U.S. patent application number 14/858585 was filed with the patent office on 2016-01-14 for methods for encapsulating nanocrystals and resulting compositions.
This patent application is currently assigned to Nanosys, Inc.. The applicant listed for this patent is Nanosys, Inc.. Invention is credited to Robert S. DUBROW.
Application Number | 20160009988 14/858585 |
Document ID | / |
Family ID | 42285299 |
Filed Date | 2016-01-14 |
United States Patent
Application |
20160009988 |
Kind Code |
A1 |
DUBROW; Robert S. |
January 14, 2016 |
Methods for Encapsulating Nanocrystals and Resulting
Compositions
Abstract
The present invention provides methods for hermetically sealing
luminescent nanocrystals, as well as compositions and containers
comprising hermetically scaled luminescent nanocrystals. By
hermetically sealing the luminescent nanocrystals, enhanced
lifetime and luminescence can be achieved.
Inventors: |
DUBROW; Robert S.; (San
Carlos, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nanosys, Inc. |
Milpitas |
CA |
US |
|
|
Assignee: |
Nanosys, Inc.
Milpitas
CA
|
Family ID: |
42285299 |
Appl. No.: |
14/858585 |
Filed: |
September 18, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14194996 |
Mar 3, 2014 |
9139767 |
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14858585 |
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13684782 |
Nov 26, 2012 |
8697471 |
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14194996 |
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12318516 |
Dec 30, 2008 |
8343575 |
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13684782 |
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Current U.S.
Class: |
252/301.6S ;
427/214 |
Current CPC
Class: |
B32B 2315/08 20130101;
B32B 37/144 20130101; C23C 16/402 20130101; C23C 16/405 20130101;
C09K 11/025 20130101; C23C 14/083 20130101; C23C 16/40 20130101;
C23C 16/45555 20130101; C09K 11/565 20130101; B32B 2307/412
20130101; C09K 11/703 20130101; B32B 2457/20 20130101; C09K 11/623
20130101; C09K 11/883 20130101; C09K 11/56 20130101; C23C 14/081
20130101; Y10T 156/10 20150115; B32B 37/18 20130101; C23C 14/10
20130101; Y10T 428/24355 20150115; Y10T 428/2991 20150115; Y10T
428/24851 20150115; C09K 11/70 20130101; Y10T 428/24562 20150115;
C23C 16/403 20130101; B32B 2307/414 20130101 |
International
Class: |
C09K 11/56 20060101
C09K011/56; C23C 16/455 20060101 C23C016/455; C23C 16/40 20060101
C23C016/40 |
Claims
1. A composition comprising: luminescent core-shell nanocrystals;
an inorganic layer covering each of the luminescent core-shell
nanocrystals; and a barrier layer, disposed on the inorganic layer,
configured to hermetically seal the composition.
2. The composition of claim 1, wherein the luminescent core-shell
nanocrystals are separated from each other by the inorganic
layer.
3. The composition of claim 1, wherein the luminescent nanocrystals
are selected from the group consisting of CdSe/ZnS, CdSe/CdS, and
InP/ZnS.
4. The composition of claim 1, wherein the luminescent nanocrystals
are between about 1-10 nm in size.
5. The composition of claim 1, wherein the inorganic layer
comprises silicon.
6. The composition of claim 1, wherein the inorganic layer
comprises silica or titania.
7. The composition of claim 1, wherein the barrier layer comprises
SiO.sub.2, TiO.sub.2, or AlO.sub.2.
8. A method comprising: forming a composition comprising:
luminescent core-shell nanocrystals coated with an inorganic layer,
and an inorganic layer covering each of the luminescent core-shell
nanocrystals; and disposing a barrier layer on the inorganic layer
to hermetically seal the composition.
9. The method of claim 8, wherein the luminescent core-shell
nanocrystals are separated from each other by the inorganic
layer.
10. The method of claim 8, wherein the luminescent nanocrystals are
selected from the group consisting of CdSe/ZnS, CdSe/CdS, and
InP/ZnS.
11. The method of claim 8, wherein the luminescent nanocrystals are
between about 1-10 nm in size.
12. The method of claim 8, wherein the inorganic layer comprises
silicon.
13. The method of claim 8, wherein the inorganic layer comprises
silica or titanic.
14. The method of claim 8, wherein the barrier layer comprises
SiO.sub.2, TiO.sub.2, or AlO.sub.2.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 14/194,996, filed Mar. 3, 2014, which is a divisional of
U.S. patent application Ser. No. 13/684, 782, filed Nov. 26, 2012,
which is a divisional of U.S. patent application Ser. No.
12/318,516, filed Dec. 30, 2008, each of which are incorporated
herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to methods for hermetically
sealing luminescent nanocrystals, and hermetically sealed
nanocrystal compositions. The present invention also provides
microspheres comprising luminescent nanocrystals as well as methods
of making the microspheres.
[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 areas such as
down-conversion and filtering layers, as well as other
applications, 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.
BRIEF SUMMARY OF THE INVENTION
[0006] There exists a need therefore for methods and compositions
to hermetically seal luminescent nanocrystals, thereby allowing for
increased usage lifetime and luminescent intensity. The present
invention fulfills these needs.
[0007] The present invention provides methods and compositions for
hermetically sealing luminescent nanocrystals. The compositions
prepared according to the present invention can be applied to a
variety of applications, and the methods allow for preparation of
various shapes and configurations of hermetically sealed
nanocrystal compositions.
[0008] In one embodiment, the present invention provides methods of
hermetically sealing one or more compositions comprising a
plurality of luminescent nanocrystals. In exemplary embodiments, a
first substrate is provided, and one or more compositions
comprising a plurality of luminescent nanocrystals are disposed
onto the first substrate (for example, via screen printing). A
second substrate is disposed on the first substrate so as to cover
the compositions of luminescent nanocrystals. The first and second
substrates are then sealed.
[0009] In exemplary embodiments, the first and second substrates
are glass substrates, and suitably, the substrates have one or more
recesses formed therein. In further embodiments, the first
substrate further comprises a third substrate having one or more
recesses formed therein.
[0010] Suitably, the luminescent nanocrystals for use in the
practice of the present invention are core-shell luminescent
nanocrystals, such as CdSe/ZnS, CdSe/CdS or InP/ZnS nanocrystals,
and suitably are about 1-10 nm in size.
[0011] Suitably, the first and second substrates are sealed with a
polymeric sealant, such as an epoxy sealant. In exemplary
embodiments, the luminescent nanocrystal compositions are cured
prior to sealing. In suitable embodiments, the compositions are
separated from each other following the sealing of the first and
second substrates.
[0012] The methods of the present invention can further comprise
disposing a barrier layer on the first and second substrates, such
as an inorganic layer, for example a layer of SiO.sub.2, TiO.sub.2
or AlO.sub.2. The barrier layers are suitably disposed by atomic
layer deposition or sputtering.
[0013] In further embodiments, the methods of the present invention
comprise forming one or more recesses in and/or on the first
substrate. The one or more compositions comprising a plurality of
luminescent nanocrystals are then disposed into the recesses, and
the second substrate is disposed on the first substrate so as to
cover the compositions of luminescent nanocrystals prior to
sealing.
[0014] In exemplary embodiments, the first substrate is etched so
as to form one or more recesses. In further embodiments, a third
substrate having one or more recesses formed therein is disposed
onto the first substrate. In additional embodiments, a third
substrate is disposed onto the first substrate and one or more
recesses are etched into the third substrate. In still further
embodiments, third substrate is disposed onto the first substrate
so as to form one or more recesses on the surface of the first
substrate.
[0015] The present invention also provides hermetically sealed
compositions prepared by the various methods described
throughout.
[0016] In further embodiments, the present invention provides
microspheres. Suitably, the microspheres comprise a central region,
a first layer on an outer surface of the central region. the first
layer comprising one or more luminescent nanocrystals, and a
barrier layer on an outer surface of the first layer.
[0017] Suitably, the central region of the microspheres comprises
silica, and the first layer comprises an inorganic material, such
as silica or titania. Exemplary luminescent nanocrystals, including
core-shell nanocrystals, are described throughout. Suitably, the
barrier layer comprises an inorganic layer, such as SiO.sub.2,
TiO.sub.2 or AlO.sub.2.
[0018] In exemplary embodiments, the microspheres have a diameter
of less than about 500 microns, suitably less than about 10
microns, more suitably less than about 1 micron.
[0019] The present invention also provides method of forming
microspheres. Suitably, a particle comprising a first inorganic
material is provided, and the particle is contacted with a
composition comprising a precursor to a second inorganic material
and one or more luminescent nanocrystals. A peripheral region is
formed on an outer surface of the particle, the peripheral region
comprising the second inorganic material and the luminescent
nanocrystals. Then, a barrier layer is disposed on an outer surface
of the peripheral region.
[0020] 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.
[0021] 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
[0022] 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.
[0023] FIGS. 1A-1D show a method of hermetically sealing
luminescent nanocrystals in accordance with an embodiment of the
present invention.
[0024] FIG. 1E shows a flowchart of a method of hermetically
sealing luminescent nanocrystals in accordance with an embodiment
of the present invention.
[0025] FIGS. 2A-2G show a method of hermetically sealing
luminescent nanocrystals in accordance with an embodiment of the
present invention.
[0026] FIGS. 3A-3C show separating hermetically sealed luminescent
nanocrystals in accordance with an embodiment of the present
invention.
[0027] FIG. 4 shows a flowchart of a method of hermetically sealing
luminescent nanocrystals in accordance with an embodiment of the
present invention.
[0028] FIG. 5 shows a microsphere in accordance with an embodiment
of the present invention.
[0029] FIG. 6 shows a flowchart of a method of preparing a
microsphere in accordance with an embodiment of the present
invention.
[0030] 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
[0031] 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.
[0032] 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.
[0033] Typically, the region of characteristic dimension will he
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.
[0034] 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 Published U.S. patent application No.
2008/0237540; U.S. Pat. No.7,374,807; 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.
[0035] 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.
[0036] 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. Pat.
No. 7,374,807 U.S. Pat. No. 6,949,206 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.
[0037] 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.
[0038] Down-converting nanocomposites (for example, as disclosed in
U.S. Pat. No. 7,374,807) 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.
Luminescent Nanocrystal Phosphors
[0039] 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.
[0040] 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.
[0041] 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
[0042] 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.
[0043] 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. Additionally, the spherical shape acts
to minimize interfacial strain energy from the large radius of
curvature, thereby preventing the formation of dislocations that
could degrade the optical properties of the nanocrystal system.
[0044] 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, Sc, 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
[0045] In one embodiment, the present invention provides methods of
hermetically sealing one or more compositions comprising a
plurality of luminescent nanocrystals. As shown in flowchart 120 of
FIG. 1E, with reference to the schematics in FIGS. 1A-1D, suitably
the methods comprise providing a first substrate 102 in step 122.
In step 124, one or more compositions 104 comprising a plurality of
luminescent nanocrystals 106 are disposed onto the first substrate
102. In step 126, a second substrate 108 is disposed on the first
substrate so as to cover the compositions 104 of luminescent
nanocrystals 106 as in FIG. 1B. In step 128, the first and second
substrates are then sealed.
[0046] As discussed throughout, the terms "hermetic," "hermetic
sealing," and "hermetically sealed" are used to indicate that the
compositions of 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).
[0047] 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.
[0048] Suitable matrixes for use in the compositions of the present
invention include polymers and organic or 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 is substantially translucent, transparent, or substantially
transparent. Such polymers include, but are not limited to,
poly(vinylbutyral):poly(vinylacetate); 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 laurylrnethacrylate;
styrene based polymers; and polymers that are crosslinked with
difunctional monomers, such as divinylbenzene.
[0049] 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.
[0050] In exemplary embodiments, first substrate 102 and second
substrate 108 are transparent, substantially transparent, or
translucent substrate, such a polymer or a glass (e.g., a
silica-comprising glass). In exemplary embodiments, both first and
second substrate comprise glass. though in other embodiments, one
of the substrates can be glass and the other a polymeric material,
or both can be polymeric materials. As shown in FIG. 1A, suitably
first substrate 102 is of a size such that more than one
composition 104 of luminescent nanocrystals 106 can be disposed
thereon. However, in additional embodiments, a single composition
104 comprising a plurality of luminescent nanocrystals 106 be
disposed on a first substrate, and if desired, a plurality of first
substrates can then be used to prepare multiple hermetically sealed
compositions. The thickness of first substrate 102 is suitably on
the order of about 1 .mu.m to about 1 cm, suitably about 100 .mu.m
to about 100 mm. First and second substrates are suitably the same
size, though in other embodiments, they can be different sizes, so
long as the compositions are sealed by the substrates. Suitably,
first and second substrates are on the order of millimeters to
meters in at least one lateral dimension (i.e., in the plane of the
substrate). Providing a first substrate 102 that is transparent,
translucent or semi-transparent, allows light to pass through
substrate and contact the luminescent nanocrystals disposed
thereon.
[0051] The thickness and size (e.g., area of coverage) of the
compositions 104 of the present invention that are disposed on the
first substrate 102 can be controlled by any method known in the
art, such as spin-coating, screen printing, dip-coating, painting,
spraying, etc. The luminescent nanocrystal compositions of the
present invention can be any desirable size, shape, configuration
and thickness. For example, the compositions can be disposed on the
first substrate in the form of layers. as well as other shapes, for
example, discs, drops, spheres, cubes or blocks, tubular
configurations and the like. While the various compositions of the
present invention can be any required or desired thickness,
suitably, the compositions are on the order of about 1 .mu.m to
about 500 .mu.m in thickness (i.e., in one dimension). Suitably,
the compositions have at least one lateral dimension (i.e., in the
plane of the substrate) that is in the range of about a few microns
to centimeters. The luminescent nanocrystals can be embedded or
dispersed in the various compositions/matrixes at any loading ratio
that is appropriate for the desired function. Suitably, the
luminescent nanocrystals are 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 compositions are on the order
of about 10% by volume, to parts-per-million (ppm) levels.
[0052] 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.
[0053] 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.
[0054] While luminescent nanocrystals of any suitable material can
be used in the practice of the present invention, in certain
embodiments, the nanocrystals are ZnS, InAs or CdSe nanocrystals,
or the nanocrystals 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.
[0055] As discussed throughout, the compositions 104 of luminescent
nanocrystals 106 suitably comprise a polymeric substrate or matrix.
Thus, the present invention comprises methods of hermetically
sealing compositions comprising luminescent nanocrystals, suitably
polymeric substrates comprising luminescent nanocrystals, by
sealing the compositions between a first and second substrates.
[0056] The ability to use polymeric substrates in the compositions
104 allows for the formation of various shapes and configurations
of the compositions, simply by molding, spreading, dropping,
dispensing, spraying, layering, 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, or can simply be disposed in a 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, as shown in
FIG. 1A, the compositions can be disposed in the shapes of disks or
droplets.
[0057] In exemplary embodiments, the compositions 104 comprising
luminescent nanocrystals 106 (note, figures are not to scale) are
disposed on substrate 102 in a high-throughput format, for example,
by using screen printing, ink-jet printing, or other application
technique that deposit a large number of individual samples onto a
substrate.
[0058] In suitable embodiments, the sealing in step 128 of
flowchart 120 comprises sealing with a polymeric sealant. Suitable
polymeric sealants that can be used in the practice of the present
invention are well known in the art, and are those which when dried
or cured, are transparent, or at least semitransparent, or
translucent. Exemplary polymeric sealants which can be utilized
include, but are not limited to, silicones, epoxies, various
rubbers, various acrylics, etc. In addition to suitably being
transparent or at least translucent, the sealant should also be
impermeable, or at least substantially impermeable, to air and
moisture, so as to hermetically seal the first and second
substrates.
[0059] Suitably, the first 102 and second 108 substrates are sealed
by introducing sealant 110 to the first and second substrates. for
example, by pouring, dipping, wicking, painting, injecting, etc.,
sealant 110, such that the sealant forms a seal 112 between the
first and second substrates. Suitably, the luminescent nanocrystal
composition is cured (e.g., via heating or cooling) prior to the
sealing with the sealant.
[0060] In further embodiments, as shown in FIGS. 2A-2B first
substrate 102 suitably comprises one or more recesses 202 formed,
at least one of, in and on, the substrate. As used herein, a
"recess" refers to a hole, indentation, well, crack, imperfection,
or other depression in and/or on substrate 102. Forming the
recesses, at least one of, in and on, means that the recesses are
formed in and/or on, the substrate 102. A recess "on" first
substrate 102 refers to a recess that is above the surface of first
substrate 102, for example, a recess formed in a third substrate as
described herein. A recess that is "in" first substrate 102 refers
to a recess that penetrates into the surface of first substrate 102
to any depth. Note that recesses can be formed both in and on the
substrate in the same composition, or can be formed only in, or
only on, the substrate 102.
[0061] Suitably, recesses in substrate 102 will not pass through
the entire substrate, but instead have a depth into the substrate
that is less than the entire thickness of the substrate, thereby
providing a reservoir for receipt of compositions 104. Suitably,
the recesses 202 are on the order of about 0.5 mm to about 10 mm in
at least one lateral dimension (a dimension in the plane of first
substrate 102, e.g., diameter if a circular-shaped recess is
utilized), more suitably about 1 mm to about 10 mm, about 1 mm to
about 9 mm, about 1 mm to about 8 mm, about 1 mm to about 7 mm,
about 1 mm to about 6 mm, about 1 mm to about 5 mm, about 1 mm to
about 4 mm, about 1 mm to about 3 mm, about 1 mm to about 2 mm, or
about 10 mm, about 9 mm, about 8 mm, about 7 mm, about 6 mm, about
5 mm, about 4 mm, about 3 mm, about 2 mm, or about 1 mm, in at
least one lateral dimension.
[0062] Recesses will suitably be separated by sections of substrate
102 (or other materials as described herein) so that they are on
the order of about 0.1 mm to about 10 mm apart (edge-to-edge
separation). Suitably, recesses 202 are separated by distances of
about 1 mm to about 10 mm, about 1 mm to about 9 mm, about 1 mm to
about 8 mm, about 1 mm to about 7 mm, about 1 mm to about 6 mm,
about 1 mm to about 5 mm, about 1 mm to about 4 mm, about 1 mm to
about 3 mm. about 1 mm to about 2 mm, or about 10 mm, about 9 mm,
about 8 mm, about 7 mm, about 6 mm, about 5 mm, about 4 mm, about 3
mm, about 2 mm, or about 1 mm.
[0063] The depth of recesses 202 into the surface of substrate 102
(i.e., the distance into the substrate normal to the surface of the
substrate) is partially dictated by the thickness of substrate 102,
though the depth suitably extends only a portion of the way into
the surface of substrate 102. In exemplary embodiments, the depth
of recesses 202 is on the order of about 100 .mu.m to about 100 mm,
suitably about 500 .mu.m to about 10 mm. While in exemplary
embodiments the depth of recesses 202 can be uniform across the
recess, in other embodiments, the recess can have a sloping or
non-inform depth.
[0064] While in exemplary embodiments, recesses 202 have a circular
cross-section, in other embodiments, any shape can be used, e.g.,
rectangular, square. triangular, irregular, etc.
[0065] As shown in a further embodiment in FIG. 2F, first substrate
102 can further comprise a third substrate 204 that has one or more
recesses 202 formed into the third substrate 204. Suitably, the
recesses in the third substrate will pass all the way through to
the surface of first substrate 102 (in suitable embodiments,
surface 102 may also have recesses therein), though in other
embodiments, recesses 202 in third substrate 204 will not pass all
the way through the third surface. Thus, as shown in FIG. 2F,
recesses 204 can be in the form of cylinders (or other suitable
shapes, e.g., rectangles, squares, irregular shapes, etc.). The
thickness of third substrate is suitably on the order of about 100
.mu.m to about 100 mm, suitably about 500 .mu.m to about 10 mm, or
about 500 .mu.m to about 5 mm.
[0066] In exemplary embodiments, third substrate 204 comprises a
polymeric material, including a photoresistant materials. The use
of a photoresistant material allows for masking and etching to
produce recesses 202 in the third substrate 204 (as described
herein). Examples of methods of the use of photoresistant
materials, as well as photoresist developers, can be found in, for
example, Sze, S. M., "Semiconductor Devices, Physics and
Technology," John Wiley & Sons, New York, pp. 436-442 (1985).
the disclosure of which is incorporated by reference herein in its
entirety. In general, photoresists (such as negative photoresists)
for use in the practice of the present invention comprise a polymer
combined with a photosensitive compound. Upon exposure to radiation
(e.g., UV light), the photosensitive compound cross-links the
polymer, rendering it resistant to a developing solvent. Unexposed
areas, however, are removable by the developing solvent. Some
exemplary negative photoresist materials and developers include
Kodak.RTM. 747, copolymer-ethyl acrylate and glycidylmethacrylate
(COP), GeSe and poly(glycidylmethacrylate-co-ethylacrylate) DCOPA.
Disposing of negative photoresist material can be performed using
any suitable method, for example, spin coating, spray coating, or
otherwise layering the material. In contrast. "positive
photoresistant" materials become less chemically robust when
exposed to radiation, and hence, work in the opposite manner to
negative photoresistant materials. Here, materials that are exposed
to radiation will remain to generate the mask, while unexposed
areas will be removed.
[0067] As shown in FIGS. 2B and 2C, compositions 104 comprising
luminescent nanocrystals are disposed in the recesses 202.
Suitably, the recesses are filled such that there is no, or very
little, gap between the top of the composition 104 and the surface
of the substrate 102. This provides for a tight seal between the
second substrate 108 and the first substrate 102, as shown in FIG.
2C-2E, when sealed with sealant 110, thereby providing hermetically
sealed luminescent nanocrystals. When a third substrate 204
comprising recesses 202 is utilized, suitably the compositions 104
are disposed in the recesses so that there is no, or very little,
gap between the top of the composition and the surface of the third
substrate 204.
[0068] In further embodiments, as shown FIG. 1E, the methods of the
present invention can further comprise step 130, in which a barrier
layer (not shown) is disposed on the surface of the first 102 and
second substrates 108. As used herein, the term "barrier layer" is
used to indicate a layer, coating, sealant or other material that
is disposed on the first and second substrates. Such barrier layers
provide an additional measure of hermetic sealing above and beyond
the hermetic sealing provided by sealing of the first and second
substrates.
[0069] Examples of barrier layers include any material layer,
coating or substance that can create an airtight seal on the
substrates/compositions. 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 suitable 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 substrates/compositions. In
suitable embodiments, sputtering is used to dispose the barrier
layer on the substrates/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.
[0070] In further embodiments, disposing the barrier layer can be
carried out using atomic layer deposition. 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, substrates and/or the nanocrystals. Therefore, in
suitable embodiments, atomic layer deposition is used to dispose
the barrier layer.
[0071] 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
substrates/compositions, 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.
[0072] 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 substrates/compositions. 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
substrates/compositions on which the reaction gas A has been
adsorbed, resulting in an atomic barrier layer on the
substrates/compositions.
[0073] 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.
[0074] Use of ALD for disposition of a barrier layer on the
substrates/compositions 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 layer.
[0075] Suitably, the ALI) 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.
[0076] 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.
[0077] As shown in flowchart 120 of FIG. 1E, the methods of the
present invention suitably further comprise separating the one or
more hermetically sealed compositions from each other following
sealing of the substrate layers, as shown in FIGS. 3A-3C. This
separation can be before or after the disposing of a barrier layer,
though suitably the barrier layer, if utilized, is disposed after
the separation.
[0078] As shown in FIGS. 3A-3C, a hermetically sealed structure 302
comprising multiple, individually sealed compositions can be
separated into sub-structures 304, or suitably further into
individual structures 306, each comprising a single hermetically
sealed composition, which in itself comprises a plurality of
luminescent nanocrystals. Thus, preparation of a plurality of
sealed compositions can lead to individual, separated
compositions.
[0079] Methods for separating the hermetically sealed compositions
from each other include various methods well known in the art, such
as via mechanical dicing (e.g., via knife, wedge, saw, blade, or
other cutting device), via a laser, via water jet, etc.
[0080] In further embodiments, the present invention provides
additional methods of hermetically sealing one or more compositions
of luminescent nanocrystals. As shown in flowchart 400 of FIG. 4,
with reference to FIGS. 2A-2G, in exemplary embodiments, the
methods comprise step 402, in which a first substrate 102 is
provided. In step 404 of flowchart 400, one or more recesses 202
are generated in and/or on the first substrate.
[0081] In step 406 of flowchart 400, one or more compositions 104
comprising a plurality of luminescent nanocrystals 106 are disposed
into the recesses 204. In step 408, a second substrate 108 is then
disposed on the first substrate 102 so as to cover the compositions
104 of luminescent nanocrystals 106. In step 410 of flowchart 400,
the first and second substrates are then sealed 112.
[0082] As described throughout, suitably substrates 102 and 108 are
transparent, semi-transparent or translucent substrates, such as
polymer or glass substrates. The size and thickness of substrates
102 and 108 are described throughout.
[0083] Step 404 of flowchart 400 comprises generating one or more
recesses 202 in and/or on the first substrate 102. In exemplary
embodiments, recesses 202 are generated directly in the surface of
first substrate 102. That is, material is removed from the surface
of first substrate 102 so as to generate recesses 202. Methods for
removing material from first substrate 102 include etching (e.g.,
chemical etching using various acids or other etchants, including
those disclosed herein), gouging, cutting, whittling, drilling,
etc.
[0084] In further embodiments, recesses 202 can be generated on
first substrate 102. In such embodiments, a third substrate 204 is
suitably disposed on first substrate 102. Recesses 202 are then
generated in the third substrate, for example, by etching (e.g.,
chemical etching using various acids), gouging, cutting, whittling,
drilling, etc., into the substrate. Suitably. a masking/etching
method is used to generate recesses in the third substrate. In
further embodiments, recesses 202 can be generated by disposing a
previously prepared third substrate in which recess have already
been generated. In still further embodiments, recesses can be
formed on the surface of first substrate 102 by disposing and
arranging third substrate sections 206 on first substrate 102,
wherein recesses 202 are generated or formed within the gaps/spaces
between the sections, as shown in FIG. 2G.
[0085] Exemplary compositions comprising luminescent nanocrystals
(e.g., polymeric compositions/matrixes) as well as suitable
nanocrystals are described throughout. Suitably, the luminescent
nanocrystals are core-shell luminescent nanocrystals, such as
CdSe/ZnS, CdSe/CdS and InP/ZnS. Exemplary sizes of nanocrystals are
described herein, and suitably, the luminescent nanocrystals are
between about 1-10 nm in size. Methods for disposing the
compositions of luminescent nanocrystals in the recesses are
described throughout, and include screen printing and other methods
to generate a high-throughput deposition.
[0086] As described throughout, suitably second substrate is a
transparent, semi-transparent or translucent substrate, such as a
polymeric material or a glass. Hermetically sealing the
compositions of luminescent nanocrystals between two glass
substrates allows the nanocrystals to be utilized in various
applications, such as in down-conversion in LEDs, as described
herein.
[0087] As described throughout, suitably the first and second
substrates are sealed with a polymeric sealant, such as a
silicon-based, epoxy-based or acrylic-based sealant. The sealant
can he introduced 110 to the first and second substrates using any
suitable method, such as pouring the sealant over the substrates
(and then squeezing out residual by applying pressure to the
substrates), wicking the substrate into space between the
substrates, injecting the sealant, dipping the substrates in a
sealant, and other suitable methods. In other embodiments, a
sealant can simply be disposed on the outside edges of the first
and second substrates, for example, by painting, spraying,
spreading or otherwise applying the sealant without requiring the
sealant to penetrate between the first and second substrates.
[0088] As shown in FIG. 4, suitably, the luminescent nanocrystals
are cured in step 412 prior to sealing the first and second
substrates in step 410, though in additional embodiments, the
substrates can be sealed and then the compositions of luminescent
nanocrystals can be cured.
[0089] The methods of the present invention can also further
comprise step 414 of flowchart 400, of disposing a barrier layer on
the first and second substrates to further hermetically seal the
substrates. Methods of disposing a barrier layer (e.g., atomic
layer deposition, sputtering, etc.) are described throughout, as
are exemplary barrier layers, including inorganic layers, such as
layers comprising SiO.sub.2, TiO.sub.2 or AlO.sub.2.
[0090] As shown in flowchart 400, the methods suitably further
comprise step 416, in which the hermetically sealed compositions
are separated from each other, as shown in FIGS. 3A-3C, for
example. The separation can occur before of after the barrier layer
is disposed. As described herein, the methods provided allow for a
high-throughput generation individual, separate samples of
luminescent nanocrystals that can be used in various applications,
such as in LEDs, displays, etc.
[0091] The present invention also provides hermetically sealed
compositions prepared by the various methods described herein.
Exemplary compositions, sizes and characteristics of the
luminescent nanocrystals, as well as the substrates, sealants and
other components (e.g., barrier layers) of the sealed compositions
are described throughout.
[0092] In suitable embodiments of the present invention, the
various steps to produce a hermetically sealed compositions of
luminescent nanocrystals are performed in an inert atmosphere,
i.e., either in a vacuum and/or with only N.sub.2 or other inert
gas(es) present.
[0093] 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. No. 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.
[0094] In additional embodiments, the hermetically sealed
compositions 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 is less than about 1/5 the
thickness of the LED layer. For example, the luminescent
nanocrystal composition or container is 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.
[0095] In still further embodiments, the present invention provides
microspheres 500, as shown in FIG. 5. Suitably, the microspheres of
the present invention comprise a central region 502 and a first
layer 504 on an outer surface 506 of central region 502, first
layer 504 comprising one or more luminescent nanocrystals 508. The
microspheres 500 further comprise a barrier layer 512 on an outer
surface 510 of first layer 504.
[0096] Exemplary microspheres comprising a central region, a first
layer, and nanoparticles, as well as methods of producing such
microspheres, are disclosed in U.S. Pat. No. 7,229,690, the
disclosure of which is incorporated by reference herein in its
entirety.
[0097] As disclosed in U.S. Pat. No. 7,229,690, suitably central
region 502 comprises silica, and first layer 504 comprises an
inorganic material, such as silica or titania. Luminescent
nanocrystals 508 for inclusion in the microspheres are disclosed
herein, and suitably comprise core-shell luminescent nanocrystals,
such as CdSe/ZnS, CdSe/CdS or InP/ZnS nanocrystals. In exemplary
embodiments, the luminescent nanocrystals are between about 1-10 nm
in size.
[0098] As described in detail herein, the addition of a barrier
layer to the surface of a composition comprising luminescent
nanocrystals provides a hermetic seal on the composition, thus
reducing or eliminating the passage of moisture and/or air to the
nanocrystals. Suitably, barrier layer 512 on microspheres 500
comprises an inorganic layer SiO.sub.2, TiO.sub.2 or AlO.sub.2,
though other layers as described herein and known in the art can
also be utilized.
[0099] In exemplary embodiments, the microspheres 500 of the
present invention have a diameter of less than about 500 microns,
for example, less than about 400 microns, less than about 250
microns. less than about 100 microns, less than about 50 microns,
less than about 10 microns, or less than about 1 micron, including
values between these ranges.
[0100] The present invention also provides methods of forming
microspheres, as shown in flowchart 600 of FIG. 6, with reference
to FIG. 5. In step 602 of flowchart 600, a particle 502 comprising
a first inorganic material is provided. The particle is then
contacted with a composition comprising a precursor to a second
inorganic material and one or more luminescent nanocrystals 508, in
step 604. In step 606, a peripheral region 504 is formed on an
outer surface 506 of the particle 502, the peripheral region
comprising the second inorganic material and the luminescent
nanocrystals 508. Then, in step 608, a barrier layer 512 is
disposed on an outer surface 510 of the peripheral region 504.
[0101] As noted herein, suitably a silica particle is provided, and
the particle is contacted with an organic material comprising
silica or titanic which comprises the luminescent nanocrystals. As
described herein, the luminescent nanocrystals are suitably
core-shell luminescent nanocrystals, such as CdSe/ZnS, CdSe/CdS or
InP/ZnS nanocrystals with a size of about 1-10 nm. Methods for
preparing silica particles and peripheral regions 504 are described
throughout U.S. Pat. No. 7,229,690.
[0102] Suitably, a barrier layer comprising an inorganic layer,
such as SiO.sub.2, TiO.sub.2 or AlO.sub.2 is disposed on the
microspheres. As described herein, the barrier layers can be
disposed in various ways. including atomic layer deposition and
sputtering.
[0103] 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.
[0104] 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.
* * * * *