U.S. patent application number 12/609736 was filed with the patent office on 2010-05-06 for light-emitting diode (led) devices comprising nanocrystals.
This patent application is currently assigned to NANOSYS, Inc.. Invention is credited to Jian Chen, Robert S. DUBROW, Veeral D. Hardev, Hans Jurgen Hofler, Ernest Lee.
Application Number | 20100110728 12/609736 |
Document ID | / |
Family ID | 42131162 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100110728 |
Kind Code |
A1 |
DUBROW; Robert S. ; et
al. |
May 6, 2010 |
LIGHT-EMITTING DIODE (LED) DEVICES COMPRISING NANOCRYSTALS
Abstract
The present invention provides light-emitting diode (LED)
devices comprises compositions and containers of hermetically
sealed luminescent nanocrystals. The present invention also
provides displays comprising the LED devices. Suitably, the LED
devices are white light LED devices.
Inventors: |
DUBROW; Robert S.; (San
Carlos, CA) ; Chen; Jian; (Sunnyvale, CA) ;
Hardev; Veeral D.; (Redwood City, CA) ; Hofler; Hans
Jurgen; (Sunnyvale, CA) ; Lee; Ernest; (Palo
Alto, CA) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX P.L.L.C.
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
NANOSYS, Inc.
Palo Alto
CA
|
Family ID: |
42131162 |
Appl. No.: |
12/609736 |
Filed: |
October 30, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12076530 |
Mar 19, 2008 |
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12609736 |
|
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60895656 |
Mar 19, 2007 |
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60985014 |
Nov 2, 2007 |
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Current U.S.
Class: |
362/615 ;
252/301.36; 313/512; 362/296.01; 428/690 |
Current CPC
Class: |
H01L 33/505 20130101;
Y02B 20/181 20130101; B82Y 20/00 20130101; H01L 2933/0041 20130101;
G02B 1/02 20130101; H01L 33/502 20130101; G02B 6/0041 20130101;
B32B 2457/206 20130101; H05B 33/04 20130101; Y10S 977/952 20130101;
C09K 11/025 20130101; Y10T 156/10 20150115; Y10S 977/834 20130101;
C09K 11/565 20130101; H01L 33/507 20130101; G02B 6/0068 20130101;
H01L 2924/0002 20130101; C09K 11/883 20130101; Y02B 20/00 20130101;
Y10S 977/81 20130101; G02B 1/10 20130101; H01L 2924/0002 20130101;
H01L 2924/00 20130101 |
Class at
Publication: |
362/615 ;
313/512; 362/296.01; 428/690; 252/301.36 |
International
Class: |
F21V 8/00 20060101
F21V008/00; H01J 1/62 20060101 H01J001/62; B44F 1/08 20060101
B44F001/08; C09K 11/02 20060101 C09K011/02 |
Claims
1. A light-emitting diode (LED) device, comprising: (a) a
blue-light emitting LED; and (b) a hermetically sealed container
comprising a plurality of luminescent nanocrystals, wherein the
container is placed with respect to the LED to facilitate
down-conversion of the luminescent nanocrystals.
2. The LED device of claim 1, wherein the hermetically sealed
container is a plastic or glass tube.
3. The LED device of claim 1, wherein the hermetically sealed
container is a glass capillary.
4. The LED device of claim 1, wherein the hermetically sealed
container is spaced apart from the LED.
5. The LED device of claim 1, wherein the luminescent nanocrystals
emit green light and red light.
6. The LED device of claim 1, wherein the luminescent nanocrystals
comprise CdSe or ZnS.
7. The LED device of claim 1, wherein the luminescent nanocrystals
are core/shell luminescent nanocrystals comprising CdSe/ZnS,
InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.
8. The LED device of claim 1, wherein the luminescent nanocrystals
are dispersed in a polymeric matrix.
9. A display system, comprising: (a) a display; and (b) a plurality
of light-emitting diode (LED) devices, the LED devices comprising:
(i) a blue light emitting LED; and (ii) a hermetically sealed
container comprising a plurality of luminescent nanocrystals,
wherein the container is placed with respect to the LED to
facilitate down-conversion of the luminescent nanocrystals.
10. The display system of claim 9, wherein the hermetically sealed
container is a plastic or glass tube.
11. The display system of claim 9, wherein the hermetically sealed
container is a glass capillary.
12. The display system of claim 9, wherein the hermetically sealed
container is spaced apart from the LED.
13. The display system of claim 9, wherein the luminescent
nanocrystals emit green light and red light.
14. The display system of claim 9, wherein the luminescent
nanocrystals comprise CdSe or ZnS.
15. The display system of claim 9, wherein the luminescent
nanocrystals are core/shell luminescent nanocrystals comprising
CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.
16. The display system of claim 9, wherein the luminescent
nanocrystals are dispersed in a polymeric matrix.
17. A light-emitting diode (LED) device, comprising: (a) an LED;
(b) a hermetically sealed container comprising a plurality of
luminescent nanocrystals optically coupled to the LED; and (c) a
light guide optically coupled to the hermetically sealed container,
wherein a first portion of light emitted from the LED is
down-converted by the luminescent nanocrystals, and wherein a
second portion of light emitted from the LED and the down-converted
light from the luminescent nanocrystals are emitted from the light
guide.
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. (canceled)
26. (canceled)
27. (canceled)
28. (canceled)
29. A white light light-emitting diode (LED) device, comprising:
(a) a blue light light-emitting LED; (b) a hermetically sealed
container comprising a plurality of CdSe/ZnS luminescent
nanocrystals optically coupled to the LED; and (c) a light guide
optically coupled the hermetically sealed container, wherein a
first portion of blue light emitted from the LED is down-converted
by the CdSe/ZnS luminescent nanocrystals to green light and red
light, and wherein a second portion of blue light emitted from the
LED, the green light and the red light, are emitted from the light
guide and combine to produce white light.
30. (canceled)
31. (canceled)
32. (canceled)
33. (canceled)
34. (canceled)
35. (canceled)
36. A display system, comprising: (a) a display; (b) a plurality of
light-emitting diode (LED) devices, the LED devices comprising: (i)
an LED; and (ii) a hermetically sealed container comprising a
plurality of luminescent nanocrystals optically coupled to the LED;
and (c) a light guide optically coupled to the hermetically sealed
container, wherein the display at least partially encloses the
light guide, wherein a first portion of light emitted from the LED
is down-converted by the luminescent nanocrystals, and wherein a
second portion of light emitted from the LED and the down-converted
light from the luminescent nanocrystals are emitted from the light
guide and displayed on the display.
37. (canceled)
38. (canceled)
39. (canceled)
40. (canceled)
41. (canceled)
42. (canceled)
43. (canceled)
44. (canceled)
45. (canceled)
46. (canceled)
47. (canceled)
48. A composite material, comprising: (a) a first polymeric
material having a first composition; (b) a second polymeric
material having a second composition; and (c) a plurality of
luminescent nanocrystals dispersed in the second polymeric
material, wherein the second polymeric material is dispersed in the
first polymeric material.
49. The composite material of claim 48, wherein the first polymeric
material comprises an epoxy or a polycarbonate.
50. The composite material of claim 48, wherein the second
polymeric material comprises aminosilicone.
51. The composite material of claim 48, wherein the luminescent
nanocrystals emit green light and/or red light.
52. The composite material of claim 48, wherein the luminescent
nanocrystals comprise CdSe or ZnS.
53. The composite material of claim 48, wherein the luminescent
nanocrystals are core/shell luminescent nanocrystals comprising
CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.
54. The composite material of claim 48, further comprising an
inorganic layer of SiO.sub.2, TiO.sub.2 or AlO.sub.2 hermetically
sealing the composite.
55. The composite material of claim 48, wherein the composite has
an optical density of about 0.5 to about 0.9 and a path length of
about 50 .mu.m to about 200 .mu.m.
56. The composite material of claim 55, wherein the composite has
an optical density of about 0.8 and a path length of about 100
.mu.m.
57. A method of preparing a luminescent nanocrystal composite
material, comprising: (a) dispersing a plurality of luminescent
nanocrystals in a first polymeric material to form a mixture of the
luminescent nanocrystals and the first polymeric material; (b)
curing the mixture; (c) generating a particulate from the cured
mixture; and (d) dispersing the particulate in a second polymeric
material to generate the composite material.
58. The method of claim 57, wherein the dispersing in (a) comprises
dispersing the luminescent nanocrystals in aminosilicone.
59. The method of claim 57, wherein the dispersing in (a) comprises
dispersing luminescent nanocrystals comprising CdSe or ZnS.
60. The method of claim 57, wherein the dispersing in (a) comprises
dispersing luminescent nanocrystals comprising CdSe/ZnS, InP/ZnS,
PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.
61. The method of claim 57, comprising adding a cross-linker to the
mixture prior to the curing in (b).
62. The method of claim 57, wherein the generating a particulate
comprises ball milling the cured mixture.
63. The method of claim 57, further comprising forming the
composite material into a film.
64. A light-emitting diode (LED) device, comprising: (a) an LED;
(b) a hermetically sealed container comprising a plurality of
luminescent nanocrystals optically coupled to the LED; and (c) a
light guide optically coupled to the hermetically sealed container,
wherein light emitted from the LED is down-converted by the
nanocrystals, and exits a surface of the light guide.
65. (canceled)
66. (canceled)
67. (canceled)
68. The LED device of claim 64, wherein the hermetically sealed
container is a glass capillary.
69. The LED device of claim 68, wherein the glass capillary has at
least one dimension of about 100 .mu.m to about 1 mm.
70. (canceled)
71. (canceled)
72. (canceled)
73. (canceled)
74. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of U.S.
application Ser. No. 12/076,530, filed Mar. 19, 2008. U.S.
application Ser. No. 12/076,530 claims the benefit of U.S.
Provisional Patent Application No. 60/895,656, filed Mar. 19, 2007,
and U.S. Provisional Patent Application No. 60/985,014, filed Nov.
2, 2007. The disclosures of each of these applications are
incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to methods light-emitting
diode (LED) devices comprising luminescent nanocrystals, suitably
white light LEDs. The present invention also relates to display
systems comprising the LED devices.
[0004] 2. Background of the Invention
[0005] Luminescent nanocrystals when exposed to air and moisture
undergo oxidative damage, often resulting in a loss of
luminescence. The use of luminescent nanocrystals in applications
such as down-conversion and filtering layers often expose
luminescent nanocrystals to elevated temperatures, high intensity
light, environmental gasses and moisture. These factors, along with
requirements for long luminescent lifetime in these applications,
often limits the use of luminescent nanocrystals or requires
frequent replacement. There exists a need therefore for methods and
compositions to hermetically seal luminescent nanocrystals, thereby
allowing for increased usage lifetime and luminescent
intensity.
[0006] There also exists a need for light-emitting diode (LED)
devices utilizing hermetically sealed nanocrystals, including white
light LED devices.
BRIEF SUMMARY OF THE INVENTION
[0007] In one embodiment, the present invention provides
light-emitting diode (LED) devices. The LED devices suitably
comprise a blue-light emitting LED and a hermetically sealed
container comprising a plurality of luminescent nanocrystals. The
container is placed with respect to the LED to facilitate
down-conversion of the luminescent nanocrystals.
[0008] Suitable hermetically sealed containers include plastic or
glass tubes, such as glass capillaries. In exemplary embodiments,
hermetically sealed container is spaced apart from the LED.
Suitably, the luminescent nanocrystals emit green light and red
light. Exemplary the luminescent nanocrystals for use in the LED
devices comprise CdSe or ZnS, including luminescent nanocrystals
that are core/shell luminescent nanocrystals comprising CdSe/ZnS,
InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS. In exemplary
embodiments, the luminescent nanocrystals are dispersed in a
polymeric matrix. The present invention also provides display
systems comprising the LED devices.
[0009] In further embodiments, the present invention provides
light-emitting diode (LED) devices comprising an LED, a
hermetically sealed container comprising a plurality of luminescent
nanocrystals optically coupled to the LED and a light guide
optically coupled to the hermetically sealed container. Suitably, a
first portion of light emitted from the LED is down-converted by
the luminescent nanocrystals, and a second portion of light emitted
from the LED, and the down-converted light from the luminescent
nanocrystals, are emitted from the light guide.
[0010] In exemplary embodiments, the LED emits blue light.
Suitably, the first portion of blue light emitted from the LED is
down-converted by the luminescent nanocrystals to green light and
red light. The second portion of blue light, the green light and
the red light suitably combine to produce white light.
[0011] Exemplary hermetically sealed containers include plastic or
glass containers, such as glass capillaries having least one
dimension of about 100 .mu.m to about 1 mm. Suitably, the
luminescent nanocrystals comprise CdSe or ZnS, and can be
core/shell nanocrystals comprising CdSe/ZnS, InP/ZnS, PbSe/PbS,
CdSe/CdS, CdTe/CdS or CdTe/ZnS. The luminescent nanocrystals can be
dispersed in a polymeric matrix. In suitable embodiments, the
hermetically sealed container is spaced apart from the LED. In
embodiments, the LED devices of the present invention are white
light LED devices.
[0012] The present invention also provides display systems
comprising a display and a plurality of the LED devices described
herein. Suitably, the display at least partially encloses the light
guide. A first portion of light emitted from the LED is
down-converted by the luminescent nanocrystals, and a second
portion of light emitted from the LED and the down-converted light
from the luminescent nanocrystals are emitted from the light guide
and displayed on the display. In exemplary embodiments, the
hermetically sealed container is optically coupled to at least two
LEDs.
[0013] In a still further embodiment, the present invention
provides composite materials. The composite materials comprise a
first polymeric material having a first composition. The composites
also comprise a second polymeric material having a second
composition, and a plurality of luminescent nanocrystals dispersed
in the second polymeric material. The second polymeric material is
dispersed in the first polymeric material.
[0014] Suitably, the first polymeric material comprises an epoxy or
a polycarbonate, and the second polymeric material comprises
aminosilicone. In embodiments, the luminescent nanocrystals emit
green light and/or red light. Suitably, the luminescent
nanocrystals comprise CdSe or ZnS, or can be core/shell luminescent
nanocrystals comprising CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS,
CdTe/CdS or CdTe/ZnS. In further embodiments, the composites
comprising an inorganic layer of SiO.sub.2, TiO.sub.2 or AlO.sub.2,
hermetically sealing the composite. Suitably, the composites have
an optical density of about 0.5 to about 0.9 (e.g., about 0.8) at
the blue LED wavelength and a path length of about 50 .mu.m to
about 200 .mu.m (e.g., about 100 .mu.m).
[0015] The present invention also provides methods of preparing
luminescent nanocrystal composite materials. The methods suitably
comprise dispersing a plurality of luminescent nanocrystals in a
first polymeric material to form a mixture of the luminescent
nanocrystals and the first polymeric material. The mixture is
cured, and a particulate is generated from the cured mixture. The
particulate is dispersed in a second polymeric material to generate
the composite material. Suitably, a cross-linker is added to the
mixture prior to the curing. In exemplary embodiments, the
particulate is generated by ball milling the cured mixture. The
composites can be formed into a film.
[0016] Additional features and advantages of the invention will be
set forth in the description that follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The advantages of the invention will be realized and
attained by the structure and particularly pointed out in the
written description and claims hereof as well as the appended
drawings.
[0017] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide further explanation of
the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0018] The accompanying drawings, which are incorporated herein and
form a part of the specification, illustrate the present invention
and, together with the description, further serve to explain the
principles of the invention and to enable a person skilled in the
pertinent art to make and use the invention.
[0019] FIG. 1 shows a hermetically sealed luminescent nanocrystal
composition in accordance with one embodiment of the present
invention.
[0020] FIG. 2 shows a method for hermetically sealing a container
comprising luminescent nanocrystals in accordance with one
embodiment of the present invention.
[0021] FIG. 3 shows hermetically sealed luminescent nanocrystal
compositions, including individually sealed compositions, in
accordance with one embodiment of the present invention.
[0022] FIG. 4 shows a hermetically sealed container comprising
luminescent nanocrystals in accordance with one embodiment of the
present invention.
[0023] FIG. 5 shows a hermetically sealed composition further
comprising a microlens in accordance with one embodiment of the
present invention.
[0024] FIGS. 6A-6C show a hermetically sealed composition further
comprising a light-focusing apparatus in accordance with one
embodiment of the present invention.
[0025] FIG. 7A shows an LED device in accordance with one
embodiment of the present invention.
[0026] FIG. 7B shows the down-conversion of light from an LED
device of the present invention.
[0027] FIGS. 8A-8C show variations of LED devices of the present
invention.
[0028] FIG. 9 shows an LED device of the present invention
comprising reflectors.
[0029] FIGS. 10A-10B show hermetically sealed capillaries in
accordance with embodiments of the present invention.
[0030] FIG. 11 shows a display device in accordance with an
embodiment of the present invention.
[0031] FIG. 12 shows a luminescent nanocrystal composite material
in accordance with an embodiment of the present invention.
[0032] FIG. 13 shows a flowchart of a method of preparing a
luminescent nanocrystal composite material in accordance with an
embodiment of the present invention.
[0033] FIG. 14 shows an LED device comprising a light guide with a
region of nanocrystals in accordance with an embodiment of the
present invention.
[0034] FIGS. 15A-15C show light intensity output for an LED device
comprising a light guide with a region of nanocrystals.
[0035] FIGS. 16A-16C show light intensity output for an LED device
comprising a light guide with a region of nanocrystals of
increasing thickness.
[0036] The present invention will now be described with reference
to the accompanying drawings. In the drawings, like reference
numbers indicate identical or functionally similar elements.
DETAILED DESCRIPTION OF THE INVENTION
[0037] It should be appreciated that the particular implementations
shown and described herein are examples of the invention and are
not intended to otherwise limit the scope of the present invention
in any way. Indeed, for the sake of brevity, conventional
electronics, manufacturing, semiconductor devices, and nanocrystal,
nanowire (NW), nanorod, nanotube, and nanoribbon technologies and
other functional aspects of the systems (and components of the
individual operating components of the systems) may not be
described in detail herein.
[0038] The present invention provides various compositions
comprising nanocrystals, including luminescent nanocrystals. The
various properties of the luminescent nanocrystals, including their
absorption properties, emission properties and refractive index
properties, can be tailored and adjusted for various applications.
As used herein, the term "nanocrystal" refers to nanostructures
that are substantially monocrystalline. A nanocrystal has at least
one region or characteristic dimension with a dimension of less
than about 500 nm, and down to on the order of less than about 1
nm. As used herein, when referring to any numerical value, "about"
means a value of +10% of the stated value (e.g. "about 100 nm"
encompasses a range of sizes from 90 nm to 110 nm, inclusive). The
terms "nanocrystal," "nanodot," "dot" and "quantum dot" are readily
understood by the ordinarily skilled artisan to represent like
structures and are used herein interchangeably. The present
invention also encompasses the use of polycrystalline or amorphous
nanocrystals. As used herein, the term "nanocrystal" also
encompasses "luminescent nanocrystals." As used herein, the term
"luminescent nanocrystals" means nanocrystals that emit light when
excited by an external energy source (suitably light). As used
herein when describing the hermetic sealing of nanocrystals, it
should be understood that in suitable embodiments, the nanocrystals
are luminescent nanocrystals.
[0039] Typically, the region of characteristic dimension will be
along the smallest axis of the structure. Nanocrystals can be
substantially homogenous in material properties, or in certain
embodiments, can be heterogeneous. The optical properties of
nanocrystals can be determined by their particle size, chemical or
surface composition. The ability to tailor the luminescent
nanocrystal size in the range between about 1 nm and about 15 nm
enables photoemission coverage in the entire optical spectrum to
offer great versatility in color rendering. Particle encapsulation
offers robustness against chemical and UV deteriorating agents.
[0040] Nanocrystals, including luminescent nanocrystals, for use in
the present invention can be produced using any method known to
those skilled in the art. Suitable methods and exemplary
nanocrystals are disclosed in U.S. patent application Ser. No.
11/034,216, filed Jan. 13, 2005; U.S. patent application Ser. No.
10/796,832, filed Mar. 10, 2004; U.S. Pat. No. 6,949,206; and U.S.
Provisional Patent Application No. 60/578,236, filed Jun. 8, 2004,
the disclosures of each of which are incorporated by reference
herein in their entireties. The nanocrystals for use in the present
invention can be produced from any suitable material, including an
inorganic material, and more suitably an inorganic conductive or
semiconductive material. Suitable semiconductor materials include
those disclosed in U.S. patent application Ser. No. 10/796,832, and
include any type of semiconductor, including group II-VI, group
III-V, group IV-VI and group IV semiconductors. Suitable
semiconductor materials include, but are not limited to, Si, Ge,
Sn, Se, Te, B, C (including diamond), P, BN, BP, BAs, AlN, AlP,
AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP,
AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe,
CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe,
SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI,
Si.sub.3N.sub.4, Ge.sub.3N.sub.4, Al.sub.2O.sub.3, (Al, Ga,
In).sub.2 (S, Se, Te).sub.3, Al.sub.2CO, and an appropriate
combination of two or more such semiconductors.
[0041] In certain aspects, the semiconductor nanocrystals may
comprise a dopant from the group consisting of: a p-type dopant or
an n-type dopant. The nanocrystals useful in the present invention
can also comprise II-VI or III-V semiconductors. Examples of II-VI
or III-V semiconductor nanocrystals include any combination of an
element from Group II, such as Zn, Cd and Hg, with any element from
Group VI, such as S, Se, Te, Po, of the Periodic Table; and any
combination of an element from Group III, such as B, Al, Ga, In,
and Tl, with any element from Group V, such as N, P, As, Sb and Bi,
of the Periodic Table.
[0042] The nanocrystals, including luminescent nanocrystals, useful
in the present invention can also further comprise ligands
conjugated, cooperated, associated or attached to their surface as
described throughout. Suitable ligands include any group known to
those skilled in the art, including those disclosed in U.S. patent
application Ser. No. 11/034,216, U.S. patent application Ser. No.
10/656,910 and U.S. Provisional Patent Application No. 60/578,236,
the disclosures of each of which are incorporated herein by
reference. Use of such ligands can enhance the ability of the
nanocrystals to incorporate into various solvents and matrixes,
including polymers. Increasing the miscibility (i.e., the ability
to be mixed without separation) of the nanocrystals in various
solvents and matrixes allows them to be distributed throughout a
polymeric composition such that the nanocrystals do not aggregate
together and therefore do not scatter light. Such ligands are
described as "miscibility-enhancing" ligands herein.
[0043] As used herein, the term nanocomposite refers to matrix
materials comprising nanocrystals distributed or embedded therein.
Suitable matrix materials can be any material known to the
ordinarily skilled artisan, including polymeric materials, organic
and inorganic oxides. Nanocomposites of the present invention can
be layers, encapsulants, coatings or films as described herein. It
should be understood that in embodiments of the present invention
where reference is made to a layer, polymeric layer, matrix, or
nanocomposite, these terms are used interchangeably, and the
embodiment so described is not limited to any one type of
nanocomposite, but encompasses any matrix material or layer
described herein or known in the art.
[0044] Down-converting nanocomposites (for example, as disclosed in
U.S. patent application Ser. No. 11/034,216) utilize the emission
properties of luminescent nanocrystals that are tailored to absorb
light of a particular wavelength and then emit at a second
wavelength, thereby providing enhanced performance and efficiency
of active sources (e.g., LEDs). As discussed above, use of
luminescent nanocrystals in such down-conversion applications, as
well as other filtering or coating applications, often exposes the
nanocrystals to elevated temperatures, high intensity light (e.g.,
an LED source), external gasses, and moisture. Exposure to these
conditions can reduce the efficiency of the nanocrystals, thereby
reducing useful product lifetime. In order to overcome this
problem, the present invention provides methods for hermetically
sealing luminescent nanocrystals, as well as hermetically sealed
containers and compositions comprising luminescent
nanocrystals.
Luminescent Nanocrystal Phosphors
[0045] While any method known to the ordinarily skilled artisan can
be used to create nanocrystal phosphors, suitably, a solution-phase
colloidal method for controlled growth of inorganic nanomaterial
phosphors is used. See Alivisatos, A. P., "Semiconductor clusters,
nanocrystals, and quantum dots," Science 271:933 (1996); X. Peng,
M. Schlamp, A. Kadavanich, A. P. Alivisatos, "Epitaxial growth of
highly luminescent CdSe/CdS Core/Shell nanocrystals with
photostability and electronic accessibility," J. Am. Chem. Soc.
30:7019-7029 (1997); and C. B. Murray, D. J. Norris, M. G. Bawendi,
"Synthesis and characterization of nearly monodisperse CdE
(E=sulfur, selenium, tellurium) semiconductor nanocrystallites," J.
Am. Chem. Soc. 115:8706 (1993), the disclosures of which are
incorporated by reference herein in their entireties. This
manufacturing process technology leverages low cost processability
without the need for clean rooms and expensive manufacturing
equipment. In these methods, metal precursors that undergo
pyrolysis at high temperature are rapidly injected into a hot
solution of organic surfactant molecules. These precursors break
apart at elevated temperatures and react to nucleate nanocrystals.
After this initial nucleation phase, a growth phase begins by the
addition of monomers to the growing crystal. The result is
freestanding crystalline nanoparticles in solution that have an
organic surfactant molecule coating their surface.
[0046] Utilizing this approach, synthesis occurs as an initial
nucleation event that takes place over seconds, followed by crystal
growth at elevated temperature for several minutes. Parameters such
as the temperature, types of surfactants present, precursor
materials, and ratios of surfactants to monomers can be modified so
as to change the nature and progress of the reaction. The
temperature controls the structural phase of the nucleation event,
rate of decomposition of precursors, and rate of growth. The
organic surfactant molecules mediate both solubility and control of
the nanocrystal shape. The ratio of surfactants to monomer,
surfactants to each other, monomers to each other, and the
individual concentrations of monomers strongly influence the
kinetics of growth.
[0047] In suitable embodiments, CdSe is used as the nanocrystal
material, in one example, for visible light down-conversion, due to
the relative maturity of the synthesis of this material. Due to the
use of a generic surface chemistry, it is also possible to
substitute non-cadmium-containing nanocrystals.
Core/Shell Luminescent Nanocrystals
[0048] In semiconductor nanocrystals, photo-induced emission arises
from the band edge states of the nanocrystal. The band-edge
emission from luminescent nanocrystals competes with radiative and
non-radiative decay channels originating from surface electronic
states. X. Peng, et al., J. Am. Chem. Soc. 30:7019-7029 (1997). As
a result, the presence of surface defects such as dangling bonds
provide non-radiative recombination centers and contribute to
lowered emission efficiency. An efficient and permanent method to
passivate and remove the surface trap states is to epitaxially grow
an inorganic shell material on the surface of the nanocrystal. X.
Peng, et al., J. Am. Chem. Soc. 30:7019-7029 (1997). The shell
material can be chosen such that the electronic levels are type I
with respect to the core material (e.g., with a larger bandgap to
provide a potential step localizing the electron and hole to the
core). As a result, the probability of non-radiative recombination
can be reduced.
[0049] Core-shell structures are obtained by adding organometallic
precursors containing the shell materials to a reaction mixture
containing the core nanocrystal. In this case, rather than a
nucleation-event followed by growth, the cores act as the nuclei,
and the shells grow from their surface. The temperature of the
reaction is kept low to favor the addition of shell material
monomers to the core surface, while preventing independent
nucleation of nanocrystals of the shell materials. Surfactants in
the reaction mixture are present to direct the controlled growth of
shell material and ensure solubility. A uniform and epitaxially
grown shell is obtained when there is a low lattice mismatch
between the two materials.
[0050] Exemplary materials for preparing core-shell luminescent
nanocrystals include, but are not limited to, Si, Ge, Sn, Se, Te,
B, C (including diamond), P, Co, Au, BN, BP, BAs, AlN, AlP, AlAs,
AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs,
AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe,
HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS,
SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI,
Si.sub.3N.sub.4, Ge.sub.3N.sub.4, Al.sub.2O.sub.3, (Al, Ga,
In).sub.2 (S, Se, Te).sub.3, Al.sub.2CO, and an appropriate
combination of two or more such materials. Exemplary core-shell
luminescent nanocrystals for use in the practice of the present
invention include, but are not limited to, (represented as
Core/Shell), CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS,
CdTe/ZnS, as well as others.
Hermetically Sealed Luminescent Nanocrystal Compositions and
Luminescent Nanocrystal-comprising Containers
[0051] In one embodiment, the present invention provides methods of
hermetically sealing a composition comprising a plurality of
luminescent nanocrystals. The methods suitably comprise disposing a
barrier layer on the composition to seal the luminescent
nanocrystals. As discussed throughout, the terms "hermetic,"
"hermetic sealing," and "hermetically sealed" are used throughout
to indicate that the composition, container and/or luminescent
nanocrystals are prepared in such a way that the quantity of gases
(e.g., air) or moisture that passes through or penetrates the
container or composition, and/or that contacts the luminescent
nanocrystals is reduced to a level where it does not substantially
effect the performance of the nanocrystals (e.g., their
luminescence). Therefore, a "hermetically sealed composition," for
example one that comprises luminescent nanocrystals, is a
composition that does not allow an amount of air (or other gas,
liquid or moisture) to penetrate the composition and contact the
luminescent nanocrystals such that the performance of the
nanocrystals (e.g., the luminescence) is substantially effected or
impacted (e.g., reduced).
[0052] As used throughout, a plurality of luminescent nanocrystals
means more than one nanocrystal (i.e., 2, 3, 4, 5, 10, 100, 1,000,
1,000,000, etc., nanocrystals). The compositions will suitably
comprise luminescent nanocrystals having the same composition,
though in further embodiments, the plurality of luminescent
nanocrystals can be various different compositions. For example,
the luminescent nanocrystals can all emit at the same wavelength,
or in further embodiments, the compositions can comprise
luminescent nanocrystals that emit at different wavelengths.
[0053] As shown in FIG. 1, in one embodiment, the present invention
provides a composition 100 comprising a plurality of luminescent
nanocrystals 104. Any nanocrystal can be prepared in the
compositions of the present invention, including those described
throughout, and otherwise known in the art, for example, as
disclosed in U.S. patent application Ser. No. 11/034,216.
[0054] In suitable embodiments, composition 100 comprises a
plurality of luminescent nanocrystals 104 dispersed throughout a
matrix 102. As used throughout, dispersed includes uniform (i.e.,
substantially homogeneous) as well as non-uniform (i.e.,
substantially heterogeneous) distribution/placement of
nanocrystals. Suitable matrixes for use in the compositions of the
present invention include polymers and organic and inorganic
oxides. Suitable polymers for use in the matrixes of the present
invention include any polymer known to the ordinarily skilled
artisan that can be used for such a purpose. In suitable
embodiments, the polymer will be substantially translucent or
substantially transparent. Such polymers include, but are not
limited to, poly(vinyl butyral):poly(vinyl acetate); epoxies;
urethanes; silicone and derivatives of silicone, including, but not
limited to, polyphenylmethylsiloxane, polyphenylalkylsiloxane,
polydiphenylsiloxane, polydialkylsiloxane, fluorinated silicones
and vinyl and hydride substituted silicones; acrylic polymers and
copolymers formed from monomers including but not limited to,
methylmethacrylate, butylmethacrylate and laurylmethacrylate;
styrene based polymers; and polymers that are crosslinked with
difunctional monomers, such as divinylbenzene.
[0055] The luminescent nanocrystals used the present invention can
be embedded in a polymeric (or other suitable material, e.g.,
waxes, oils) matrix using any suitable method, for example, mixing
the nanocrystals in a polymer and casting a film, mixing the
nanocrystals with monomers and polymerizing them together, mixing
the nanocrystals in a sol-gel to form an oxide, or any other method
known to those skilled in the art. As used herein, the term
"embedded" is used to indicate that the luminescent nanocrystals
are enclosed or encased within the polymer that makes up the
majority component of the matrix. It should be noted that
luminescent nanocrystals are suitably uniformly distributed
throughout the matrix, though in further embodiments they can be
distributed according to an application-specific uniformity
distribution function.
[0056] The thickness of the composition of the present invention
can be controlled by any method known in the art, such as spin
coating and screen printing. The luminescent nanocrystal
compositions of the present invention can be any desirable size,
shape, configuration and thickness. For example, the compositions
can be in the form of layers, as well as other shapes, for example,
discs, spheres, cubes or blocks, tubular configurations and the
like. While the various compositions of the present invention can
be any thickness required or desired, suitably, the compositions
are on the order of about 100 mm in thickness (i.e., in one
dimension), and down to on the order of less than about 1 mm in
thickness. In other embodiments, the polymeric layers of the
present invention can be on the order of 10's to 100's of microns
in thickness. The luminescent nanocrystals can be embedded in the
various compositions/matrixes at any loading ratio that is
appropriate for the desired function. Suitably, the luminescent
nanocrystals will be loaded at a ratio of between about 0.001% and
about 75% by volume depending upon the application, matrix and type
of nanocrystals used. The appropriate loading ratios can readily be
determined by the ordinarily skilled artisan and are described
herein further with regard to specific applications. In exemplary
embodiments the amount of nanocrystals loaded in a luminescent
nanocrystal composition are on the order of about 10% by volume, to
parts-per-million (ppm) levels.
[0057] Luminescent nanocrystals for use in the present invention
will suitably be less than about 100 nm in size, and down to less
than about 2 nm in size. In suitable embodiments, the luminescent
nanocrystals of the present invention absorb visible light. As used
herein, visible light is electromagnetic radiation with wavelengths
between about 380 and about 780 nanometers that is visible to the
human eye. Visible light can be separated into the various colors
of the spectrum, such as red, orange, yellow, green, blue, indigo
and violet. The photon-filtering nanocomposites of the present
invention can be constructed so as to absorb light that makes up
any one or more of these colors. For example, the nanocomposites of
the present invention can be constructed so as to absorb blue
light, red light, or green light, combinations of such colors, or
any colors in between. As used herein, blue light comprises light
between about 435 nm and about 500 nm, green light comprises light
between about 520 nm and 565 nm and red light comprises light
between about 625 nm and about 740 nm in wavelength. The ordinarily
skilled artisan will be able to construct nanocomposites that can
filter any combination of these wavelengths, or wavelengths between
these colors, and such nanocomposites are embodied by the present
invention.
[0058] In other embodiments, the luminescent nanocrystals have a
size and a composition such that they absorb photons that are in
the ultraviolet, near-infrared, and/or infrared spectra. As used
herein, the ultraviolet spectrum comprises light between about 100
nm to about 400 nm, the near-infrared spectrum comprises light
between about 750 nm to about 100 .mu.m in wavelength and the
infrared spectrum comprises light between about 750 nm to about 300
.mu.m in wavelength.
[0059] While luminescent nanocrystals of any suitable material can
be used in the practice of the present invention, in certain
embodiments, the nanocrystals can be ZnS, InAs or CdSe
nanocrystals, or the nanocrystals can comprise various combinations
to form a population of nanocrystals for use in the practice of the
present invention. As discussed above, in further embodiments, the
luminescent nanocrystals are core/shell nanocrystals, such as
CdSe/ZnS, CdSe/CdS or InP/ZnS.
[0060] In order to hermetically seal the compositions of the
present invention, a barrier layer is disposed on the composition.
For example, as shown in FIG. 1, a barrier layer 106 is disposed on
the matrix 102 comprising luminescent nanocrystals 104, thereby
generating a hermetically sealed composition. The term "barrier
layer" is used throughout to indicate a layer, coating, sealant or
other material that is disposed on the matrix 102 so as to
hermetically seal the composition. Examples of barrier layers
include any material layer, coating or substance that can create an
airtight seal on the composition. Suitable barrier layers include
inorganic layers, suitably an inorganic oxide such as an oxide of
Al, Ba, Ca, Mg, Ni, Si, Ti or Zr. Exemplary inorganic oxide layers,
include SiO.sub.2, TiO.sub.2, AlO.sub.2 and the like. As used
throughout, the terms "dispose," and "disposing" include any
suitably method of application of a barrier layer. For example,
disposing includes layering, coating, spraying, sputtering, plasma
enhanced chemical vapor deposition, atomic layer deposition, or
other suitable method of applying a barrier layer to the
compositions. In suitable embodiments, sputtering is used to
dispose the barrier layer on the compositions. Sputtering comprises
a physical vapor deposition process where high-energy ions are used
to bombard elemental sources of material, which eject vapors of
atoms that are then deposited in thin layers on a substrate. See
for example, U.S. Pat. Nos. 6,541,790; 6,107,105; and 5,667,650,
the disclosures of each of which are incorporated by reference
herein in their entireties.
[0061] In further embodiments, disposing the barrier layer can be
carried out using atomic layer deposition. In applications such as
coatings of LEDs, luminescent nanocrystal compositions, such as
nanocrystal-comprising polymeric layers, can often have complex
geometries and features. For example, components of the LED such as
bond wires and solder joints often are directly in contact with, or
even contained within, the polymeric layer. In order to properly
hermetically seal the nanocrystal composition, a virtually
defect-free (i.e., pin hole-free) barrier layer is often required.
In addition, application of the barrier layer should not degrade
the polymer or the nanocrystals. Therefore, in suitable
embodiments, atomic layer deposition is used to dispose the barrier
layer.
[0062] Atomic layer deposition (ALD) can comprise disposition of an
oxide layer (e.g., TiO.sub.2, SiO.sub.2, AlO.sub.2, etc.) on the
luminescent nanocrystal composition, or in further embodiments,
deposition of a non-conductive layer, such as a nitride (e.g.,
silicon nitride) can be used. ALD deposits an atomic layer (i.e.,
only a few molecules thick) by alternately supplying a reaction gas
and a purging gas. A thin coating having a high aspect ratio,
uniformity in a depression, and good electrical and physical
properties, can be formed. Barrier layers deposited by the ALD
method suitably have a low impurity density and a thickness of less
than 1000 nm, suitably less than about 500 nm, less than about 200
nm, less than about 50 nm, less than about 20 nm, or less than
about 5 nm.
[0063] For example, in suitable embodiments, two reaction gases, A
and B are used. When only the reaction gas, A, flows into a
reaction chamber, atoms of the reaction gas A are chemically
adsorbed on the luminescent nanocrystal composition. Then, any
remaining reaction gas A is purged with an inert gas such as Ar or
nitrogen. Then, reaction gas B flows in, wherein a chemical
reaction between the reaction gases A and B occurs only on the
surface of the luminescent nanocrystal composition on which the
reaction gas A has been adsorbed, resulting in an atomic barrier
layer on the composition.
[0064] In embodiments where a non-conductive layer, such as a
nitride layer is disposed, suitably SiH.sub.2Cl.sub.2 and remote
plasma enhanced NH.sub.3 are used to dispose a silicon nitride
layer. This can be performed at a low temperature and does not
require the use of reactive oxygen species.
[0065] Use of ALD for disposition of a barrier layer on the
luminescent nanocrystal composition generates a virtually pin-hole
free barrier layer regardless of the morphology of the substrate.
The thickness of the barrier layer can be increased by repeating
the deposition steps, thereby increasing the thickness of the layer
in atomic layer units according to the number of repetitions. In
addition, the barrier layer can be further coated with additional
layers (e.g., via sputtering, CVD or ALD) to protect or further
enhance the barrier.
[0066] Suitably, the ALD methods utilized in the practice of the
present invention are performed at a temperature of below about
500.degree. C., suitably below about 400.degree. C., below about
300.degree. C., or below about 200.degree. C.
[0067] Exemplary barrier materials include organic material
designed to specifically reduce oxygen and moisture transmission.
Examples include filled epoxies (such as alumina filled epoxies) as
well as liquid crystalline polymers.
[0068] As discussed throughout, matrix 102 suitably comprises a
polymeric substrate. Thus, the present invention comprises methods
of hermetically sealing compositions comprising luminescent
nanocrystals, suitably polymeric substrates comprising luminescent
nanocrystals, by disposing a barrier layer on the composition using
any of the various methods disclosed herein or otherwise known in
the art.
[0069] The ability to use polymeric substrates as matrix 102 allows
for the formation of various shapes and configurations of the
compositions, simply by molding or otherwise manipulating the
compositions into the desired shape/orientation. For example, a
solution/suspension of luminescent nanocrystals can be prepared
(e.g., luminescent nanocrystals in a polymeric matrix). This
solution can then be placed into any desired mold to form a
required shape, and then cured (e.g., cooled or heated depending
upon the type of polymer) to form a solid or semi-solid structure.
For example, a mold can be prepared in the shape of a cap or disc
to place on or over an LED. This then allows for preparation of a
composition that can be used as a down-converting layer, for
example. Following preparation of the desired shape, a barrier
layer is then disposed on the composition to hermetically seal the
composition, thereby protecting the luminescent nanocrystals from
oxidation.
[0070] In additional embodiments, a composition comprising
luminescent nanocrystals (e.g., a polymeric composition) can be
disposed directly on a desired substrate or article (for example an
LED). The luminescent nanocrystal composition (e.g., a solution or
suspension) can then be cured and then a barrier layer disposed on
the composition, thereby hermetically sealing the composition
directly on the desired substrate or article. Such embodiments
therefore do not require the preparation of a separate composition,
and instead allow for the preparation of the composition directly
on the desired article/substrate (e.g., a light source or other end
product).
[0071] In a further embodiment, the present invention provides
methods for hermetically sealing a container which comprises a
plurality of luminescent nanocrystals. Suitably the methods
comprise providing a container, introducing luminescent
nanocrystals into the container, and then sealing the container.
For example, an exemplary method for hermetically sealing a
container of luminescent nanocrystals is shown in flowchart 200 of
FIG. 2, with reference to FIGS. 3 and 4. In step 202 if FIG. 2, a
container is provided, for example, containers 302 or 402 in FIGS.
3 and 4 are be provided. As used herein, "container" refers to any
suitable article or receptacle for retaining nanocrystals. It
should be understood that, as used herein, a "container" comprising
luminescent nanocrystals and a "composition" comprising luminescent
nanocrystals represent different embodiments of the present
invention. A "composition" comprising luminescent nanocrystals
refers to a matrix, e.g., a polymer substrate, solution or
suspension, which contains nanocrystals dispersed throughout. A
"container" as used herein, refers to a carrier, receptacle or
pre-formed article into which luminescent nanocrystals are
introduced (often a composition of luminescent nanocrystals, e.g.,
a polymeric matrix comprising luminescent nanocrystals). Examples
of containers include, but are not limited to, polymeric or glass
structures such as tubes, molded or formed vessels, or receptacles.
In exemplary embodiments, a container can be formed by extruding a
polymeric or glass substance into a desired shape, such as a tube
(circular, rectangular, triangular, oval or other desired
cross-section), or similar structure. Any polymer can be used to
form the containers for use in the practice of the present
invention, including those described throughout. Exemplary polymers
for preparation of containers for use in the practice of the
present invention include, but are not limited to, acrylics,
poly(methyl methacrylate) (PMMA), and various silicone derivatives.
Additional materials can also be used to form the containers for
use in the practice of the present invention. For example, the
containers can be prepared from metals, various glasses, ceramics
and the like.
[0072] For example, as shown in FIG. 2, once a container is
provided in step 202, a plurality of luminescent nanocrystals 104
are then introduced into the container in step 204. As used herein,
"introduced" includes any suitable method of providing luminescent
nanocrystals into a container. For example, luminescent
nanocrystals can be injected into a container, placed into a
container, drawn into a container (e.g., by using a suction or
vacuum mechanism), directed into a container, for example by using
an electromagnetic field, or other suitable method for introducing
luminescent nanocrystals into a container. Suitably, the
luminescent nanocrystals are present in a solution or suspension,
for example in a polymeric solution, thereby aiding in the
introduction of the nanocrystals into the container. In exemplary
embodiments, luminescent nanocrystals 104 can be drawn into a
container, for example a tubular container 302, such as is shown in
FIG. 3. In further embodiments, as shown in FIG. 4, a container 402
can be prepared with a cavity or void 404 into which luminescent
nanocrystals 104 can be introduced. For example, a solution of
luminescent nanocrystals 104 can be introduced into the cavity 404
in container 402.
[0073] Following introduction of the luminescent nanocrystals into
the container, the container is then hermetically sealed, as shown
in FIG. 2, in step 206. Examples of methods for hermetically
sealing the container include, but are not limited to, heat sealing
the container, ultrasonic welding the container, soldering the
container or adhesive bonding the container. For example, as shown
in FIG. 3, container 302 can be sealed at any number of positions,
creating various number of seals 304 throughout the container. In
exemplary embodiments, container 302 can be heat sealed at various
positions throughout the container, for example by heating and then
"pinching" the container at various sealing points (304).
[0074] In suitable embodiments, as shown in FIG. 3, a polymeric or
glass tube can be used as container 302. A solution of luminescent
nanocrystals 104 can then be drawn into the container by simply
applying a reduced pressure to an end of the container. Container
302 can then be sealed by heating and "pinching" the container at
various sealing positions or seals 304 throughout the length of the
container, or by using other sealing mechanisms as described
throughout. In this way, container 302 can be separated into
various individual sections 306. These sections can either retained
together as a single, sealed container 308, or the sections can be
separated into individual pieces, as shown in FIG. 3. Hermetic
sealing of container 302 can be performed such that each individual
seal 304 separates solutions of the same nanocrystals. In other
embodiments, seals 304 can be created such that separate sections
of container 302 each contain a different nanocrystal solution
(i.e., different nanocrystal composition, size or density).
[0075] In a further embodiment, as shown in FIG. 4, luminescent
nanocrystals can be placed into a cavity/void 404 formed in
container 402. Container 402 can be produced using any suitable
process. For example, container 402 can be injection molded into
any desired shape or configuration. Cavity/void 404 can be prepared
during the initial preparation process (i.e., during molding) or
can be subsequently added after formation. Luminescent nanocrystals
104 are then introduced into cavity/void 404. For example,
luminescent nanocrystals can be injected or placed into cavity/void
404 of container 402. Suitably, a solution of luminescent
nanocrystals will fill the entire container, though it is not
necessary to completely fill the container with nanocrystals. In
the case where the entire container is not filled, it is necessary
though to remove substantially all of the air in the container
prior to sealing to ensure that the luminescent nanocrystals are
hermetically sealed. As shown in FIG. 4, in exemplary embodiments,
container 402 can be hermetically sealed by bonding, welding or
otherwise sealing the container with a cover or lid 406. Suitably,
cover 406 is produced from the same material as container 402 (and
can suitably be partially attached prior to sealing), though it can
also comprise a different material. In additional embodiments, a
material such as an organic material designed to specifically
reduce oxygen and moisture transmission can be used to cover or
seal container 402. Examples include filled epoxies (such as
alumina filled epoxies) as well as liquid crystalline polymers.
[0076] The ability to produce custom designed containers, for
example via molding, extruding or otherwise shaping containers,
allows for preparation of very specialized parts into which
luminescent nanocrystals can be introduced and hermetically sealed.
For example, shapes can be produced that conform around LEDs or
other light sources (e.g., for use to pipe down-conversion into
another optical component). In addition, various films, discs,
layers, and other shapes can be prepared. In exemplary embodiments,
several different containers can be prepared, each of which can
contain different compositions of luminescent nanocrystals (i.e.,
each composition emitting a different color), and then the separate
containers can be utilized together to create the desired
performance characteristics. In further embodiments, containers can
be prepared with multiple cavities or reservoirs into which
luminescent nanocrystals can be introduced.
[0077] While luminescent nanocrystals 104 can be hermetically
sealed into containers 302, 402, while still in solution, suitably
the luminescent nanocrystal solution is cured before hermetic
sealing (e.g., in step 210 of FIG. 2). As used herein, "cured"
refers to the process of hardening a solution of luminescent
nanocrystals (e.g., a polymeric solution). Curing can be achieved
by simply allowing the solution to dry and any solvent to
evaporate, or curing can be achieve by heating or exposing the
solution to light or other external energy. Following curing, the
container can be hermetically sealed using the various methods
described throughout.
[0078] In exemplary embodiments, no additional hermetic sealing is
necessary to protect the luminescent nanocrystals from oxidative
degradation. For example, sealing luminescent nanocrystals in a
glass or polymeric container provides sufficient protection from
oxygen and moisture that further modifications are not necessary.
However, in further embodiments, an additional level of protection
from oxidation can be added to the hermetically sealed containers
by disposing a barrier layer on the container. For example, as
shown in step 208 of FIG. 2. As described throughout, exemplary
barrier layers include inorganic layers, such as inorganic oxides
like SiO.sub.2, TiO.sub.2 and AlO.sub.2, as well as organic
materials. While any method of disposing the barrier layer onto the
container can be used, suitably the barrier layer is sputtered onto
the container or disposed onto the container via ALD. As shown in
FIG. 3, barrier layer 106 can be disposed on the container with
sealed sections, or on individual sections following sealing and
separation from one another, thereby producing hermetically sealed
containers (310, 312).
[0079] In suitable embodiments of the present invention, the
various steps to produce a hermetically sealed container of
luminescent nanocrystals are performed in an inert atmosphere. For
example, steps 204, 206 and 208 (and 210 if required) are all
suitably performed in an inert atmosphere, i.e., either in a vacuum
and/or with only N.sub.2 or other inert gas(es) present.
[0080] In further embodiments, the present invention provides
hermetically sealed compositions and containers comprising a
plurality of luminescent nanocrystals. In exemplary embodiments,
the luminescent nanocrystals comprise one or more semiconductor
materials (as described throughout), and are suitably core/shell
luminescent nanocrystals, such as CdSe/ZnS, CdSe/CdS or InP/ZnS. In
general, the luminescent nanocrystals are of a size of between
about 1-50 nm, suitably about 1-30 nm, more suitably about 1-10 nm,
e.g., about 3-9 nm. In exemplary embodiments, as described
throughout, the hermetically sealed compositions and containers of
the present invention comprise a barrier layer coating the
composition (e.g., barrier layer 106 coating composition 100 in
FIG. 1) and optionally comprise a barrier layer coating the
containers (e.g., barrier layer 106 coating container 302 in FIG.
3). Exemplary types of barrier layers include those described
throughout, such as inorganic layers like SiO.sub.2, TiO.sub.2, and
AlO.sub.2.
[0081] In addition to generating various shapes, orientations and
sizes of containers for hermetically sealing the luminescent
nanocrystals, additional modifications can also be made to the
containers/compositions. For example, the containers/compositions
can be prepared in the shape of a lens for filtration or other
modification of a light source. In further embodiments, the
containers/compositions can be modified, for example, by preparing
or attaching a reflector or similar apparatus to the
containers/compositions.
[0082] Additionally, micropatterns can be molded directly into the
compositions or containers to form flat (or curved) microlenses.
This can be done during the molding process or in a subsequent
embossing step. Micropatterns are often utilized to make flat
microlenses when limited space is available, such as in displays.
Examples of this technology include the brightness enhancing films
from 3M corporation that have 20 to 50 micron prisms molded into
their surface. In suitable embodiments, the present invention
provides microlenses comprising luminescent nanocrystals
hermetically sealed in an encapsulating polymer (or in a container)
which is then micropatterned such that a microlens is formed. For
example, as shown in FIG. 5, microlens assembly 500 suitably
comprises hermetically sealed composition 502 comprising a layer
504 of luminescent nanocrystals 104 placed on top of, or otherwise
in contact with, LED 506 which is supported by substrate 508. The
surface of composition 502 can be molded into various shapes, for
example to include a series of microprisms 510, as shown in FIG. 5,
thereby forming the microlens.
[0083] In exemplary embodiments, use of a microlens in combination
with the hermetically sealed compositions of the present invention
allow for an increase in the amount of emitted light captured (and
therefore emitted from the composition) from the LED/luminescent
nanocrystals. For example, the addition of microprisms or other
microlens assembly to the hermetically sealed compositions and
containers of the present invention suitably leads to an increase
in the amount of light captured of greater than about 10% (e.g.,
about 10-60%, about 10-50%, about 10-40%, about 20%-40%, or about
30-40%) as compared to a composition that does not comprise
microprisms or other microlens assembly. This increase in the
amount of light captured correlates directly to an increase in the
total amount of light that is emitted from the composition or
container.
[0084] In suitable embodiments, a dichroic minor can be attached or
otherwise associated with the containers/compositions that forms a
lens for application over a light source. A dichroic minor allows a
particular wavelength of light to pass through the mirror, while
reflecting others. As light from the source enters the lens-shaped
containers/compositions, the photons are able to enter the
containers/compositions and excite the various luminescent
nanocrystals that have been hermetically sealed inside. As the
luminescent nanocrystals emit light, photons are able to exit the
containers/compositions, but not reflect back toward the initial
light source (as they are reflected by the dichroic mirror). In
embodiments then, suitable containers/compositions can be created
to fit over a light source (e.g., an LED). This allows light to
enter from the source and excite the luminescent nanocrystals
inside, but emitted light is only allowed to exit the
containers/compositions away from the light source, blocked from
reflecting back into the source by the dichroic mirror. For
example, blue light from an LED source is allowed to pass through
the dichroic minor and excite encapsulated luminescent
nanocrystals, which then emit green light. The green light is
reflected by the mirror and not allowed to reflect back into the
light source.
[0085] As discussed herein, in suitable embodiments the
hermetically sealed luminescent nanocrystal compositions of the
present invention are used in combination with an LED or other
light source. Applications for these sealed nanocrystal/LEDs are
well known to those of ordinary skill in the art, and include the
following. For example, such sealed nanocrystal/LEDs can be used in
microprojectors (see, e.g., U.S. Pat. Nos. 7,180,566 and 6,755,563,
the disclosures of which are incorporated by reference herein in
their entireties); in applications such as cellular telephones;
personal digital assistants (PDAs); personal media players; gaming
devices; laptops; digital versatile disk (DVD) players and other
video output devices; personal color eyewear; and head-up or
head-down (and other) displays for automobiles and airplanes. In
additional embodiments, the hermetically sealed nanocrystals can be
used in applications such as digital light processor (DLP)
projectors.
[0086] In additional embodiments, the hermetically sealed
compositions and containers disclosed throughout can be used to
minimize the property of an optical system known as etendue (or how
spread out the light is in area and angle). By disposing, layering
or otherwise covering (even partially covering) an LED or other
light source with a composition or container of the presently
claimed invention, and controlling the ratio of the overall area
(e.g, the thickness) of the luminescent nanocrystal composition or
container to the area (e.g., the thickness) of the LED, the amount
or extent of etendue can be minimized, thereby increasing the
amount of light captured and emitted. Suitably, the thickness of
the luminescent nanocrystal composition or container will be less
than about 1/5 the thickness of the LED layer. For example, the
luminescent nanocrystal composition or container will be less than
about 1/6, less than about 1/7, less than about 1/8, less than
about 1/9, less than about 1/10, less than about 1/15 or less than
about 1/20 of the thickness of the LED layer.
[0087] In further embodiments, the hermetically sealed luminescent
nanocrystals of the presently claimed invention can be used in a
system 602 comprising a light-focusing apparatus (or focusing
apparatus) 604, for example, as shown in FIGS. 6A-6C. In exemplary
embodiments, a light-focusing apparatus 604 is prepared and
attached or otherwise associated with an LED 506. Suitably,
light-focusing apparatus 604 is in the shape of a cube or
rectangular box, where the bottom of the box situated on or above
the LED 506, with the sides of the apparatus extending above the
LED. FIG. 6A shows a cross sectional view of apparatus 604, taken
through plane 1-1 of FIG. 6B, showing a top view of the apparatus
604, LED 506 and substrate 508. In exemplary embodiments, apparatus
604 comprises four sides surrounding LED 506, though in other
embodiments any number of sides can be used (e.g., 2, 3, 4 5, 6, 7,
8, 9, 10, etc.), or a circular apparatus can be used, such that
only a single piece (or multiple pieces fashioned for form a
continuous piece) of material surrounds LED 506. In general, the
top and bottom of light-focusing apparatus 604 are open (i.e., the
apparatus is placed directly on top of and encloses LED 506),
though in other embodiments, either the top or bottom, or both, of
apparatus 604 can be closed by an additional piece of material.
[0088] Focusing apparatus 604 suitably is made of a material that
can reflect light that is generated by LED, or is coated with a
material that reflects light. For example, focusing apparatus can
comprise a polymer, metal, ceramic, etc. In other embodiments, the
inner surface (i.e., the surface facing LED) can be coated with a
reflective material such as a metal (e.g, Al) or other reflective
coating. This reflective coating can be deposited on the surfaces
of focusing apparatus using any suitable method, such as spray
coating, ALD, painting, dipping, spin coating, etc.
[0089] Focusing apparatus 604 suitably encloses or encapsulates a
hermetically sealed nanocrystal composition 504 (or hermetically
sealed nanocrystal container) of the present invention, and thus
the apparatus is associated with the composition or container. In
suitable embodiments, focusing apparatus 604 can be prepared
separately from LED 506 and then attached to the LED, for example
by an adhesive such as an epoxy, and then the center portion of the
apparatus 604 filled in with a hermetically sealed nanocrystal
composition 504. In further embodiments, focusing apparatus 604 can
be directly assembled on LED 506. In other embodiments, a
hermetically sealed composition can be disposed on LED and then
focusing apparatus can be added, either as a pre-made apparatus, or
constructed directly on the LED. In suitable embodiments, apparatus
604 also comprises a cover (e.g., a glass or polymer cover) to seal
the nanocrystal composition 504. Such a cover can act as a hermetic
seal over the nanocrystal composition, or simply as an additional
structural element to support the nanocrystal composition and the
focusing apparatus. Such a cover can be placed directly on top of
nanocrystal composition 504, or can be placed at the top of
apparatus 604, or in any position in between.
[0090] As shown in FIGS. 6A and 6C, in suitable embodiments,
focusing apparatus 604 is prepared in such a manner that the sides
of the apparatus taper inward at the bottom (e.g., near the LED),
but outward at the top (away from the LED). This helps to aid in
gathering and focusing the light 606 into a beam so as to direct
the light out of the apparatus. As shown FIG. 6C, suitably focusing
apparatus 604 directs light 606 out from the LED. By using tapered
or angled sides, light 606 that is emitted from the
LED/nanocrystals is directed out of the apparatus 604, rather than
lost either by bouncing back and forth inside of the apparatus, or
lost simply unable to escape. Use of light-focusing apparatus in
combination with the luminescent nanocrystal compositions and
containers of the present invention can suitably be employed in
microprojectors and other applications where a focus, beam of light
is desired or required.
Light-Emitting Diode (LED) Devices with Hermetically Sealed
Nanocrystals
[0091] In a further embodiment, the present invention comprises
light-emitting diode (LED) devices. An exemplary LED device 700 is
shown in FIG. 7A. LED device 700 suitably comprises an LED 702. LED
702 is shown on substrate 706 for illustrative purposes only. It
should be understood that any suitable configuration of an LED can
be utilized in the practice of the present invention. In addition,
multiple (i.e., more than one) LED can be utilized in LED device
700. LED device 700 further comprises a hermetically sealed
container 708 comprising a plurality of luminescent nanocrystals
710. Container 708 is optically coupled to LED 702. LED device 700
also comprises a light guide 712 optically coupled to hermetically
sealed container 708.
[0092] In embodiments of the present invention, a first portion of
light emitted from the LED is down-converted by the luminescent
nanocrystals 710. A second portion of light emitted from the LED
and the down-converted light from the luminescent nanocrystals are
emitted from light guide 712.
[0093] Any suitable LED can be utilized in the LED devices of the
present invention, including various configurations of LEDs, and
LEDs emitting light over the entire visible spectrum, as well as
LEDs that emit ultraviolet light (light with a wavelength of 10 nm
to about 380 nm). Suitably, LED 702 emits blue light. As described
herein, the visible spectrum includes light having wavelengths
between about 380 nm and about 780 nm that is visible to the human
eye. Visible light can be separated into the various colors of the
spectrum, such as red, orange, yellow, green, blue, indigo and
violet. As used herein, blue light comprises light between about
435 nm and about 500 nm, green light comprises light between about
520 nm and 565 nm, more suitably about 525 nm to about 530 nm, and
red light comprises light between about 625 nm and about 740 nm in
wavelength, more suitably about 625 nm to about 640 nm.
[0094] Suitably, as shown in FIG. 7B, LED 702 emits blue light 716.
A first portion 718 of the blue light emitted from the LED is
down-converted by luminescent nanocrystals 710. As the nanocrystals
absorb this portion of blue light and then emit light at a second
wavelength 722, 724 (see FIG. 7B). Suitably, the light emitted from
nanocrystals 710 comprises light having wavelengths primarily in
the green (e.g, between about 520 nm and 565 nm, more suitably
about 525 nm to about 530 nm) and red (e.g, between about 625 nm
and about 740 nm in wavelength, more suitably about 625 nm to about
640 nm) ranges. Thus, suitably nanocrystals 710 comprise two
populations of nanocrystals. One population of nanocrystals is
designed to absorb blue light and emit red light, and a second
population of nanocrystals is designed to absorb blue light and
emit green light. The populations of nanocrystals suitably comprise
a plurality (i.e., 2 or more, 10 or more, 100 or more 1000 or more,
etc.) of nanocrystals. As described herein, the ability to tailor
the composition and size of the nanocrystals allows for the design
of nanocrystals having specific absorption and emission
characteristics.
[0095] "A first portion" of blue light 718 refers to a percentage
of the blue light 716 emitted from LED that is down-converted from
blue to another wavelength(s) of light. A first portion can be any
amount of the original blue light 716 emitted from LED 702 that is
less than the total amount of blue light given off by the LED
(e.g., about 99% to about 1% of the blue light emitted from LED
702, suitably about 80% to about 30%, about 70% to about 40%, about
70% to about 50% or about 60%).
[0096] A second portion 720 of blue light emitted from LED 702
passes through hermetically sealed container 708, emerging as blue
light (suitably about 20% to about 50%, or about 20% to about 40%).
This second portion of blue light 720 and the down-converted light
722 and 724 emitted from the nanocrystals (e.g., red light and
green light) are then emitted 726 from the light guide 712. The
blue light emitted from the LED 720, and the down-converted green
light and red light (722 and 724) suitably combine to produce white
light 726 when ultimately emitted from the light guide.
[0097] In further embodiments, two (or more) blue light emitting
LEDs can be utilized, so that all of the light from one (or more)
LED is down-converted by the nanocrystals, while all of the light
from the second (third, etc.) LED passes through the hermetically
sealed container, resulting in the red, green and blue wavelengths
that combine to produce white light.
[0098] Hermetically sealed container 708 is suitably a plastic or
glass container. Exemplary hermetically sealed containers are
described throughout. In suitable embodiments, the hermetically
sealed container is a plastic or glass (e.g., borosilicate)
capillary. As used herein "capillary" refers to an elongated
container having a length dimension that is longer than both its
width and height dimension. Suitably, a capillary is a tube or
similar structure having a circular, rectangular, square,
triangular, irregular, or other cross-section. Suitably, a
capillary for use in the LED devices of the present invention can
be configured so as to match the shape and orientation of the LED
to which it is optically coupled. In exemplary embodiments, a
capillary has at least one dimension of about 100 .mu.m to about 1
mm. In embodiments in which a plastic capillary it utilized, a
coating such as SiO.sub.2, AlO.sub.2 or TiO.sub.2, as well as
others described herein, can be added so as to provide an
additional hermetic seal to the capillary.
[0099] Suitably, a capillary of the present invention has a
thickness of about 50 .mu.m to about 10 mm, about 100 .mu.m to
about 1 mm, or about 100 .mu.m to about 500 .mu.m. Thickness refers
to dimension of the capillary into the plane of the light guide.
Suitably, a capillary of the present invention has a height (in the
plane of the light guide) of about 50 .mu.m to about 10 mm, about
100 .mu.m to about 1 mm, or about 100 .mu.m to about 500 .mu.m.
Suitably, a capillary of the present invention has a length (in the
plane of the light guide) of about 1 mm to about 50 mm, about 1 mm
to about 40 mm about 1 mm to about 30 mm about 1 mm to about 20 mm
about 1 mm to about 10 mm.
[0100] In still further embodiments a hermetically sealed
composition of luminescent nanocrystals as described herein can be
utilized in the LED devices. In such embodiments, the hermetically
sealed composition is optically coupled to the LED and the light
guide, and thus provides the down-converted light from the
nanocrystals.
[0101] As used herein a "light guide" refers to an optical
component that is suitable for directing electromagnetic radiation
(light) from one position to another. Exemplary light guides
include fiber optic cables, polymeric or glass solid bodies such as
plates, films, containers, or other structures. The size of the
light guide will depend on the ultimate application and
characteristics of the LED devices. In general, the thickness of
the light guide will be compatible with thickness of the LED. The
other dimensions of the light guide are generally designed to
extend beyond the dimensions of the LED, and are suitably on the
order of 10s of millimeters, to 10s to 100s of centimeters. While
the light guides illustrated in the Figures represent embodiments
suitable for use in display systems and the like, other light
guides, including fiber optic cables, etc., can also be
utilized.
[0102] Exemplary nanocrystals for use in the practice of the
present invention are described herein. In suitable embodiments,
the nanocrystals are core/shell nanocrystals. Suitably, the
nanocrystals contain one or more ligands attached to their surface
that increase the solubility of the nanocrystals in a polymeric
material. Exemplary ligands are described herein and in U.S. patent
application Ser. No. 11/034,216, U.S. patent application Ser. No.
10/656,910 and U.S. Provisional Patent Application No. 60/578,236.
Exemplary sizes of the nanocrystals are also described herein.
[0103] In suitable embodiments, the luminescent nanocrystals
comprise CdSe or ZnS. Exemplary core/shell nanocrystals that can be
utilized include CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS
and CdTe/ZnS, nanocrystals. In exemplary embodiments, as described
herein, the nanocrystals are dispersed or embedded in a polymeric
matrix. This matrix can then be drawn into, or otherwise disposed
in, a capillary, prior to sealing the capillary.
[0104] In additional embodiments, a scattering material (e.g.,
particles of material that scatter light entering the hermetically
sealed containers) can be added to the matrix. Suitably, the
scattering media are metallic, polymeric, semiconductor, or other
material particles on the order of 500 nm to microns to even
millimeters in size. In other embodiments, a scattering material
can be placed between the LED and the hermetically sealed
container, or between the container and the light guide.
[0105] The concentration of nanocrystals in the hermetically sealed
container will depend on the application, size of the nanocrystals,
composition of the nanocrystals, composition of the polymeric
matrix, and other factors, and can be optimized using routine
methods in the art. Suitably, the luminescent nanocrystals are
present at a concentration of about 0.01% to about 50%, about 0.1%
to about 50%, about 1% to about 50%, about 1% to about 40%, about
1% to about 30%, about 1% to about 20%, about 1% to about 10%,
about 1% to about 5%, or about 1% to about 3%, by weight. Suitably,
about 40% to about 80%, more suitably about 50% to about 70%, or
about 60%, of the light from the LEDs is absorbed by the
nanocrystals, with the remaining light suitably passing through the
hermetically sealed container. Suitably about 10% to about 40%, or
about 20% to about 30% of the light that impacts the container
passes through the container without being down-converted.
[0106] As described herein, hermetically sealed container 708 is
optically coupled to both LED 702 as well as light guide 712. As
used herein, "optically coupled" means that a component, (e.g.,
hermetically sealed container and LED) are positioned so that light
is able to pass from one component to another component without
substantial interference. Optical coupling includes embodiments in
which hermetically sealed container 708 and LED 702 are in direct
physical contact, or as shown in FIG. 7A, suitably hermetically
sealed container 708 (and thus nanocrystals 710) and LED 702 are
spaced apart by a distance 704. While hermetically sealed container
708 is shown in FIG. 7A contacting the top of substrate 706, any
suitable configuration can be utilized, so long as light from LED
is able to pass to hermetically sealed container 708. For example,
hermetically sealed container can be positioned within the space
between the top of substrate 706 and LED 702. In other embodiments,
an optically transparent element (e.g., a glass or plastic sheet or
strip, including a lens) can be placed between hermetically sealed
container 708 and LED 704. It should be noted that optical coupling
does not require physical interaction between the components.
Rather, so long as light is able to pass between the components
they are considered optically coupled. The spacing between
hermetically sealed container 708 and LED 702 results in the
nanocrystals being remotely positioned from the LED. This remote
location improves the characteristics (intensity, purity, color
rendering, etc.) of the light generated from the LED and the
nanocrystals.
[0107] In embodiments, light guide 712 is optically coupled to the
hermetically sealed container 708 via glue, tape mechanical
alignment alone, or the like, and combinations thereof. As shown in
FIG. 7A, suitably light guide 712 is directly in contact with
hermetically sealed container 708. Tape, glue or other fastening
device can be utilized to maintain the physical contact between the
two elements. Suitably fastening device is optically transparent,
or substantially optically transparent, so as allow light to pass
from the hermetically sealed container to the light guide. This can
also be accomplished, for example, by utilizing a polymeric light
guide, that when heated, melts or deforms such that hermetically
sealed container can be contacted to the light guide, and then the
light guide cooled, thereby facilitating the formation of a
physical adhesion or contact between the two elements.
[0108] FIGS. 8A-8C show additional configurations of the LED device
described in FIG. 7A. In FIG. 8A, light guide 712 is shown with a
tapered edge 802. Tapered edge 802 can help facilitate directing
the light emitted from the LED and the nanocrystals into light
guide 712. In FIG. 8B, hermetically sealed container 708 can be
embedded into light guide 712, as shown at 804. This can be
accomplished by, for example, removing a section of light guide 712
such that hermetically sealed container can be directly inserted
into light guide 712. In other embodiments, as noted above, light
guide 712 can be heated so as to melt or deform, thereby allowing
hermetically sealed container 708 to be inserted or embedded into
light guide 712. As illustrated in FIG. 8C, in further embodiments,
hermetically sealed container 708 can be shaped, as shown in 806.
In exemplary embodiments, hermetically sealed container 708 can be
shaped so as to act as a lens or other optical device to improve
light transfer from the LED to the light guide.
[0109] FIG. 9 shows an embodiment of an LED device of the present
invention in which the device further comprises one or more
reflectors 902 positioned with respect to the LED, light guide and
hermetically sealed container, so as to increase the amount of
light that is emitted from the light guide. As shown in FIG. 9, in
exemplary embodiments a reflector can be positioned behind the LED
so as to reflect any light emitted from the nanocrystals in the
hermetically sealed container that is not directed into the light
guide, or light that bounces back from LED. Similarly, the sides of
the hermetically sealed container can also comprise reflectors 902
so as to reflect light toward the light guide. In additional
embodiments, the substrate on which the LED is positioned can also
comprise reflective, angled sides that help to direct light from
the LED into the hermetically sealed container.
[0110] FIGS. 10A-10B provide illustrations of an exemplary
hermetically sealed container 708, e.g., a capillary. As shown in
FIG. 10B, in embodiments, the end of hermetically sealed container
708 (capillary) can be capped with a cap 1002. Cap 1002 is suitably
made from a polymeric material that can be heated prior to
application, and then cooled so as to seal the hermetically sealed
container. In other embodiments, a liquid polymeric solution can be
used to fill the end of the hermetically sealed container, thereby
sealing the container. Additional methods of sealing the
hermetically sealed container, as described herein or otherwise
known in the art, for example crimping, pinching, laser sealing,
heat shrinking or otherwise closing the end of the container, can
also be used.
[0111] Suitably, a solution of luminescent nanocrystals dispersed
in a polymeric matrix is drawn into a capillary, for example by
using a vacuum to generate a reduced pressure. The polymer is then
suitably cooled and cured. The curing process can often result in
small bubbles forming in the polymeric matrix. It has been
discovered that the small size of the bubbles in these preparations
does not interfere with the optical properties of the composition
or the nanocrystals, and in fact, the presence of these small
bubbles may aid in reducing pressure that builds when the matrix is
thermally cycled during manufacturing or use with an LED.
[0112] In suitable embodiments, the present invention provides
white light light-emitting diode (LED) devices. Such devices
suitably comprise a blue light light-emitting LED and a
hermetically sealed container comprising a plurality of luminescent
nanocrystals (suitably CdSe/ZnS luminescent nanocrystals) optically
coupled to the LED. The device also comprises a light guide
optically coupled the hermetically sealed container.
[0113] As illustrated in FIG. 7B, as a first portion of blue light
718 emitted from the LED enters the hermetically sealed container,
the light is down-converted by the luminescent nanocrystals (e.g.,
CdSe/ZnS luminescent nanocrystals) to green light and red light
(722 and 724). A second portion of blue light emitted from the LED
720, the green light and the red light, are emitted from the light
guide and combine to produce white light 726.
[0114] As described herein, the white light LED devices of the
present invention suitably comprise a hermetically sealed container
comprising luminescent nanocrystals spaced apart (remote) from the
LED. The concentration of nanocrystals within the hermetically
sealed container is provided such that a portion of the blue light
emitted by the LED is able to pass through the container without
being absorbed by the nanocrystals. Another portion of the blue
light is absorbed, and then down-converted by the nanocrystals and
emitted as green and red light. The red, blue and green light then
combine to produce white light when emitted from the light guide.
The approach of the present invention differs from white light LEDs
in which three separate light sources (e.g., three LEDs) are
utilized, or where all of the blue light from the LED is absorbed
by the luminescent nanocrystals. By optimizing the
concentration/density and characteristics of the nanocrystals, high
intensity, high purity, precisely color tuned, white light can be
produced.
[0115] In further embodiments, the present invention provides
light-emitting diode (LED) devices, comprising an LED, a
hermetically sealed container comprising a plurality of luminescent
nanocrystals optically coupled to the LED, and a light guide
optically coupled to the hermetically sealed container. Light
emitted from the LED is down-converted by the nanocrystals, and
exits a surface of the light guide. Suitably, the luminescent
nanocrystals emit blue, green and red light, and the light combines
to produce white light. In such embodiments, the LED suitably emits
ultraviolet light.
[0116] In further embodiments, the present invention provides
display systems comprising the LED devices described herein.
Suitably, as shown in FIG. 11, the display systems 1100 comprise a
display 1102, and a plurality of LED devices 700. As described
herein, suitably LED devices 700 comprise an LED 702 and a
hermetically sealed container 708 comprising a plurality of
luminescent nanocrystals optically coupled to the LED. The devices
also comprise a light guide 712 optically coupled to the
hermetically sealed container. As shown in FIG. 11, suitably,
display 1102 at least partially encloses light guide 712.
[0117] In embodiments, down converted light emitted from the
luminescent nanocrystals is emitted from the light guide and
displayed on the display. The display systems of the present
invention are capable of emitting light over the full range of the
visible spectrum, including white light.
[0118] In further embodiments, a first portion of light emitted
from the LED is down-converted by the luminescent nanocrystals. A
second portion of light emitted from the LED and the down-converted
light from the luminescent nanocrystals are emitted from the light
guide and displayed on the display. The display systems of the
present invention are capable of emitting light over the full range
of the visible spectrum, including white light. In exemplary
embodiments, the LEDs utilized emit blue light.
[0119] Exemplary hermetically sealed containers (including
capillaries) and luminescent nanocrystals are described herein. As
shown in FIG. 11, suitably a single hermetically sealed container
708' is optically coupled to at least two LEDs. A single
hermetically sealed container can be optically coupled to two or
more, three or more, four or more, five or more, ten or more, etc.,
LEDs. While a hermetically sealed container 708 can be coupled to
each individual LED, in the display system embodiments of the
present invention, use of a single hermetically sealed container
which is coupled to multiple LEDs allows for easier assembly and
manufacture of the display systems. In embodiments in which a
single hermetically sealed container is coupled to multiple LEDs,
each LED suitably emits blue light, a portion of which is
down-converted by the nanocrystals in the container, and a portion
of which is emitted from the light guide. While FIG. 11
demonstrates an embodiment in which a single light guide and a
single display are utilized, it should be understood that the
display systems of the present invention can comprise multiple
light guides and multiple displays optically coupled to each other
to result in a display system.
[0120] The hermetically sealed containers comprising luminescent
nanocrystals as described herein can be utilized to retrofit
existing LED display systems. By including the hermetically sealed
containers (e.g., capillaries) between the LEDs and light guides of
a display, a portion light from the LEDs (suitably blue light) can
be converted to any desired color, including combining with the LED
light to produce white light.
[0121] Table 1 below shows the light output from luminescent
nanocrystals of the present invention, as well as light from the
blue LED used to excite the nanocrystals. The nanocrystals were
spaced apart from the LED (remote from the LED) as described
herein. Data is also shown for traditional Yttrium Aluminum Garnet
(YAG) phosphors. FWHM=full width at half maximum.
TABLE-US-00001 TABLE 1 Spectrum Characteristics YAG Luminescent
Nanocrystals Blue Peak (nm) 451.8 463.5 Blue FWHM (nm) 21.6 21.6
Green Peak (nm) N/A 535.3 Green FWHM (nm) N/A 32.8 Yellow Peak (nm)
559 N/A Yellow FWHM (nm) 105 N/A Red Peak (nm) N/A 614.5 Red FWHM
(nm) N/A 44.5
Luminescent Nanocrystal Composites
[0122] In a still further embodiment, the present invention
luminescent nanocrystal composite materials 1200. As shown in FIG.
12, in embodiments, the composite materials comprise a first
polymeric material 1204 having a first composition, a second
polymeric 1202 material having a second composition, and a
plurality of luminescent nanocrystals 710 dispersed in second
polymeric material 1202. The, second polymeric material 1202 is
dispersed in first polymeric material 1204.
[0123] Dispersing luminescent nanocrystals in second polymeric
material 1202 provides a method to seal the nanocrystals and
provide a mechanism for mixing various compositions and sizes of
nanocrystals. Suitable second polymeric materials 1202 include
aminosilicone, as well as other polymers described herein,
including, but not limited to, poly(vinyl butyral):poly(vinyl
acetate); epoxies; urethanes; silicone and derivatives of silicone,
including, but not limited to, polyphenylmethylsiloxane,
polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane,
fluorinated silicones and vinyl and hydride substituted silicones;
acrylic polymers and copolymers formed from monomers including but
not limited to, methylmethacrylate, butylmethacrylate and
laurylmethacrylate; styrene based polymers; and polymers that are
cross linked with difunctional monomers, such as
divinylbenzene.
[0124] While second polymeric material 1202 provides a suitable
environment for dispersing the nanocrystals, the polymers that
provide efficient mixing of the nanocrystals can often be brittle
or difficult to shape or mold. Dispersing the nanocrystal/polymer
mixture 1202 in a further polymeric material 1204 allows for the
production of a composite that maintains the desired
optical/down-conversion characteristics of the luminescent
nanocrystals, while also maintaining a hermetically sealed
composition that is also able to be mechanically worked as desired.
Exemplary polymeric materials for use as first polymeric material
1204 include epoxies and polycarbonates. Exemplary epoxies and
polycarbonates are well known in the art.
[0125] Suitably the luminescent nanocrystals dispersed in the
composite materials absorb light (e.g., blue light) and emit green
light and/or red light, though other colors can also be emitted
from the nanocrystals. Exemplary nanocrystals for use in the
composite materials are described herein and include nanocrystals
comprise that CdSe or ZnS, as well as core/shell luminescent
nanocrystals comprising CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS,
CdTe/CdS or CdTe/ZnS.
[0126] In further embodiments, the composites can comprise an
inorganic layer 1206 that hermetically seals the composite.
Examples of inorganic layers are described herein, and include,
SiO.sub.2, TiO.sub.2 or AlO.sub.2.
[0127] Suitably, the composite materials of the present invention
have an optical density of about 0.5 to about 0.9 at the blue LED
wavelength and a path length of about 50 .mu.m to about 200 .mu.m.
Suitably, the composites have an optical density of about 0.5 to
about 0.8, about 0.7 to about 0.8, or about 0.8 at the blue LED
wavelength. Suitably, the path length of the composite materials is
about 75 .mu.m to about 150 .mu.m, or about 100 .mu.m. The
concentration of luminescent nanocrystals utilized in the composite
materials of the present invention is suitably about the same as
the concentration utilized in the hermetically sealed compositions
described herein. Thus, the luminescent nanocrystals are suitably
present at a concentration of about 0.01% to about 50%, about 0.1%
to about 50%, about 1% to about 50%, about 1% to about 40%, about
1% to about 30%, about 1% to about 20%, about 1% to about 10%,
about 1% to about 5%, or about 1% to about 3%, by weight, such that
about 40% to about 80%, more suitably about 50% to about 70%, or
about 60%, of the light that impacts the composite is absorbed by
the nanocrystals.
[0128] The present invention also provides methods of preparing
luminescent nanocrystal composite materials. As shown in flowchart
1300 of FIG. 13, with reference to FIG. 12, suitably such methods
include step 1302, comprising dispersing a plurality of luminescent
nanocrystals 710 in a first polymeric material 1202 to form a
mixture of the luminescent nanocrystals and the first polymeric
material. The mixture is then cured in 1304. In 1308, a particulate
is generated from the cured mixture. In step 1310, the particulate
is dispersed in a second polymeric material 1204 to generate a
composite material. The particulate can be dispersed in the second
polymeric material using various forms of mechanical mixing when
the second polymeric material is in a liquid, or mostly liquid,
state.
[0129] Exemplary polymeric materials for use in the methods are
described herein, as are suitable luminescent nanocrystals.
Suitably, the luminescent nanocrystals comprise CdSe or ZnS, or are
core shell nanoparticles comprising CdSe/ZnS, InP/ZnS, PbSe/PbS,
CdSe/CdS, CdTe/CdS or CdTe/ZnS, and are suitably dispersed in
aminosilicone.
[0130] Suitably the mixture of luminescent nanocrystals and the
first polymeric material are mechanically processed to form the
particulate. Examples of mechanical processing include ball
milling, grinding, pulverizing, crushing or otherwise forming a
particulate from the mixture. Chemical or other treatments can also
be utilized to generate a particulate. Suitably the particulate is
a powder. Suitably, the particulate of the mixture of the
nanocrystals and the first polymeric material has a size on the
order of about 10 .mu.m to about 200 .mu.m, or about 10 .mu.m to
about 100 .mu.m, or about 20 pm to about 70 .mu.m, or about 50
.mu.m.
[0131] Other structures of the mixture of the luminescent
nanocrystals and the first polymeric material beyond particulates
can also be generated, for example, films, rods, ribbons, spheres,
etc. These structures can then be dispersed in the second polymeric
material.
[0132] In further embodiments, the second polymeric material can be
replaced with other materials, such as ceramics, glasses, or
inorganic materials that have the desired optical and physical
properties of the final desired product.
[0133] In exemplary embodiments, a cross-linker is added in step
1306 to the mixture prior to the curing in 1304. Exemplary
cross-linkers are described herein or otherwise known in the
art.
[0134] In further embodiments, as shown in FIG. 13, the methods can
further comprise step 1312 of forming the composite material into a
film. Suitably, the composite mixture is cast onto a substrate,
such as a non-stick substrate, for example a sheet of TEFLON.RTM..
After the mixture has been cured, the cured film can be removed
from the non-stick substrate. The film can then be cut or diced
into any desired size or shape.
[0135] In additional embodiments, as shown in step 1314 of
flowchart 1300, an inorganic layer can be disposed on the composite
so as to provide a further hermetic seal to the composite. The
inorganic layer can be disposed after formation of the composite
material, but prior to formation of the composite into a film, or
the inorganic layer can be disposed following the film formation
(including following dicing/cutting into a desired shape). Methods
of disposing an inorganic layer on the composite are described
herein, and include various methods of coating, spraying, ALD,
dipping etc.
[0136] The composite material can also be extruded, molded, solvent
cast, compression molded, etc., to form the desired shape and
configuration of the composite. Methods and parameters for carrying
out these techniques are well known in the art.
[0137] The composite materials of the present invention can be
utilized in the down-converting applications as described herein,
or in other applications where a down-converting
layer/film/structure is desired. Thus, in exemplary embodiments, a
layer, film, tube, strip or other suitable structure can be
prepared from the composite materials and optically coupled to an
LED (and/or a light guide) so as to provide the down-conversion of
light from an LED as described herein.
Light Guides Comprising Nanocrystals
[0138] In a still further embodiment, the present invention
provides light-emitting diode (LED) devices as shown in FIGS.
14A-14B. Suitably, LED devices 1400 and 1401 comprise an LED 702,
and a light guide 712 optically coupled to the LED. A plurality of
luminescent nanocrystals 710 are dispersed in a region (1404,
1404') within the light guide. Suitably, the region extends along a
length 1410 of the light guide. Suitably, the nanocrystals emit
blue light, red light and green light. In embodiments, the LED is
an ultraviolet (UV) light emitting LED.
[0139] In further embodiments, a first portion of light emitted
from the LED is down-converted by the nanocrystals. As shown in
FIGS. 14A and 14B a second portion of light (1412) emitted from the
LED, and the down-converted light (1414 and 1416), exit a surface
of the light guide.
[0140] As described throughout, luminescent nanocrystals of the
present invention suitably absorb light of a specified wavelength
and then down-convert the absorbed light, emitting light at a
different wavelength. In the embodiments of the present invention
illustrated in FIGS. 14A-14B, the luminescent nanocrystals 710 are
dispersed in a region 1404 and 1404' of the light guide. Light that
is emitted from the LED travels through the length of the light
guide 1410, suitably reflecting off of reflectors along the surface
of the light guide. In embodiments, a portion of the light emitted
from the LED is emitted from the surface of the light guide as
shown at 1412. A further portion of the light emitted from the
light guide is absorbed by the luminescent nanocrystals and
down-converted. This down converted light (1414 and 1416) is then
emitted from the light guide. In further embodiments, all of the
light emitted from the LED is down-converted by the
nanocrystals.
[0141] In exemplary embodiments, the LED is a blue light emitting
LED. As discussed in detail herein, in exemplary embodiments, a
portion of the blue light emitted from the LED is down-converted by
the luminescent nanocrystals into red light and green light. When
the emitted green 1414 and red 1416 light combine with the portion
of blue light 1412 emitted from the LED (that has not been
down-converted), white light is emitted from the surface of the
light guide. In suitable embodiments, light guide 712 comprises one
or more features 1406 on the emitting surface(s) of the light
guide. Features 1406 are suitably patterns etched into, or formed
from, the surface of light guide 712 that aid in the transmission
of light from the light guide. In embodiments, features 1406 are
designed to enhance the emission of light that is emitted directly
from the LED (including blue light).
[0142] In further embodiments, the LED is a UV light emitting LED,
and substantially all of the light emitted from the LED is
down-converted by the nanocrystals to red, green and blue light.
The light is then emitted from the light guide and combines to
produce white light.
[0143] Exemplary nanocrystals for use in the regions within the
light guides are described herein. Suitably, the nanocrystals CdSe
or ZnS, or are core/shell nanocrystals, suitably comprising
CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.
[0144] As used herein, "region" refers to a section or portion of
the light guide into which luminescent nanocrystals have been
disposed. Suitably, as shown in FIGS. 14A-14B, regions 1404 and
1404' extend along the length 1410 of light guide 712. The length
1410 of the light guide is the lateral dimension extending
perpendicular (or substantially perpendicular) to the LED. By
orienting light guide 712 with respect to LED 702 as shown in FIGS.
14A and 14B, light from LED 702 impacts a greater portion of the
nanocrystals 710 within the regions 1404 and 1404' prior to exiting
the light guide. Suitably, region 1404/1404' is a layer of
luminescent nanocrystals. The dimensions of region 1404/1404' are
dictated by the overall dimensions of the light guide, though
generally the thickness of the region will be in proportion to the
size of the LED (i.e., on the order of 10s of microns to 10s of
millimeters or so), while the dimensions in the plane of the light
guide (i.e., length and width), suitably span the entire light
guide. In other embodiments, the region comprising the nanocrystals
can be throughout the entire light guide in all dimensions (i.e.,
dispersed throughout the light guide).
[0145] Region 1404/1404' can be generated by dispersing
nanocrystals in a polymeric matrix and then forming the light guide
around the polymer either prior to or after curing the polymer.
Alternatively, the light guide can be prepared and then
nanocrystals injected, painted, sprayed, or otherwise deposited so
as to form the region. Other methods for generating a polymeric
matrix, including the methods described herein with regard to
formation of polymeric composites can also be utilized to form the
regions. In exemplary embodiments, the luminescent nanocrystal
composite materials 1200 described herein can be utilized to
prepare the regions in the light guides.
[0146] Dispersing luminescent nanocrystals in a region within the
light guide provides numerous benefits and advantages to the
overall system. For example, more uniform illumination of the
nanocrystals can be achieved, thereby reducing the presence of
local hot spots. Dispersing the nanocrystals throughout the region
allows for improved heat dissipation from the nanocrystals, thus
lowering the overall temperature of the nanocrystals. By reducing
the optical path length from the nanocrystals to the top surface of
the light guide, any loss in efficiency due to reabsorption of
green and red photons is reduced. In addition, a low concentration
of nanocrystals can be utilized in the region, thus lowering
possible photo- and thermal-induced interactions between
nanocrystals and the material in which the nanocrystals are
dispersed (e.g., a polymer), thereby increasing system
life-time.
[0147] The concentration of luminescent nanocrystals in the region
of the light guide will depend on the application, size of the
nanocrystals, composition of the nanocrystals, composition of the
polymeric matrix, and other factors, and can be optimized using
routine methods in the art. Suitably, the luminescent nanocrystals
are present at a concentration that is less than the concentration
utilized in the LED device embodiments described herein utilizing a
hermetically sealed container, suitably about 0.01% to about 50%,
about 0.1% to about 50%, about 1% to about 50%, more suitably about
1% to about 40%, about 1% to about 30%, about 1% to about 20%,
about 1% to about 10%, about 1% to about 5%, or about 1% to about
3%, by weight. In general, the concentration of luminescent
nanocrystals scales proportionally based on the size of the light
guide. Thus, the concentration of luminescent nanocrystals utilized
in a hermetically sealed container having a thickness of
approximately 100 mm will be reduced by two orders of magnitude for
a light guide that is about 10 cm in length, for example.
[0148] In exemplary embodiments, region 1404' has a thickness that
varies along the length 1410 of the light guide. As shown in FIG.
14B, suitably the thickness of region 1404' increases along the
length 1410 of the light guide, from a minimum 1406 at the LED, to
a maximum at the far end of the light guide 1408, away from the
LED. In exemplary embodiments, the thickness increases
approximately linearly along the length of the light guide. In
further embodiments, the thickness can increase in a non-linear
manner, and/or can achieve a maximum thickness before reaching the
far end of the light guide 1408. It should be noted that the
schematic shown in FIG. 14B showing the thickness of region 1404'
increasing linearly both along the top and bottom of the region is
for illustrative purposes only and any appropriate
shape/orientation of region 1404' can be utilized. Varying the
thickness of the region provides more uniform light illumination
from the light guide.
[0149] FIGS. 15A-15C show the intensity of light emitted from the
light guide shown in FIG. 14A. The intensity is shown as a function
of relative distance along the light guide, beginning at zero (0),
adjacent the LED (1406), to one (1), the far end of the light guide
away form the LED (1408). FIG. 15A shows the intensity of blue
light that is both emitted from the LED (going forward) and
reflected within the light guide prior to being emitted. FIG. 15B
shows the intensity of green and red light emitted from the
nanocrystals resulting from both blue light that is absorbed
directly from the LED (going forward) as well as blue light that is
reflected. Finally, FIG. 15C illustrates a plot of intensity
showing the combined sum of all blue light emitted from the light
guide (sum of blue), as well as the combined sum of all green and
red light (sum of green/red). As demonstrated in FIG. 15C, the
intensity of both the blue light and the green/red light diminishes
along the length of the light guide. The blue light diminishes as a
result of absorbance throughout the length of the light guide. As
the amount of nanocrystals in the region of the light guide are
constant (due to a uniform thickness of the region), the intensity
of the red and green light also reduce along the length of the
light guide.
[0150] FIGS. 16A-16C show intensity plots similar to those in FIGS.
15A-15C, but for the light guide configuration illustrated in FIG.
14B (region 1404' with nanocrystals that has a varying thickness).
The amount of blue light emitted both going forward and reflected
are similar to the constant thickness region. However, in comparing
the intensity of green/red light in FIGS. 16B-16C to 15B-15C, it
can be seen that a better uniformity of green/red light is emitted
from the light guide having the region with varying thickness
(1404'). This is most likely a result of the increased thickness of
region 1404' at the end of the light guide away from the LED. As
there are more nanocrystals present at the far end of the light
guide (even though the concentration may be consistent throughout
the light guide), more blue light can be absorbed and
down-converted into green and red light.
[0151] The present invention also provides display systems
comprising a display, a plurality of LEDs and a light guide
optically coupled the LEDs, wherein the display at least partially
encloses the light guide. As described herein, a plurality of
luminescent nanocrystals are dispersed in a region within the light
guide, the region extending along a length of the light guide.
Light from the LED is down-converted by the nanocrystals, exits the
light guide, and is displayed on the display. In embodiments, the
LED is a UV light emitting LED and the nanocrystals emit red, green
and blue light.
[0152] In other embodiments, a first portion of light emitted from
the LED is down-converted by the luminescent nanocrystals, and a
second portion of light emitted from the LED and the down-converted
light from the luminescent nanocrystals are emitted from the light
guide and displayed on the display. As described herein, in
exemplary embodiments the LED emits blue light, and the first
portion of blue light emitted from the LED is down-converted by the
luminescent nanocrystals to green light and red light. Suitably,
the second portion of blue light, the green light and the red light
combine to produce white light.
[0153] Exemplary nanocrystals, including core shell nanocrystals,
are described herein. In exemplary embodiments the light guide
comprises one or more reflectors.
[0154] Suitably, the region comprising the luminescent nanocrystals
is a layer of nanocrystals. In exemplary embodiments, the thickness
of the region varies along the length of the light guide, suitably
increasing from the LED along the length of the light guide, for
example, linearly, as described herein.
EXAMPLES
[0155] The following examples are illustrative, but not limiting,
of the method and compositions of the present invention. Other
suitable modifications and adaptations of the variety of conditions
and parameters normally encountered in nanocrystal synthesis, and
which would become apparent to those skilled in the art, and are
within the spirit and scope of the invention.
Example 1
Preparation of Hermetically Sealed Containers
[0156] A rectangular tube of approximate dimensions 3 mm.times.0.5
mm with a 2 mm.times.0.5 mm cavity is prepared by extrusion of
PMMA. The length of tubing is then filled with a solution
comprising fluorescent luminescent nanocrystals. The luminescent
nanocrystal solution is then cured. Segments of the tubing are then
heat sealed to trap the nanocrystals in the tubing. Suitably the
filling and sealing are performed in an inert atmosphere. A barrier
layer (e.g., SiO.sub.2, TiO.sub.2 or AlO.sub.2) can then be
disposed on the outer surface of the tubing.
[0157] A drawn glass capillary can also be used to prepare a
hermetically sealed container comprising nanocrystals. The end of
the capillary is sealed either via melt sealing or plugging with a
solder or adhesive or similar structure. The capillary can be
filled with a solution of luminescent nanocrystals such that the
entire volume of the capillary is filled with the same nanocrystal
solution, or the capillary can be filled in stages, such that
different nanocrystals are separated along the length of the
capillary. For example, a first luminescent nanocrystal solution
can be introduced into the capillary, and then a seal placed
adjacent to the solution (for example, but melt sealing or plugging
the capillary). A second luminescent nanocrystal solution can then
be added to the capillary, and again, a seal placed adjacent to the
solution. This process can be repeated as often as required until
the desired number of individual, hermetically sealed nanocrystal
segments are created. In this manner, different compositions of
luminescent nanocrystals can be separated from each other in the
same container, thereby allowing the production of containers
comprising multiple compositions (e.g., colors) of luminescent
nanocrystals. In a similar embodiment, a multi-lumen capillary can
be used in which different compositions of luminescent nanocrystals
(e.g., those which emit different colors) can be introduced and
thus kept separate from each other, and still be hermetically
sealed from external air and moisture.
Example 2
Preparation of Nanocrystals Composite Materials
[0158] Luminescent nanocrystals (e.g., CdSe/ZnS) that emit red (630
nm) and green (530 nm) light are mixed at a 3% weight concentration
into an aminosilicone polymer. The aminosilicon polymer has a
viscosity of 350 centipoises, and comprises 5% amino groups and 95%
dimethylsiloxane. The resulting composition has an optical density
of about 0.8 and a path length of 100 .mu.m.
[0159] An epoxide cross linker is added and the material is cured
to form a rubber. The cured quantum dot composition is then placed
into a ball mill and ground into a 50 .mu.m powder.
[0160] The powder is then mixed into a two part epoxy at about 30%
loading, and the polymer is degassed. The refractive index of the
nanocrystals and the epoxy are suitably matched so as to minimize
light scattering and the resulting absorptions by the
nanocrystals.
[0161] The epoxy/nanocrystal mixture is cast onto a TEFLON.RTM.
sheet at a thickness of about 300 .mu.m. After curing, the film is
removed. The optical density of the final composite material is
about 0.8 OD.
[0162] Exemplary embodiments of the present invention have been
presented. The invention is not limited to these examples. These
examples are presented herein for purposes of illustration, and not
limitation. Alternatives (including equivalents, extensions,
variations, deviations, etc., of those described herein) will be
apparent to persons skilled in the relevant art(s) based on the
teachings contained herein. Such alternatives fall within the scope
and spirit of the invention.
[0163] All publications, patents and patent applications mentioned
in this specification are herein incorporated by reference to the
same extent as if each individual publication, patent or patent
application was specifically and individually indicated to be
incorporated by reference.
* * * * *