribute
to reduced clearance of the nanoparticles. In other embodiments,
the passivated nanoparticles are stable in water or other liquid
medium without substantial agglomeration and substantial
precipitation for at least 30 days, preferably for at least 90
days, and more preferably for at least 120 days. The term "stable"
or "stabilized" means a solution or suspension in a fluid phase
wherein solid components (i.e., nanoparticles) possess stability
against aggregation and agglomeration sufficient to maintain the
integrity of the compound and preferably for a sufficient period of
time to be useful for the purposes detailed herein. As used herein,
the term "agglomeration" refers to the formation of a cohesive mass
consisting of particulate subunits held together by relatively weak
forces (for example, van der Waals or capillary forces) that may
break apart into particulate subunits upon processing, for example.
The resulting structure is called an "agglomerate."
[0299] The passivated core/shell Cd-free nanoparticles can have any
diameter, and, thus, be of any size, provided that quantum
confinement is achieved. In certain embodiments, the passivated
core/shell Cd-free nanoparticles described herein have a primary
particle size of less than about 10 nm in diameter. According to
other embodiments, the passivated core/shell Cd-free nanoparticles
have a primary particle size of between about 1 nm to about 500 nm
in diameter. In other embodiments, a primary particle size of
between about 1 to about 100 nm in diameter, and in still other
embodiments, a primary particle size of between about 5 nm to about
15 nm in diameter. As used herein, the phrase "primary particle"
refers to the smallest identifiable subdivision in a particulate
system. Primary particles can also be subunits of aggregates.
[0300] Passivating a Capped II-VI-VI Semiconductor Nanocrystal
(e.g. Al2O3 Passivation)
[0301] In some embodiments a passivation layer is applied to a
capped II-VI-VI semiconductor nanocrystal prepared as described
above. In these embodiments, an aluminum capping material is
prepared by mixing trimethylaluminum and trioctylphosphine to form
a capping solution. The capping solution is added to a solution of
core/shell nanocrystals at a temperature sufficient to grow
monolayers of aluminum on the surface of the core/shell
nanocrystals to provide aluminum coated core/shell nanocrystals. In
particular embodiments, the monolayers can be from at least 1, in
some cases at least two and in other cases at least 3 atoms thick
and can be up to 20, in some cases up to 15, in other cases up to
10 and in some instances up to 5 atoms thick. In many instances the
capping solution is mixed with the solution of capped II-VI-VI
semiconductor nanocrystal at a temperature of from 100, in some
cases at least 150 and in other cases at least 175.degree. C. and
can be mixed at a temperature up to about 300, in some cases up to
about 250 and in other cases up to about 225.degree. C. The
aluminum coated capped II-VI-VI semiconductor nanocrystal are then
allowed stand in air at temperatures less than 100.degree. C. and
oxidize for a time sufficient to convert the all or some of the
monolayers of aluminum to monolayers of Al2O3, to provide aluminum
oxide coated capped II-VI-VI semiconductor nanocrystal ("passivated
core/shell nanocrystals").
[0302] The fabrication methods for the passivated nanocrystals of
the invention may be further modified in some embodiments to
achieve desired features. For example, nanoparticle characteristics
such as surface functionality, surface charge, particle size, zeta
(.zeta.) potential, hydrophobicity, and the like, may be optimized
depending on the particular application of the passivated
nanocrystals. For example, in some some embodiments, modified
surface chemistry and small particle size may contribute to reduced
clearance of the nanoparticles. In other embodiments, the
passivated nanoparticles are stable in water or other liquid medium
without substantial agglomeration and substantial precipitation for
at least 30 days, preferably for at least 90 days, and more
preferably for at least 120 days. The term "stable" or "stabilized"
means a solution or suspension in a fluid phase wherein solid
components (i.e., nanoparticles) possess stability against
aggregation and agglomeration sufficient to maintain the integrity
of the compound and preferably for a sufficient period of time to
be useful for the purposes detailed herein. As used herein, the
term "agglomeration" refers to the formation of a cohesive mass
consisting of particulate subunits held together by relatively weak
forces (for example, van der Waals or capillary forces) that may
break apart into particulate subunits upon processing, for example.
The resulting structure is called an "agglomerate."
[0303] The passivated capped nanocrystals of the invention can have
any diameter, and, thus, be of any size, provided that quantum
confinement is achieved. In certain embodiments, the passivated
nanocrystals described herein have a primary particle size of less
than about 10 nm in diameter. According to other embodiments, the
passivated nanocrystals have a primary particle size of between
about 1 to about 500 nm in diameter. In other embodiments, a
primary particle size of between about 1 to about 100 nm in
diameter, and in still other embodiments, a primary particle size
of between about 5 to about 15 nm in diameter. As used herein, the
phrase "primary particle" refers to the smallest identifiable
subdivision in a particulate system. Primary particles can also be
subunits of aggregates.
[0304] Particular embodiments described above provide a capped
II-VI-VI semiconductor nanocrystal that includes a core that
includes a II-VI-VI semiconductor nanocrystal containing Cd, S and
Se, where the nanocrystal has been modified by a zinc
alkylcarboxylate and a cap layer selected from a layer containing
ZnS, a layer containing Al2O3, and a layer containing ZnS and a
second layer containing Al2O3.
[0305] As a non-limiting more particular description of the capped
semiconductor nanocrystals according to the invention the source of
the various elements should be soluble in a fatty acid such as
stearic acid or oleic acid. As a non-limiting example, an oxide or
acetate compound of the group two elements are often soluble in
stearic acid. The source of both group VI elements should be chosen
such that they are soluble in an organic solvent that is miscible
with the fatty acid used to dissolve the group two element. Pure
group six elements in powder form are often suitable.
Tributylphosphine (TBP) and octadecene are examples of solvents
that are miscible with oleic acid. In many embodiments, TBP
provides a strong dipole moment, if needed, to dissolve the group
six element. The solvents should be chosen as required by the
physical properties of the elements and as required by the
apparatus available for synthesis.
[0306] In many embodiments, the pH, or electrical environment of
the reaction system is determined by introducing additional
materials to the reaction system. These materials should 1) have a
negative or positive charge depending on the type of nanocrystal
desired and the properties of precursors used; and 2) are mixable
with the chosen reaction system. In particular embodiments, Zinc
acetate is the pH controller.
[0307] Continuing with this embodiment, it is important to remember
that the method according to the invention does not require timing
of a critical end point. The reaction can be allowed to go to
completion. The emission maximum is determined by 1) the molar
ratio of the two group six elements; and 2) the concentration of
the pH controller, not the reaction time.
[0308] Further to this embodiment and the description above, tuning
the emission maximum wavelength to a specific desired wavelength
requires only a few synthesis reactions using different molar
ratios of precursors and concentrations of pH controllers. This
allows for fine tuning the molar ratios and the concentration of pH
controllers to the desired wavelength.
[0309] In embodiments, a calibration curve is generated by
performing a number of syntheses using different concentrations of
PH controller. Stock solutions of pH controller are prepared and
aliquots of each are mixed together and stirred at a high enough
temperature to support crystal growth. Suitable temperatures can be
between about 200.degree. C. and about 400.degree. C. for about 40
to about 120 minutes. It is not important to end the reaction at a
specific time. In embodiments, once the reaction is complete the
solution can be stirred at growth temperatures without altering the
product. As a non-limiting example, stirring at growth temperatures
for 10, 20, and 30 minutes at temperature does not change the end
product semiconductor nanocrystals when a CdSeS system is used. As
indicated above, prior art methods of nanocrystal synthesis where
1-5 seconds of extra reaction time is employed substantially alters
the product.
[0310] The method of this embodiment produces uncapped
semiconductor nanocrystals, referred to as "cores". Capping the
cores makes them more stable and increases their quantum
efficiency. As a non-limiting example, capping with ZnS is known to
those skilled in the art. Prior to capping the cores of this
embodiment, it is helpful, though not required, to purify the
crystals.
[0311] The cores according to this embodiment can be purified by
first diluting the synthesis mixture to 7.5 times its volume with a
1:3 mixture of hexane and butanol. This causes the nanocrystals to
precipitate which can then be pelletized via centrifugation. The
crystals are then washed three times by first suspending the
crystals in hexane and then adding three times the volume of
methanol, which causes the crystals to re-precipitate. After the
final wash, the crystals are dissolved in hexane for capping.
[0312] Other particular embodiments provide a method of providing
capped CdSeS cores. The method includes three steps; core
synthesis, core purification, and core capping.
[0313] The particular core synthesis of this embodiment
includes:
[0314] 1A) Preparing a desired amount of pH controller and
precursor by mixing the pH controller and precursor with octadecene
and a fatty acid (oleic acid and/or stearic acid), thoroughly
sparging with nitrogen gas, and heating to about 250-350.degree. C.
until the solution is clear.
[0315] 2A) Preparing solutions of sulfur and selenium in an oxygen
free environment and mixing aliquots of each mixed to achieve the
desired fluorescent wavelength, so that when added to the cadmium
precursor solution the molar ratios of Cd:S:Se are 2:X:(1-X), where
0<X<1.
[0316] 3A) Combining the mixture of sulfur and selenium with
octadecene to about 45-50 volume percent of the cadmium precursor
solution while maintaining an oxygen free environment.
[0317] 4A) Injecting the solution from step (3A) into solution from
step (1A) at 250-350.degree. C. and then maintain a temperature of
from about 250-350.degree. C. The resulting solution is stirred
about 40-120 minutes, until the reaction is complete, while
maintaining an oxygen free environment.
[0318] The resulting cores are purified according to this
particular embodiment using the following method:
[0319] 1B) Transferring the core synthesis solution from step (4A)
to a centrifuge tube and diluting to 7.5 times its volume with a
1:3 mixture of hexane and butanol.
[0320] 2B) Centrifuging the mixture from (1B) until crystal pellets
are formed and pouring off the supernatant.
[0321] 3B) Washing the crystal pellets from step (2B) three times
with 1:3 hexane:methanol, using about 6.5 times the volume of the
original core synthesis solution for each wash. Adding hexane to
the suspend crystals and then adding methanol to precipitate the
crystals.
[0322] 4B) Suspending the precipitated crystals from step (3B) in
hexane at about 75-85% of the volume of the synthesis solution.
[0323] The resulting purified cores are capped according to this
particular embodiment by maintaining an oxygen free environment
during the capping process and taking a sample of the purified
cores from step (4B) and using the following method (The quantities
indicated are used with about 0.1 mmol of cadmium in the core
solution in step (4B)):
[0324] 1C) Vacuum purging until substantially all of the hexane has
evaporated.
[0325] 2C) Adding about 0.2 g of Zinc Acetate (pH controller), 10
ml of octadecene and a fatty acid, and vacuum purging for 10
minutes.
[0326] 3C) Heating to about 75-125.degree. C. for about 30 minutes
and then to about 175-225.degree. C. for about 30 minutes.
[0327] 4C) Preparing a capping solution by mixing about 35-45 .mu.L
Zn(CH3)2, about 75-85 .mu.L Hexamethyldisilathiane (CAS#3385-94-2),
and about 1.85-2.15 mL trioctylphosphine in an anaerobic
environment.
[0328] 5C) Slowly adding the capping solution of step (4C) into the
solution of step (3C), over a period of about 4-6 minutes for every
2.0 mL trioctylphosphine used.
[0329] 6C) Stirring the solution from step (5C) for about 1.5-2.5
hours at 175-225.degree. C. under nitrogen.
[0330] 7C) Allowing the solution from (6C) to cool to room
temperature.
[0331] Polymer Containing the Capped Quantum Dot Core
[0332] As used herein, the term "acrylate" is meant to include
esters of both acrylic and methacrylic acid, such as the
corresponding alkyl esters often referred to as acrylates and
methacrylates, and other esters which may contain one or more of N,
P, Si and S, which the term "acrylate" is meant to encompass.
Acrylates, as used herein, have the formula:
##STR00003##
[0333] wherein R.sub.1, is hydrogen or methyl; and
[0334] R.sub.2 is selected from the group consisting of methyl;
ethyl; propyl; dodecyl; steryl; isopropyl; butyl; isobutyl; pentyl;
cyclopentyl; isopentyl; linear C.sub.1-18 alkyl; linear, branched,
and cyclic C.sub.6-8 alkyl.
[0335] As used herein, the term "acrylate resin" refers to polymers
resulting from the polymerization of one or more acrylates and
optionally one or more other polymerizable unsaturated molecules
together with any (non-quantum dot) additives that may be blended
into the polymer.
[0336] Unless otherwise specified, all molecular weight values are
determined using gel permeation chromatography (GPC) using
appropriate polystyrene standards. Unless otherwise indicated, the
molecular weight values indicated herein are weight average
molecular weights (Mw).
[0337] Various embodiments are directed to polymers, resins, films
or 3-D structures that contain semiconductor nanocrystals as
described above dispersed in an acrylate resin. Any suitable
acrylate resin can be used in the invention. A non-limiting example
of suitable acrylate resins include those that include repeat or
monomer units derived from polymerizing one or more monomers
according to the formula:
##STR00004##
wherein R.sup.1 is hydrogen or methyl and
[0338] R.sup.2 is selected from the group consisting of methyl;
ethyl; propyl; dodecyl; steryl; isopropyl; butyl; isobutyl; pentyl;
cyclopentyl; isopentyl; linear containing from 1-18 Carbon atoms,
branched and cyclic hexyl; linear, branched and cyclic heptyl; and
linear branched and cyclic octyl.
[0339] Compounds of formula I are referred to herein as acrylate
monomers.
[0340] The amount and type of the acrylate monomers in the acrylate
resin is determined based on the desired properties of the
resulting film and/or 3-D structure or other product and the
particular semiconductor nanocrystals used in the film.
[0341] In some embodiments, the acrylate resin is made from methyl
methacrylate (i.e. R1=R2=methyl) and, optionally, one or more other
monomers according to structure I. In this embodiment, the amount
of methyl methacrylate can be at least 1%, in some cases at least
5%, in other cases at least 10%, in some instances at least 20% and
in other instances at least 25% and can be 100%, in some cases up
to 95%, in other cases up to 90%, in some instances up to 80%, in
other instances up to 70%, in some situations up to 60% and in
other situations up to 50% based on the weight of the acrylate
resin. The amount of methyl methacrylate in the acrylate resin can
be any value or range between any of the values recited above.
[0342] In some embodiments, the acrylate resin is made from methyl
acrylate (i.e. R1=H, R2=methyl) and, optionally, one or more other
monomers according to structure I. In this embodiment, the amount
of methyl acrylate can be at least 1%, in some cases at least 5%,
in other cases at least 10%, in some instances at least 20% and in
other instances at least 25% and can be 100%, in some cases up to
95%, in other cases up to 90%, in some instances up to 80%, in
other instances up to 70%, in some situations up to 60% and in
other situations up to 50% based on the weight of the acrylate
resin. The amount of methyl acrylate in the acrylate resin can be
any value or range between any of the values recited above.
[0343] The amount of methyl methacrylate and/or methyl acrylate in
the acrylate resin is determined based on the desired properties of
the resulting film or structure and the particular capped or capped
and passivated semiconductor nanocrystals used in the film.
[0344] In these embodiments, the other acrylate monomer(s) are used
at a level that brings the total percentage of monomers used in the
acrylate resin to 100%.
[0345] In particular some embodiments, the acrylate resin is made
from cyclohexyl acrylate (i.e. R1=H, R2=cyclohexyl) and,
optionally, one or more other monomers according to structure I. In
this embodiment, the amount of cyclohexyl acrylate can be at least
1%, in some cases at least 5%, in other cases at least 10%, in some
instances at least 20% and in other instances at least 25% and can
be 100%, in some cases up to 95%, in other cases up to 90%, in some
instances up to 80%, in other instances up to 70%, in some
situations up to 60% and in other situations up to 50% based on the
weight of the acrylate resin. The amount of cyclohexyl acrylate in
the acrylate resin can be any value or range between any of the
values recited above. In these embodiments, the other acrylate
monomer(s) are used at a level that brings the total percentage of
monomers used in the acrylate resin to 100%. The amount of
cyclohexyl acrylate in the acrylate resin is determined based on
the desired properties of the resulting film or structure and the
particular capped or capped and passivated semiconductor
nanocrystals used in the film.
[0346] Other embodiments are directed to films and 3-D structures
that contain semiconductor nanocrystals as described above
dispersed in polymers derived from polymerizing one or more
acrylate monomers of formula I with one or more monomers according
to following formulae:
##STR00005##
wherein
[0347] each of R3 and R4 in structures II through V, is
independently selected from methyl, ethyl, propyl, isopropyl,
butyl, isobutyl, pentyl, cyclopentyl, isopentyl, C6 to C12 linear,
branched, cyclic and aromatic hydrocarbyl, and polyethylene glycol;
and
[0348] R5 is selected from of hydrogen, methyl, ethyl, propyl,
isopropyl, butyl, isobutyl, pentyl, cyclopentyl, isopentyl C6 to
C12 linear, branched, cyclic and aromatic hydrocarbyl, and
polyethylene glycol.
[0349] Monomers of Formulae II-V are referred to herein as nitrogen
containing monomers.
[0350] In particular embodiments, the acrylate resin is made from
one or more acrylate monomers and one or more nitrogen containing
monomers. In this embodiment, the amount of acrylate monomer can be
at least 1%, in some cases at least 5%, in other cases at least
10%, in some instances at least 20% and in other instances at least
25% and can be up to 99%, in some cases up to 95%, in other cases
up to 90%, in some instances up to 80%, in other instances up to
70%, in some situations up to 60% and in other situations up to 50%
based on the weight of the acrylate resin. The amount and type of
acrylate monomer and the corresponding amount and type of nitrogen
containing monomers in the acrylate resin can be any value or range
between any of the values recited above. In these embodiments, the
nitrogen containing monomers are used at a level that brings the
total percentage of monomers used in the acrylate resin to 100%.
The amount and type of acrylate monomer and the amount and type of
nitrogen containing monomer in the acrylate resin is determined
based on the desired properties of the resulting film and the
particular capped or capped and passivated semiconductor
nanocrystals used in the film.
[0351] Other embodiments are directed to films and 3-D structures
that contain capped or capped and passivated 2-6-6 semiconductor
nanocrystals as described above dispersed in polymers derived from
polymerizing one or more acrylate monomers according structure I
and one or more nitrogen containing monomers according to one or
more of structures II, III, IV and V.
[0352] In some embodiments, the films and 3-D structures described
herein can be prepared using any suitable method. A non-limiting
example of preparing the films and 3-D structures described herein
include dispersing the capped nanocrystals in a suitable solution
of polymers derived from polymerizing one or more acrylate monomers
according structure I and/or one or more nitrogen containing
monomers according to one or more of structures II, III, IV and V.
Typically an organic solvent is used in the polymer solution. Any
good solvent for the polymers can be used, however, solvents that
can be removed to promote film formation are often used. Suitable
solvents include, but are not limited to C6-C20 linear, branched
and cyclic aliphatic and aromatic solvents. In particular
embodiments, hexane, octane, decene, benzene, toluene, and xylene
are suitable solvents. The solution of capped nanocrystals,
polymer, and solvent is typically homogenized to uniformly disperse
the capped nanocrystals in the polymer solution and then drawn into
a film, and the solvent allowed to evaporate.
[0353] In some embodiments, the nanocrystal/polymer composite
described herein typically contain nanocrystals at a level of at
least 0.0001 wt %, in some cases at least 0.01 wt %, in other cases
at least 0.1 wt %, in some instances at least 1 wt %, and in other
instances at least 5 weight percent of nanocrystals to composite
and can contain up to about 75%, in some cases about 60%, in other
cases about 50%, in some instances about 40% and in other instances
about 30% weight percent nanocrystals to composite. The amount of
nanocrystals will depend on the intended end use, the particular
nanocrystals used as well as the particular polymer used. The
amount of nanocrystals in the nanocrystal/polymer composite can be
any value or range between any of the values recited above, (e.g.
0.0001 to 75% by weight of the composite).
[0354] The nanocrystal/polymer composite of the current invention,
may also contain additives, such as for example, primary
antioxidants (such as hindered phenols, including vitamin E);
secondary antioxidants (such as phosphites and phosphonites);
nucleating agents, plasticizers or process aids (such as
fluoroelastomer and/or polyethylene glycol bound process aid), acid
scavengers, stabilizers, anticorrosion agents, blowing agents,
other ultraviolet light absorbers such as chain-breaking
antioxidants, etc., quenchers, antistatic agents, slip agents,
anti-blocking agent, pigments, dyes and fillers and cure agents
such as peroxide. The particular additives used are chosen so as
not to interfere with the desired properties to be obtained from
the nanocrystal/polymer composite.
[0355] These and other common additives in the composite industry
may be present in nanocrystal/polymer composite at from about 0.01
to about 50 wt % in some embodiments, and from about 0.1 to about
20 wt % in another embodiment, and from about 1 to about 5 wt % in
yet another embodiment, wherein a desirable range may include any
combination of any upper wt % limit with any lower wt % limit.
[0356] Multilayer Films and 3-D Structures Including Films and 3-D
Structures Containing the Capped Quantum Dot Core
[0357] Various embodiments are directed to multilayer films and 3-D
structures that include one or more layers that include the films
and 3-D structures containing capped or capped and passivated
quantum dot cores as described above. The quantum dot cores may be
uncapped, capped, passivated, or any combination thereof.
[0358] As a non-limiting example, FIG. 7 shows multilayer film 10
that includes first layer 12 and last layer 16 and a middle layer
14 that includes a film containing capped or capped and passivated
quantum dot cores as described above. In some embodiments, first
layer 12 and last layer 16 can have a refractive index of from at
least 1.47, in some cases at least 1.5 and in other cases at least
1.52 and can have a refractive index of up about 1.7, in some cases
up to about 1.65 and in other cases up to about 1.6.
[0359] Generally, multilayer films and 3-D structures according to
the invention as depicted in FIG. 7 can be made by first dispersing
quantum dots in a suitable solvent and dissolving a acrylate resin,
resin containing nitrogen monomers, and/or a resin made from
acrylate monomers and nitrogen containing monomers into the quantum
dot dispersion. The resulting dispersion is then coated onto a
first film, which is then dried. A second film, and any subsequent
film, is then heat laminated over the dispersion coated surface of
to the first film.
[0360] In many prior art systems, the reabsorption behavior of
quantum dots and their lack of resistance to environmental
degradation has been addressed using expensive multi-laminate
structures. These structures are used to efficiently convert blue
light from light emitting diodes ("LEDs") into longer quantum dot
emitted wavelengths ("downconversion") and to protect the quantum
dots for extended use in optoelectronic devices. Examples of such
structures include cutoff filters, dichroic layers, separation of
quantum dots into multiple single-color layers and other
complicated multilaminate structures. However, these structures are
complex and expensive to manufacture.
[0361] The invention disclosed herein, as exemplified in FIG. 7
provides a single-coat downconversion film (SCDF) that includes a
single layer 14 of a quantum dot containing matrix sandwiched
between two transparent films (12, 16) and 3-D structures, which
can be easily manufactured at low cost. A combination of maximum
dispersion and refractive index (RI) matching enables a simple and
cost effective product that, at a minimum, provides the performance
of more complicated structures. Thus, embodiments of the multilayer
films and 3-D structures according to the invention rely on a
combination of maximum quantum dot dispersion and refractive index
matching to achieve optimal performance.
[0362] Referring to FIG. 8, quantum dots in photoluminescent mode
emit light isotropically (in all possible directions). In many
applications it is desirable for the light produced by quantum dots
to escape the matrix in which they are dispersed and travel in a
preferred direction. The simplest structure to achieve some degree
of directionality is to coat a layer of quantum dots in a polymer
matrix on a film of material with a higher refractive index than
the polymer matrix. With quantum dots dispersed in first material
(20) with a lower refractive index (n1) than second material (22)
with a refractive index (n2), and with an excitation source (24)
coming from the side opposite second material (22) (i.e. through
the first material 20), a percentage of light emitted isotropically
from QDs in first material (20) will be refracted toward the normal
line and will be preferentially emitted away from the excitation
source compared to a situation where n1=n2. If a reflector is
placed behind the excitation source then with each pass of
reflected quantum dot light the quantum dot light will be directed
toward the normal line, amplifying the directionality during each
pass. If a sandwich is constructed with first material (20) having
refractive index n1 layered between two second material (22) layers
having refractive index n2, then the light is further directed
toward the normal line with each pass.
[0363] Further embodiments are shown in FIG. 9, which shows
multilayer film 50 that includes first layer 52 and last layer 56
and a middle layer 54 that includes a film containing capped or
capped and passivated quantum dot cores as described above. First
barrier layer 58 and second barrier layer 60 are situated between
middle layer 54 and first layer 52 and middle layer 54 and last
layer 56 respectively. In particular some embodiments, first layer
52 and last layer 56 can have a refractive index of from at least
1.47, in some cases at least 1.5 and in other cases at least 1.52
and can have a refractive index of up about 1.7, in some cases up
to about 1.65 and in other cases up to about 1.6.
[0364] Generally, multilayer films and 3-D structures according to
the invention as depicted in FIG. 9 can be made by first dispersing
quantum dots in a suitable solvent and dissolving a acrylate resin,
resin containing nitrogen monomers, and/or a resin made from
acrylate monomers and nitrogen containing monomers into the quantum
dot dispersion. The resulting dispersion is then coated onto a
first barrier film, which is then dried. A second barrier film is
then heat laminated over the dispersion coated surface of the first
barrier film. Suitable first and last films and 3-D structures are
then heat laminated over the first and second barrier films and 3-D
structures.
[0365] In some embodiments, and referring to first layer 12 and
last layer 16 in FIG. 7 and first layer 52 and last layer 56 in
FIG. 9, the layers can be any suitable material independently
selected from polyethylene, polycarbonate, polypropylene, modified
cellulosic resins, clear polyvinyl chloride, acrylic resins,
polysiloxanes, epoxy resins, Safire, quartz and glass.
[0366] In many embodiments of the films and 3-D structures and
multilayer films and 3-D structures containing capped or capped and
passivated 2-6-6 semiconductor nanocrystals as described above are
advantageous compared to films and 3-D structures using crosslinked
polymers as is often used in the art. The photostability of the
resins used in the films and 3-D structures as described
hereinabove provide quantum dots and films and 3-D structures
containing quantum dots with improved photolytic stability.
[0367] In many embodiments of the films and 3-D structures the
composite material is prepared by combining the nanocrystals with
the polymer during or after polymerization in a suitable solvent,
then removing the solvent to produce a material that consists of
95-100% solid material that is essentially solvent-free. This
composite can then be injection molded, extruded, compression
molded, transfer molded and pressed or formed using a process that
first melts the composite and converts the composite into the
desirable 3-D shape. These 3-D parts are then used in an
optoelectronic device.
[0368] The quantum dots described herein may be included in
solutions, inks, films, resin pellets, thermoplastic pellets.
[0369] Solutions containing the quantum dots described herein may
be prepared simply by leaving the QDs in solution without drying or
by placing purified QDs in a suitable solution for later use.
[0370] As described above, the QDs can be embedded in a polymer
matrix to form films or 3-D structures. The composite (QD-matrix)
can also be pelletized for later use as resin pellets or
thermoplastic pellets which may then be used in subsequent molding
processes, much as traditional resin or polymer pellets are
used.
[0371] The QDs may be incorporated into an ink such as those
suitable for ink jet printing, 3-D printing, or other printing
techniques. The inks are generally prepared from the quantum dots
as described herein mixed with polymer, such as the acrylate
polymer described herein, and a solvent. Any suitable solvent, such
as, but not limited to, toluene, may be used. Other additives
useful in inks may also be employed, such as, but not limited to
flow agents, self-leveling agents, viscosity modifiers, de-bubbling
agents, binders, surfactants, etc. In some embodiments, the polymer
and solvent components account for about 1 to about 80% of the ink
composition. The quantum dots are present from about 0.1 mg to
about 100 mg of quantum dots per gram of polymer.
[0372] The present invention will further be described by reference
to the following examples. The following examples are merely
illustrative and are not intended to be limiting.
[0373] Unless otherwise indicated, all percentages are by weight
unless otherwise specified.
EXAMPLES
Example A1--530 nm Cd-Free Quantum Dots
[0374] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.01 g of
copper acetate along with 5 ml of octadecane, 0.5 ml of octanoic
acid, and 2 ml of 1-dodecanthiol were loaded into a three-neck
flask. Without degassing, the temperature was increased to
270.degree. C. The heat was removed after 10 minutes. The reaction
provided Cd-free quantum dots with an emission wavelength of about
530 nm.
Example A2--750 nm Cd-Free Quantum Dots
[0375] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.05 g of
copper acetate along with 5 ml of octadecane, 0.5 ml of Oleic acid,
and 2 ml of 1-dodecanthiol were loaded into a three-neck flask.
Without degassing, the temperature was increased to 270.degree. C.
The heat was removed after 10 minutes.
[0376] The reaction provided Cd-free ZnInCuS quantum dots with an
emission wavelength of about 750 nm.
Examples A3-A7: Cd-Free N Quantum Dots with Emission Wavelengths
Between 530 and 750 nm
[0377] By changing the Zn/Cu ratio, the emission wavelength of the
Cd-free quantum dots can be tuned to between 530 and 750 nm.
[0378] In examples 3 to 7, the reactions were carried out as in
example 1, except the amount of Copper Acetate used was as
indicated in Table 1, which shows the resulting emission spectrum
for some of the wavelengths.
TABLE-US-00001 TABLE 1 Copper Emission Example Acetate(g)
Wavelength (nm) A3 0.015 540 A4 0.018 560 A5 0.025 600 A6 0.035 660
A7 0.045 720
[0379] FIG. 10 shows the emission spectrum for some of the
wavelengths.
Example A8 Capping with Method 1
[0380] In a glovebox, a solution was prepared for use in the
deposition of one or more layers of ZnS onto the Cd-free
nanocrystals of example 1. When no change in emission wavelength
was observed of the Cd-free nanocrystals, the solution was injected
slowly into the nanocrystal solution. This injection process lasted
approximately two minutes.
[0381] The resultant solution was added to a 50 ml conical
centrifuge tube and 5 ml hexanes and 15 ml of butanol were added.
After sonication for about 1 minute, 20 ml methanol was added. The
nanocrystals were centrifuged and the supernatant was discarded.
The nanocrystals were washed two more times with 10 ml of hexanes,
precipitated with 20 ml of methanol and re-centrifuged.
[0382] The purified nanocrystals were transferred to a three-neck
round bottom flask and hexanes were removed by vacuum.
Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were
added. The flask was vacuum purged for 10 minutes and heated to
100.degree. C. for 30 minutes and then to 200.degree. C. for 30
minutes. The capping material was prepared in a glovebox as
follows: 40 ul of dimethylzinc, 80 ul of hexamethyldisilathiane and
4 ml of trioctylphosphine were mixed in a glass vial and sealed
with a robber stopper. The capping solution was put in a syringe,
removed from the glovebox, and slowly injected into the core
solution over at least 10 minutes. The resulting solution was
stirred for 30 minutes at 200.degree. C., then removed from heat
and allowed to cool to room temperature.
[0383] This example provided capped Cd-free nanocrystals.
Example A9 Capping with Method 2
[0384] 0.25 g of purified Cd-free cores from example 1 were placed
in a three-neck flask with 1 g of Zinc Acetate, 0.032 g of S, 2 ml
of 1-dodecanethiol, 10 ml of ODE and 2 ml of Octanoic acid.
Degassing was conducted for 20 minutes, then the flask was filled
with nitrogen, and the temperature raised to 240.degree. C., and
the reaction was allowed to progress for about 60 minutes.
[0385] This example provided capped Cd-free nanocrystals.
Example A10 Al.sub.2O.sub.3 Capping
[0386] In a glovebox, a solution was prepared for use in the
deposition of one or more layers of ZnS onto the Cd-free
nanocrystals of example 1. When no change in emission wavelength
was observed of the Cd-free nanocrystals, the solution was injected
slowly into the nanocrystal solution. This injection process lasted
approximately two minutes.
[0387] The resultant solution was added to a 50 ml conical
centrifuge tube and 5 ml hexanes and 15 ml of butanol were added.
After sonication for about 1 minute, 20 ml methanol was added. The
nanocrystals were centrifuged and the supernatant was discarded.
The nanocrystals were washed two more times with 10 ml of hexanes,
precipitated with 20 ml of methanol and re-centrifuged. The
purified capped Cd-free nanocrystals were suspended in hexanes for
further capping.
[0388] The purified nanocrystals were transferred to a three-neck
round bottom flask and hexanes were removed by vacuum.
Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were
added. The flask was vacuum purged for 10 minutes and heated to
100.degree. C. for 30 minutes and then to 200.degree. C. for 30
minutes. The capping material was prepared in a glovebox as
follows: 40 ul of dimethylzinc, 80 ul of hexamethyldisilathiane and
4 ml of trioctylphosphine were mixed in a glass vial and sealed
with a robber stopper. The capping solution was put in a syringe,
removed from the glovebox, and slowly injected into the core
solution over at least 10 minutes. The resulting solution was
stirred for 30 minutes at 200.degree. C., then removed from heat
and allowed to cool to room temperature.
[0389] Several monolayers of aluminum were grown on the capped
Cd-free nanocrystals as follows. The aluminum capping materials
were prepared in a glovebox by mixing 10 ul of trimethylaluminum
and 1 ml of trioctylphosphine to form a capping solution and scaled
with robber stopper. The capping solution was put in a syringe,
removed from the glovebox, and slowly injected into the core/shell
nanocrystal solution over about 5 minutes at 200.degree. C. then
removed from the heat and allow to cool to 100.degree. C., at which
point the flask was opened to air, which allowed the aluminum outer
coating on the core/shell nanocrystals to slowly oxidize over 3
hours at 100.degree. C. Several monolayers of Al.sub.2O.sub.3 were
coated on the core/shell nanocrystals providing passivated
core/shell Cd-free nanocrystals.
Example A11--ZnCuGaS
[0390] 0.25 g of zinc acetate, 0.3 g of Gallium Acetate, 0.01 g of
copper acetate along with 5 ml of octadecane, 0.5 ml of Octanoic
acid, and 2 ml of 1-dodecanthiol were loaded into a three flask.
Without degassing, the temperature was increases to 270.degree. C.
The heat was removed after 10 minutes.
[0391] This example provided Cd-free quantum dots with emission
wavelength around 550 nm.
Example A12--ZnCuAlS
[0392] 0.25 g of zinc acetate, 0.3 g of Aluminum Acetate, 0.01 g of
copper acetate along with 5 ml of octadecane, 0.5 ml of Octanoic
acid, and 2 ml of 1-dodecanthiol were loaded into a three flask.
Without degassing, the temperature was increased to 270.degree. C.
The heat was removed after 10 minutes.
[0393] This example provided Cd-free quantum dots with emission
wavelength around 490 nm.
Example A13 ZnCuInSSe
[0394] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.01 g of
copper acetate along with 5 ml of octadecane, 0.5 ml of Octanoic
acid, 200 ul of TBP/Se solution (concentration was 1 g/10 ml) and 2
ml of 1-dodecanthiol were loaded into a three flask. Without
degassing, the temperature was increased to 270.degree. C. The heat
was removed after 10 minutes.
[0395] This example provided Cd-free quantum dots with emission
wavelength around 550 nm.
Example A14--ZnCuInGaS
[0396] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.1 g of
Gallium Acetate, 0.01 g of copper acetate along with 5 ml of
octadecane, 0.5 ml of Octanoic acid, and 2 ml of 1-dodecanthiol
were loaded into a three flask. Without degassing, the temperature
was increased to 270.degree. C. The heat was removed after 10
minutes.
[0397] This example provided Cd-free quantum dots with emission
wavelength around 560 nm.
[0398] Example A15--ZnCuInGaSSe
[0399] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.1 g of
Gallium Acetate, 0.01 g of copper acetate along with 5 ml of
octadecane, 0.5 ml of Octanoic acid, 200 ul of TBP/Se solution
(concentration was 1 g/10 ml) and 2 ml of I-dodecanthiol were
loaded into a three flask. Without degassing, the temperature was
increased to 270.degree. C. The heat was removed after 10
minutes.
[0400] This example provided Cd-free quantum dots with emission
wavelength around 560 nm.
Example A16--ZnCuInAlS
[0401] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.1 g of
Aluminum Acetate, 0.01 g of copper acetate along with 5 ml of
octadecane, 0.5 ml of Octanoic acid, and 2 ml of 1-dodecanthiol
were loaded into a three flask. Without degassing, the temperature
was increased to 270.degree. C. The heat was removed after 10
minutes.
[0402] This example provided quantum dots with emission wavelength
around 500 nm.
Example A17--ZnCuInAlSSe
[0403] 0.25 g of zinc acetate, 0.3 g of Indium Acetate, 0.1 g of
Aluminum Acetate, 0.01 g of copper acetate along with 5 ml of
octadecane, 0.5 ml of Octanoic acid, 200 ul of TBP/Se solution
(concentration was 1 g/10 ml) and 2 ml of 1-dodecanthiol were
loaded into a three flask. Without degassing, the temperature was
increased to 270.degree. C. The heat was removed after 10
minutes.
[0404] This example provided quantum dots with emission wavelength
around 540 nm.
Example A18--ZnCuGaAlS
[0405] 0.25 g of zinc acetate, 0.3 g of Gallium Acetate, 0.1 g of
Aluminum Acetate, 0.01 g of copper acetate along with 5 ml of
octadecane, 0.5 ml of Octanoic acid, and 2 ml of 1-dodecanthiol
were loaded into a three flask. Without degassing, the temperature
was increased to 270.degree. C. The heat was removed after 10
minutes.
[0406] This example provided quantum dots with emission wavelength
around 500 nm.
Example A19--ZnCuGaAlSSe
[0407] 0.25 g of zinc acetate, 0.3 g of Gallium Acetate, 0.1 g of
Aluminum Acetate, 0.01 g of copper acetate along with 5 ml of
octadecane, 0.5 ml of Octanoic acid, 200 ul of TBP/Se solution
(concentration was 1 g/10 ml) and 2 ml of 1-dodecanthiol were
loaded into a three flask. Without degassing, the temperature was
increased to 270.degree. C. The heat was removed after 10
minutes.
[0408] This example provided quantum dots with emission wavelength
around 540 nm.
Example B1: pH Controller Tuned Qds
[0409] Core Synthesis
[0410] Zinc Acetate (0.2 g) (as pH controller), octadecene (80 mL)
was mixed with oleic acid (4 ml) and added to CdO (0.512 g) in a
three neck round bottom flask. The flask was flushed with 99.999%
nitrogen for 20 minutes and then heated to 300.degree. C. until the
solution was clear. Stock solutions of selenium and sulfur were
prepared in a glove box under 99.999% nitrogen. Selenium powder
(1.00 g) was mixed with tributylphosphine (10.00 mL) and sulfur
powder (0.050 g) was mixed with octadecene (20.00 mL). 200 .mu.L
selenium precursors were mixed with 20 mL sulfur precursors in a 20
mL glass vial, diluted to 2.00 mL with octadecene, and then added
to the cadmium precursors via a syringe and stirred for 60 minutes,
or until no change in emission wavelength is observed. This
produces cores that fluoresce at 570 nm.
Examples B2-B6
[0411] The same procedure for Example B1 was conducted for examples
B2-B6, except the amount of Zinc Acetate, as pH controller, in the
core synthesis was changed as indicated in the table below.
TABLE-US-00002 Zinc Emission Example Acetate(g) maximum (nm) B1
0.20 570 B2 0.25 590 B3 0.30 600 B4 0.40 640 B5 0.50 660 B6 0.70
680
[0412] This data can be graphed to provide a calibration curve to
determine the proper amount of Zinc Acetate for the desired
wavelength by plotting emission maximum on the Y-axis and Zinc
Acetate on the X-axis. A calibration curve based on this data is
shown in FIG. 12.
Examples B7-B11
[0413] The same procedure for Example B1 was conducted to produce
the cores for examples B7-B11. The cores were then subjected to
purification and capping.
[0414] Purification
[0415] The entire core solution was added to 80 mL of hexanes and
180 mL of butanol. The resultant solution was centrifuged (2,680 G
for 5 minutes) and the supernatant was discarded leaving
nanocrystals. The nanocrystals were washed three times by being
suspended in hexanes (10 mL), precipitated with methanol (30 mL)
and centrifuged (2,680 G for 10 minutes). The crystals were then
suspended in 5 mL hexanes.
[0416] Capping
[0417] The purified nanocrystals were transferred to a three neck
round bottom flask and the solvent (hexanes) removed by vacuum.
Zinc Acetate (see table below), octadecene (20 ml) and Oleic acid
(10 ml) were added to the flask. The flask was vacuum purged for 10
minutes and then heated to 100.degree. C. for 30 minutes and then
to 200.degree. C. for another 30 minutes. While the nanocrystals
were heating, the capping solution was prepared in a glove box as
follows:
[0418] Dimethyl zinc (40 .mu.L) was mixed with
hexamethyldisilathiane (80 .mu.L, CAS#3385-94-2) and
trioctylphosphine (2.00 mL). The capping solution was put in a
syringe, removed from the glovebox, and added to the nanocrystals
drop-by-drop over five minutes. The resulting solution was stirred
for two hours at 200.degree. C. and then allowed to cool to room
temperature.
[0419] The amount of Zinc Acetate (pH controller) was changed in
the capping step as indicated in the table below. The red shift
after capping indicates the longer the red shift, the thicker the
shell. A thicker shell nanocrystal can increase the photo and
chemical stability.
TABLE-US-00003 Zinc Emission maximum Example Acetate(g) red shift
(nm) B7 0.00 4 B8 0.10 6 B9 0.20 8 B10 0.40 10 B11 0.70 11
[0420] A calibration curve for the shift in emission wavelength
based on this data is shown in FIG. 13.
Example B12 (Comparative)
[0421] CdZnSSe nanocrystals were fabricated as follows. To a 100 ml
three-neck round bottom flask, 0.16 mmol of CdO, 0.4 mmol of
Zn(AC)2, 200 .mu.l of oleic acid and 8 ml of octadecene were added.
The flask was connected to a vacuum and degassed for about 10
minutes, then filled with high purity nitrogen, heated up to
300.degree. C., and stirred until a colorless solution was formed.
Stock solution of sulfur and selenium were prepared in a glovebox
filled with 99.999% nitrogen. Selenium powder (1.00 g) was mixed
with tributylphosphine (10.00 ml) and sulfur powder (0.05 g) was
mixed with octadecene (25.00 ml). An amount of the above sulfur and
selenium stock solutions were mixed together in a glass vial and
diluted with octadecene up to 4 ml resulting in a solution herein
called an injection solution. The amount of sulfur and selenium was
1 mmol in total, the S to Se ratio was determined by the final
emission wavelength of the derived nanocrystals. The injection
solution was removed from the glovebox using a syringe and injected
into the Cd and Zn precursor solution quickly while the growth
temperature was raised to 270.degree. C. This temperature was
maintained for 40 to 60 minutes to allow the nanocrystals to grow
to the desired size as determined by the desired emission
wavelength.
[0422] In the glovebox, a solution was prepared for use in the
deposition of one or more layers of ZnS onto the prepared
nanocrystals. When no change in emission wavelength was observed of
the above-prepared nanocrystals, the solution was injected slowly
into the nanocrystal solution. This injection process lasted
approximately two minutes.
[0423] The resultant solution was added to a 50 ml conical
centrifuge tube and 5 ml hexanes and 15 ml of butanol were added.
After sonication for about 1 minute, 20 ml methanol was added. The
nanocrystals were centrifuged and the supernatant was discarded.
The nanocrystals were washed two more times with 10 ml of hexanes,
precipitated with 20 ml of methanol and re-centrifuged. The
purified nanocrystals were suspended in hexanes for further
capping.
[0424] The purified nanocrystals were transferred to a three-neck
round bottom flask and hexanes were removed by vacuum.
Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were
added. The flask was vacuum purged for 10 minutes and heated to
100.degree. C. for 30 minutes and then to 200.degree. C. for 30
minutes. Capping material was prepared in a glovebox as follows: 40
ul of dimethylzinc, 80 ul of hexamethyldisilathiane and 4 ml of
trioctylphosphine were mixed in a glass vial and sealed with a
robber stopper. The capping solution was put in a syringe, removed
from the glovebox, and slowly injected into the core solution over
at least 10 minutes. The resulting solution was stirred for 30
minutes at 200.degree. C., then removed from heat and allowed to
cool to room temperature.
Examples B13 and B14
[0425] To compare the photo stability of the nanocrystals made in
this invention, a nanocrystal-polymethylmethacrylate (PMMA) film
was deposited and illuminated by an ultra-intense blue (450 nm) LED
to monitor the intensity decay. Films were prepared by dispersing
the nanocrystals in a toluene solution of PMMA using a Brinkman
Homogenizer and then coating films using an Elcometer 4340
Automatic Film Applicator and allowing the films to dry at room
temperature. In this way, the nanocrystals (5 mg), from example B11
and example B12, were added to PMMA (5 g) to make a thin film.
Under ultra-intense blue (450 nm) LED for continuous illumination.
FIG. 11 shows the stability testing result (Example B13 contains
the nanocrystals from example B11 and Example B14 contains the
nanocrystals from Example B12. The data demonstrate the
photostability of the nanocrystals made according to the
invention.
[0426] As can be seen, the film using nanocrystals according to
Example B11 in a PMMA film maintains emission for at least 120
minutes while the comparative nanocrystals of Example B12 in a PMMA
film drop significantly, even after only 20 minutes.
Examples B15-B20
[0427] Polymers were synthesis via free radical polymerization in
toluene. Vinyl-based monomers (as indicated in the table below,
where weight ratios of comonomers are indicated) with varied
amounts were used in the polymerization. Monomer(s) was (were)
dissolved in toluene (1 mL to 1 g of monomers). The initiator,
azobisisobutyronitrile (AIBN, 0.5 wt % to monomers), was added. The
mixture was purged with N2 for 30 min. The mixture was then heated
to 70.degree. C. and stirred overnight. The resulting product was
colorless viscous liquid. MMA=methyl methacrylate, BA=butyl
acrylate, CHA=cyclohexyl acrylate, NNDMT=Formula V where R3 and R4
are both methyl. Mw and PDI values were determined by GPC using
analytical standards.
TABLE-US-00004 Ex. M.sub.w T.sub.g Toluene No. Monomer(s) (Kg/mol)
PDI (.degree. C.) Solution B15 80/20 MMA/BA 51 1.7 65 transparent
B16 90/10 MMA/BA 50 1.7 93 transparent B17 95/5 MMA/BA 39 1.7 110
transparent B18 60/40 MMA/BA 108 2.3 Phase separated B19 100 CHA
100 transparent B20 100 NNDMT 19-30 transparent
[0428] Cast films were prepared by dispersing the nanocrystals of
Example B11 in a toluene solution of the polymers in Examples
B15-B20 using a Brinkman Homogenizer and then casting films using
an Elcometer 4340 Automatic Film Applicator and allowing the films
to dry at room temperature as was described in Examples B13 and
B14. All made acceptable films with improved stability as
demonstrated in Example B13, except for Example B18.
[0429] Extruded films were prepared by dispersing the nanocrystals
of Example B11 in a toluene solution of the polymers in Examples
B15-B20 using a Brinkman Homogenizer and then removing the toluene
in a vacuum oven at 125.degree. C. and 30 mm Hg vacuum. The
resulting material was then melted in a heated tube to 175.degree.
C. and extruded onto a glass slide and allowed to cool forming a
composite containing a concentration of 0.5 mg of nanocrystals per
1000 mg of polymer.
Example B21
[0430] Passivated CdZnSSe nanocrystals were fabricated as follows.
To a 100 ml three-neck round bottom flask, 0.16 mmol of CdO, 0.4
mmol of Zn(AC)2, 200 .mu.l of oleic acid and 8 ml of octadecene
were added. The flask was connected to a vacuum and degassed for
about 10 minutes, then filled with high purity nitrogen, heated up
to 300.degree. C., and stirred until a colorless solution was
formed. Stock solution of sulfur and selenium were prepared in a
glovebox filled with 99.999% nitrogen. Selenium powder (1.00 g) was
mixed with tributylphosphine (10.00 ml) and sulfur powder (0.05 g)
was mixed with octadecene (25.00 ml). An amount of the above sulfur
and selenium stock solutions were mixed together in a glass vial
and diluted with octadecene up to 4 ml resulting in a solution
herein called an injection solution. The amount of sulfur and
selenium was 1 mmol in total, the S to Se ratio was determined by
the final emission wavelength of the derived nanocrystals. The
injection solution was removed from the glovebox using a syringe
and injected into the Cd and Zn precursor solution quickly while
the growth temperature was raised to 270.degree. C. This
temperature was maintained for 40 to 60 minutes to allow the
nanocrystals to grow to the desired size as determined by the
desired emission wavelength.
[0431] In the glovebox, a solution was prepared for use in the
deposition of one or more layers of ZnS onto the prepared
nanocrystals. When no change in emission wavelength was observed of
the above-prepared nanocrystals, the solution was injected slowly
into the nanocrystal solution. This injection process lasted
approximately two minutes.
[0432] The resultant solution was added to a 50 ml conical
centrifuge tube and 5 ml hexanes and 15 ml of butanol were added.
After sonication for about 1 minute, 20 ml methanol was added. The
nanocrystals were centrifuged and the supernatant was discarded.
The nanocrystals were washed two more times with 10 ml of hexanes,
precipitated with 20 ml of methanol and re-centrifuged. The
purified nanocrystals were suspended in hexanes for further
capping.
[0433] The purified nanocrystals were transferred to a three-neck
round bottom flask and hexanes were removed by vacuum.
Trioctylphosphine oxide (8.0 g) and stearic acid (0.2 g) were
added. The flask was vacuum purged for 10 minutes and heated to
100.degree. C. for 30 minutes and then to 200.degree. C. for 30
minutes. Capping material was prepared in a glovebox as follows: 40
ul of dimethylzinc, 80 ul of hexamethyldisilathiane and 4 ml of
trioctylphosphine were mixed in a glass vial and sealed with a
robber stopper. The capping solution was put in a syringe, removed
from the glovebox, and slowly injected into the core solution over
at least 10 minutes. The resulting solution was stirred for 30
minutes at 200.degree. C., then removed from heat and allowed to
cool to room temperature.
[0434] Several monolayers of aluminum were grown on the
nanocrystals as follows. The aluminum capping materials were
prepared in a glovebox by mixing 10 ul of trimethylaluminum and 1
ml of trioctylphosphine to form a capping solution and sealed with
robber stopper. The capping solution was put in a syringe, removed
from the glovebox, and slowly injected into the core/shell
nanocrystal solution over about 5 minutes at 220.degree. C. then
removed from the heat and allow to cool to 100.degree. C., at which
point the flask was opened to air, which allowed the aluminum outer
coating on the core/shell nanocrystals to slowly oxidize over one
hour at 100.degree. C. Several monolayers of Al2O3 were coated on
the core/shell nanocrystals providing passivated core/shell
nanocrystals.
Example B22
[0435] A solution cast film containing the passivated nanocrystals
of Example B21 was prepared as follows: The passivated nanocrystals
of Example 16 were added to a 50/50 w/w solution of
cyclohexylacrylate homopolymer and toluene. The Mw of the polymer
was approximately 125,000. The passivated nanocrystals were added
at a concentration of 0.5 mg nanocrystals per gram of polymer. The
mixture was then mixed for 2 minutes with a high-shear mixer
(Brinkman, Model # PT/35). The mixture was them dried on a glass
slide to a thickness of 0.5 mm.
[0436] FIG. 14 shows an emission spectra of the solvent cast film
made using excitation at 450 nm and the emission in the red
wavelengths of the spectra.
Example B23
[0437] A melt extruded film containing the passivated nanocrystals
of Example B21 was prepared as follows: The passivated nanocrystals
of Example B21 were added to a 50/50 w/w solution of
cyclohexylacrylate homopolymer (Mw about 125,000) in toluene. The
mixture was then homogenized for 2 minutes with a high-shear mixer
(Brinkman, Model #PT/35). The homogenized mixture was dried to form
a nanocrystal/polymer composite material, which was ground into 1-5
mm chips and loaded into a glass syringe and heated to 175.degree.
C. The molten mixture was then extruded onto a glass slide at a
thickness of 0.5 mm.
[0438] FIG. 15 shows an emission spectra of the melt extruded film
made using excitation at 450 nm and the emission in the red
wavelengths of the spectra.
[0439] The present invention has been described with reference to
certain details of particular embodiments thereof. It is not
intended that such details be regarded as limitations upon the
scope of the invention except insofar as and to the extent that
they are included in the accompanying claims.
[0440] Thermoset Example:
[0441] An example of a thermoset acrylic formula that cures in the
presence of QDs is as follows: heptyl acrylate 60% (weight),
cyclohexyl acrylate 30%, trimethylolpropane triacrylate (TMPTA)
10%. To this is added a thermal initiator such as benzoyl peroxide
at 0.1% and QDs in the range of 0.001-20% wt/wt. The mixture is
polymerized by heating to 85 deg C. for 10 min.
[0442] It is contemplated herein that any quantum dot can be
subjected to the capping and passivation methods disclosed herein
and further incorporated into a polymer matrix as described herein.
The fact that the disclosure or examples above are directed to
specific combinations of particular quantum dot types, particular
capping, particular passivation layers, and a particular polymers
is not meant to suggest that this disclosure is limited to those
particular combinations. The disclosure is exemplary, and not
limiting, in nature. Those of skill in the art will recognize
variations of the theme without departing from the scope and spirit
of this disclosure.
* * * * *