U.S. patent application number 14/515814 was filed with the patent office on 2015-04-23 for light emitting diode (led) devices.
The applicant listed for this patent is NANOSYS, INC.. Invention is credited to Jian CHEN, Robert S. Dubrow, Steven Gensler, Jason Hartlove, Ernest Lee, Robert Edward Wilson.
Application Number | 20150109814 14/515814 |
Document ID | / |
Family ID | 52826010 |
Filed Date | 2015-04-23 |
United States Patent
Application |
20150109814 |
Kind Code |
A1 |
CHEN; Jian ; et al. |
April 23, 2015 |
LIGHT EMITTING DIODE (LED) DEVICES
Abstract
Disclosed teem are display systems comprising light-emitting,
diodes (LEDs), suitably blue light LEDs, which demonstrate
increased optical power output. In embodiments, the display systems
include compositions comprising phosphors, including luminescent
nanocrystals.
Inventors: |
CHEN; Jian; (Saratoga,
CA) ; Dubrow; Robert S.; (San Carlos, CA) ;
Gensler; Steven; (San Jose, CA) ; Hartlove;
Jason; (Los Altos, CA) ; Lee; Ernest; (Palo
Alto, CA) ; Wilson; Robert Edward; (Palo Alto,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NANOSYS, INC. |
Milpitas |
CA |
US |
|
|
Family ID: |
52826010 |
Appl. No.: |
14/515814 |
Filed: |
October 16, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61892027 |
Oct 17, 2013 |
|
|
|
Current U.S.
Class: |
362/606 |
Current CPC
Class: |
G02B 6/005 20130101;
G02F 2001/133614 20130101; G02F 1/133615 20130101; G02B 6/0073
20130101; H01L 33/502 20130101 |
Class at
Publication: |
362/606 |
International
Class: |
F21V 8/00 20060101
F21V008/00; F21K 2/00 20060101 F21K002/00 |
Claims
1. A display system, comprising: a) one or more blue light emitting
diode(s) (LED); b) a light guide plate, optically coupled to the
blue LED; c) a display; and d) a composition comprising a plurality
of phosphors, the composition oriented between the light guide
plate and the display, wherein the display system exhibits
increased optical power output as compared to a display system
where the light guide plate is not optically coupled to the blue
LED.
2. The display system of claim 1, wherein the light guide plate is
optically coupled to the blue LED with, a tape or an adhesive.
3. The display system of claim 1, wherein the light guide plate is
optically coupled to the blue LED via an ecapsulant protruding from
the LED.
4. The display system of claim 1, wherein, the phosphors are YAG
phosphors, silicate phosphors, garnet phosphors, aluminate
phosphors, nitride phosphors, NYAG phosphors, SiAlON phosphors and
CASN phosphors.
5. The display system of claim 1, wherein the phosphors are
luminescent nanocrystals.
6. The display system of claim 5, wherein the luminescent
nanocrystals comprise CdSe or ZnS.
7. The display system of claim 5, wherein the luminescent
nanocrystals comprise CdSe/ZnS, InP/ZnS, InP/ZnSe, PbSe/PbS,
CdSe/CdS, CdTe/CdS or CdTe/ZnS.
8. The displays system of claim 1, wherein the composition is a
film.
9. The display system of claim 1, wherein the display is a liquid
crystal module.
10. The display system of claim 1, wherein the system further
comprises one or more of a diffuser, one or more brightness
enhancement films (BEFs) and a reflector.
11. The display system of claim 1, wherein the display system
exhibits at least a 10% increase in optical power output as
compared to a display system where the light guide plate is not
optically coupled to the blue LED.
12. A display system, comprising: a) one or more blue light
emitting diode(s) (LED); b) a light guide plate, optically coupled
to the blue LED; c) a display; and d) a film comprising a plurality
of phosphors, the composition oriented between the light guide
plate and die display, wherein the display system exhibits at least
a 10% increase In optical power output as compared to a display
system where the light guide, plate is not optically coupled to the
blue LED.
13. The display system of claim 12, wherein the light guide plate
is optically coupled to the blue LED with a tape or an
adhesive.
14. The display system of claim 12, wherein the light guide plate
is optically coupled to the blue LED via an encapsulant protruding
from the LED.
15. The display system of claim 12, wherein the phosphors are YAG
phosphors, silicate phosphors, garnet phosphors, aluminate
phosphors, nitride phosphors, NYAG phosphors, SiAlON phosphors and
CASN phosphors.
16. The display system of claim 12, wherein the phosphors are
luminescent nanocrystals.
17. The display system of claim 16, wherein the luminescent
nanocrystals comprise CdSe or ZnS.
18. The display system of claim 16, wherein the luminescent
nanocrystals comprise CdSe/ZnS, InP/ZnS, InP/ZnSe, PbSe/PbS,
CdSe/CdS, CdTe/CdS or CdTe/ZnS.
19. The displays system of claim 12, wherein the film is a
polymeric film.
20. The display system of claim 12, wherein the display is a liquid
crystal module.
21. The display system of claim 12, wherein the system further
comprises one or more of a diffuser, one or more brightness
enhancement films (BEFs) and a reflector.
22. A display system, comprising: a) one or more blue light
emitting diode(s) (LED); b) a light guide plate, optically coupled
to the blue LED; c) a polymeric film comprising a plurality of
phosphors, the polymeric film oriented above the light guide plate;
d) one or more brightness enhancement films (BEFs) oriented above
the polymeric film; e) a top diffuser oriented above the BEFs; and
f) a liquid crystal module oriented above the top diffuser, wherein
the display system exhibits at least a 10% increase in optical
power output as compared to a display system where the light guide
plate is not optically coupled to the blue LED.
23. The display system of claim 22, wherein the light pride plate
is optically coupled to the blue LED with a tape or an
adhesive.
24. The display system of claim 22, wherein the light guide plate
is optically coupled, to the blue LED via an encapsulant protruding
from the LED.
25. The display system of claim 22, wherein the phosphors are YAG
phosphors, silicate phosphors, garnet phosphors, aluminate
phosphors, nitride phosphors, NYAG phosphors, SiAlGN phosphors and
CASN phosphors.
26. The display system of claim 22, wherein the phosphors are
luminescent nanocrystals.
27. The display system of claim 26, wherein the luminescent
nanocrystals comprise CdSe or ZnS.
28. The display system of claim 26, wherein the luminescent
nanocrystals comprise CdSe/ZnS, InP/ZnS, InP/ZnSe, PbSe/PbS,
CdSe/CdS, CdTe/CdS or CdTe/ZnS.
29. The display system of claim 22, wherein the system further
comprises a reflector oriented below the light guide plate.
30. A method of increasing the optical power output of a blue LED
in a display system, comprising optically coupling the blue LED to
a light guide plate of the display system.
31. The method of claim 30, wherein the optical coupling comprises
coupling the blue LED to the light guide plate with tape or an
adhesive.
32. The method of claim 30, wherein the light guide plate is
optically coupled to the blue LED via an encapsulant protruding
from the LED.
33. The method of claim 30, wherein the method Increases the
optical power output of the blue LED by at least 10% as compared to
a display system that does not comprise the blue LED optically
coupled to the light guide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention claims the benefit of U.S. Provisional
Patent Application No. 61/892,027, filed Oct. 17, 2013, the
disclosure of which is incorporated by reference herein in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to display systems comprising
light-emitting diodes (LEDs), suitably blue light LEDs, which
demonstrate increased optical power output. In embodiments, the
display systems include compositions comprising phosphors,
including luminescent nanocrystals.
[0004] 2. Background of the Invention
[0005] In liquid crystal display (LCD) backlights, white LEDs are
typically
[0006] utilized as a light source. In one configuration, the LEDs
are arranged around the edge or perimeter of the display. In such
the case of edge-lit backlights, light emanating from the LEDs
enters a light guide, plate which distributes white light uniformly
across the display. White LED package designs have been optimized
to enable high extraction efficiency and coupling efficiency into
the light guide plate.
[0007] LCD backlights often utilize phosphors, such as YAG
phosphors. Traditionally, these phosphors have been situated inside
the LED package itself. Luminescent nanocrystals represent a new,
alternative class of phosphors often, used in remote-phosphor
configurations where the phosphor is no longer inside the LED
package. For example, luminescent nanocrystals can be embedded in a
flexible film/sheet that is placed above a light guide plate (sec.
e.g., Published U.S. Patent Application Nos. 2010/0110728 and
2012/0113672, the disclosures of each of which are incorporated by
reference herein m their entireties). In other examples,
luminescent nanocrystals are encapsulated in a container, for
example a capillary, which is placed between the LEDs and the light
guide plate. (see, e.g., Published U.S. Patent Application No
2010/0110728).
[0008] Blue LED light extraction efficiency and coupling efficiency
into the light guide plate play a critical role in the overall
display efficiency. Blue light extraction efficiency is poor in
current blue LED designs. This is most likely a result of the
reflection from the encapsulation-polymer/air interface. A
significant amount of the blue light is reflected, from this
interface back toward the blue die of the LED, which in turn
absorbs the blue light.
[0009] Disclosed herein are embodiments that overcome this
deficiency with bins LED-based display devices, thereby increasing
the optical power output of such devices.
SUMMARY OF PREFERRED EMBODIMENTS
[0010] In embodiments, the present application provides display
systems, suitably comprising one or more blue light emitting
diode(s) (LED), a light guide plate, optically coupled to the blue
LED, a display and a composition comprising a plurality of
phosphors, the composition oriented between the light guide plate
and the display. Suitably, the display system exhibits increased
optical power output as compared to a display system where the
light guide plate is not optically coupled to the blue LED.
[0011] In embodiments, the light guide plate is optically coupled,
to the blue LED with a tape or an adhesive, in embodiments, the
light guide plate is optically coupled to the blue LED via an
encapsulant protruding from the LED.
[0012] Suitably, the phosphors are YAG phosphors, silicate
phosphors, garnet phosphors, aluminate phosphors, nitride
phosphors, NYAG phosphors, SiAlON phosphors and CASN phosphors. In
further embodiments, the phosphors are luminescent nanocrystals,
for example, luminescent nanocrystals comprising CdSe or ZnS,
including, for example, luminescent nanocrystals comprising
CdSe/ZnS, InP/ZnS, InP/ZnSe, PbSe/PbS, CdSe/CdS, CdTe/CdS or
CdTe/ZnS.
[0013] In exemplary embodiments, the composition is a film.
[0014] Suitably, the display is a liquid, crystal module.
[0015] In additional embodiments, the systems further comprise one
or more of a diffuser, one or more brightness enhancement films
(BEFs) and a reflector.
[0016] In embodiments, the display systems suitably exhibit at
least a 10% increase in optical power output as compared to a
display system where the light guide plate is not optically coupled
to the blue LED.
[0017] Also provided are display systems, suitably comprising one
or more blue light emitting diode(s) (LED) a light guide plate,
optically coupled to the blue LED a display and a film comprising a
plurality of phosphors, the composition oriented between the light
guide plate and the display. Suitably, the display system exhibits
at least a 10% increase in optical power output as compared to a
display system where the light guide plate is not optically coupled
to the blue LED.
[0018] Exemplary methods for optical coupling are described herein,
as are suitable phosphors, including luminescent nanocrystals.
[0019] Also provided are display systems, suitably comprising one
or more blue light emitting diode(s) (LED), a light guide plate,
optically coupled to the blue LED, a polymeric film comprising a
plurality of phosphors, the polymeric film oriented above the light
guide plate, one or more brightness enhancement films (BEFs)
oriented above the polymeric film, a top diffuser oriented above
the BEFs and a liquid crystal module oriented above the top
diffuser. Suitably, the display systems exhibit at least a 10%
increase in optical power output as compared to a display system
where the light guide plate is not optically coupled to the blue
LED.
[0020] Exemplary methods for optical coupling are described herein,
as are suitable phosphors, including luminescent nanocrystals.
[0021] Also provided are methods of increasing the optical power
output of a blue LED in a display system, comprising optically
coupling the blue LED to a light guide plate of the display
system.
[0022] In embodiments of the methods, the optical coupling
comprises coupling the blue LED to the light guide plate with tape
or an adhesive. In embodiments of the methods, the light guide
plate is optically coupled to the blue LED via an encapsulant
protruding from the LED.
[0023] Suitably, the methods increase the optical power output of
the blue LED by at least 10% as compared to a display system that
does not comprise the blue LED optically coupled, to the light
guide.
[0024] Further embodiments, features, and advantages of the
embodiments, as well as the structure and operation of the various
embodiments, are described in detail below with reference to
accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0025] FIG. 1A shows an exemplary display system as described
herein.
[0026] FIG. 1B shows an additional exemplary display system as
described herein.
[0027] FIGS. 2A-2C show schematics illustrating the source of loss
of optical power output in blue LEDs and the effect of optical
coupling between an LED and a light guide plate.
[0028] FIGS. 3A-3B show theoretical calculations of spectral power
density and integrated spectral power density for blue and white
LEDs.
[0029] FIGS. 4A-4C show images of backlights in three different
LED/optical coupling configurations.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0030] It should be appreciated that the particular implementations
shown and described herein are examples and are not intended to
otherwise limit the scope of the application in any way.
[0031] The published patents, patent applications, websites,
company names, and scientific literature, referred to herein are
hereby incorporated by reference in their entirety to the same
extent as if each, was specifically and individually indicated to
be incorporated by reference. Any conflict between any reference
cited herein and the specific teachings of this specification shall
be resolved in favor of the latter. Likewise, any conflict between
an art-understood definition of a word or phrase and a definition
of the word or phrase as specifically taught in this specification
shall be resolved in favor of the latter.
[0032] As used in this specification, the singular forms "a," "an"
and "the" specifically also encompass the plural forms of the terms
to which they refer, unless the content clearly dictates otherwise.
The term "about" is used herein to mean approximately, in the
region of, roughly, or around. 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 sixes from 90 nm to 110 nm,
inclusive).
[0033] Technical and scientific terms used herein have the meaning
commonly understood by one of skill in the art to which the present
application pertains, unless otherwise defined. Reference is made
herein to various methodologies and materials known to those of
skill in the art.
[0034] Luminescent Nanocrystal Phosphors
[0035] Described herein are 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. The terms "nanocrystal," "nanodot," "dot," "quantum dot" and
"QD" 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).
[0036] The material properties of nanocrystals can be substantially
homogenous, 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.
[0037] Nanocrystals, including luminescent nanocrystals, for use in
embodiments described herein can be produced using any method known
to those skilled in the art. Suitable methods and exemplary
nanocrystals are disclosed in U.S. Pat. No. 7,374,807; U.S. patent
application Ser. No. 18/706,832, filed Mar. 10, 2004; U.S. Pat. No.
6,949,206; and U.S. Provisional Patent Application No. 60/578,236,
filed Jan. 8, 2004, the disclosures of each of which are
incorporated, by reference herein in their entireties.
[0038] Luminescent nanocrystals for use in embodiments described
herein 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. 10/790,832, 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.3,N.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.
[0039] In certain embodiments, the nanocrystals may comprise a
dopant from the group consisting of a p-type dopant or an n-type
dopant. The nanocrystals useful herein, 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 and 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.
[0040] The nancrystals, including luminescent nanocrystals, useful
in embodiments described herein can also further comprise ligands
conjugated, cooperated, associated or attached to their surface.
Suitable ligands include any group known to those skilled in the
art, including those disclosed, in U.S. patent application Ser. No.
12/79,813, filed Feb. 4, 2000; U.S. patent application Ser. No.
12/076,530, filed Mar. 19, 2008;. U.S. patent application Ser. No.
12/609,736, filed. Oct. 30, 2009; US. patent application Ser. No.
11/299,299, filed Dec. 9, 2005; U.S. Pat. No. 7,645,397; US. Pat.
No. 7,374,807; U.S. Pat. No. 6,949,206; U.S. Pat. No. 7,572,393;
and U.S. Pat. No. 7,267,875, the disclosures of each of which are
incorporated herein by reference. Use of such ligands can enhance
die 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.
[0041] In certain embodiments, compositions comprising nanocrystals
distributed or embedded in a matrix material are provided. Suitable
matrix materials can be any material knows, to the ordinarily
skilled artisan, including polymeric materials, organic and
inorganic oxides. Compositions described herein can be layers,
encapsulants. coatings, sheets or films. It should be understood
that in embodiments described herein where reference is made to a
layer, polymeric layer, matrix, sheet or film, these terms are used
interchangeably, and the embodiment so described is not limited to
any one type of composition, but encompasses any matrix material or
layer described herein or known in the art.
[0042] Down-converting nanocrystals (for example, as disclosed in
U.S. Pat. No. 7,374,807) utilise 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).
[0043] While any method known to the ordinarily skilled artisan can
be used to create nanocrystals (luminescent nanocrystals),
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.
[0044] 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.
[0045] 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
[0046] 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 1
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.
[0047] 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
nueleation of nanocrystals of the shell materials. Surfactants in
the reaction mixture are present to direct the controlled growth of
shell material and to ensure solubility. A uniform and epetaxially
grown shell is obtained when there is a low lattice mismatch
between the two materials.
[0048] 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, GsAs, 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, Cul,
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, AlCO, 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, InP/ZnSe, PbSe/PbS, CdSe/CdS, CdTe/CdS,
CdTe/ZnS, as well as others.
[0049] As used throughout, a plurality of phosphors or a plurality
of luminescent nanocrystals means more than one phosphor or
luminescent nanocrystal (i.e., 2, 3, 4, 5, 10, 106, 1,000,
1,000,000, etc., nanocrystals). The compositions will suitably
comprise phosphors or luminescent nanocrystals having the same
composition, though in former embodiments, the plurality of
phosphors or luminescent nanocrystals can be various different
compositions. For example, the luminescent nanocrystals can be emit
at the same wavelength, or in further embodiments, the compositions
can comprise luminescent nanocrystals that emit at different
wavelengths.
[0050] Luminescent nanocrystals for use in the embodiments
described, herein 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. As used herein,
blue light comprises light between about 435 nm and about 500 nm,
green light comprises light between about 320 nm and 565 nm and red
light comprises light between about 625 nm and about 740 nm in
wavelength.
[0051] In 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.
[0052] While luminescent nanocrystals of any suitable material can
be used in the various embodiments described herein, in certain
embodiments, the nanocrystals can be ZnS, InAs or CdSe nanocrystals
for 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, InP/ZnSe, CdSe/CdS or InP/ZnS.
[0053] In embodiments, the luminescent nanocrystals will include at
least one population of luminescent nanocrystals capable of
emitting red light and at least one population of luminescent
nanocrystals capable of emitting green light upon excitation by a
blue light source. The luminescent nanocrystal wavelengths and
concentrations can be adjusted to meet the optical performance
required. In still other embodiments, the luminescent nanocrystals
phosphor material can comprise a population of luminescent
nanocrystals which absorb wavelengths of light having undesirable
emission wavelengths, and reemit secondary light having a desirable
emission wavelength, in this manner, the luminescent nanocrystal
films described herein comprise at least one population, of
color-filtering luminescent nanocrystals to further tune the
lighting device emission and to reduce or eliminate the need for
color filtering.
[0054] Suitable luminescent nanocrystals, methods of preparing
luminescent nanocrystals, including the addition of various
solubility-enhancing ligands, can be found in Published U.S. Patent
Application No. 2012/0113672, the disclosure of which is
incorporated by reference herein in its entirety.
Display Systems
[0055] In embodiments, various display systems are provided herein
that are suitably used in any number of applications. As used
herein, a "display system" refers an arrangement of elements that
allow for the visible representation of data on a display. Suitable
displays include various flat, curved or otherwise-shaped screens,
films, sheets or other structures for displaying information
visually to a user. Display systems described herein can be
included in, for example, devices encompassing, a liquid, crystal
display (LCD), televisions, computers, mobile phones, smart,
phones, personal digital assistants (PDAs), gaming devices,
electronic reading devices, digital cameras, and the like.
[0056] An exemplary display system 100 is shown in FIG. 1A. In
embodiments, display system 100 comprises one or more blue light
emitting diode(s) (LED) 102. Various orientations and components of
LEDs are well known to those of ordinary skill in the art. Blue
LEDs described herein suitably emit in the range of 440-470 nm. For
example, the blue LEDs can be GaN LEDs such as a GaN LED which
emits blue light at a wavelength of 450 nm.
[0057] As shown in FIG. 1A, display system 100 also comprises light
guide plate 104. Suitably, light guide plate 104 is optically
coupled to the one or more blue LEDs in the display systems
described throughout.
[0058] As used herein the following terms are used interchangeably,
"light guide plate," "light guide," or "light guide panel," and
refer to an optical component that is suitable for directing
electromagnetic radiation (light) from one position to another.
Exemplary light guide plates include fiber optic cables, polymeric
or glass solid bodies such as plates, films, containers, or other
structures. The size of the light guide plate will depend on the
ultimate application and characteristics of the LED. In general,
the thickness of the light guide plate will be compatible with
thickness of the LED. The other dimensions of the light guide plate
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 guide plates 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.
[0059] Suitable light guide plate materials include polycarbonate
(PC), poly methylmethacrylate (PMMA), methyl methacrylate, styrene,
acrylic polymer resin, glass, or any suitable light guide plate
materials town in the art. Suitable manufacturing methods for the
light guide plate include injection molding, extrusion, or other
suitable embodiments known in the art. In exemplary embodiments,
the light guide plate provides uniform primary light emission from,
the top surface of the light guide plate, such that primary light
entering the luminescent nanocrystal film is of uniform color and
brightness. The light guide plate ears include, any thickness or
shape known in the art. For example, the light guide plate
thickness can be uniform over the entire light guide plate surface.
Alternatively, the light guide plate can have a wedge-like
shape.
[0060] As used herein, "optically coupled" means that components
(e.g., a light guide plate and an 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 components such as a light guide plate and an LED are in
direct physical contact, or as shown in FIG. 1A, the light guide
plate 104 and the LED 102 are each in contact with an optically
transparent element 118. The optically transparent element may
comprise tape or adhesive, including various glues, polymeric
compositions such as silicones, etc. placed between the light guide
plate 104 and the LED 102 to optically couple the elements.
Additional optically transparent adhesives that can be used in
embodiments described herein include various polymers, 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.
[0061] In further embodiments, optical coupling can be
accomplished, for example, by utilising a polymeric light guide
plate, that when heated, melts or deforms such that an LED can be
contacted to the light guide plate, and then the light guide plate
cooled, thereby facilitating the formation of a physical adhesion,
or contact between the two elements. In further embodiments,
optical coupling can be achieved with blue LEDs that have an
encapsulant protruding from the LED, for example a protruding
polymer surface filled with a compliant encapsulation polymer
having a refractive index similar to the refractive index of the
light guide plate. In such embodiments, when the light guide plate
is pressed against the blue LED, an optical coupling is formed
directly between the light guide plate and the LED via the
protruding encapsulant, i.e., the encapsulation polymer.
[0062] It should be noted that while optical coupling does not
require physical interaction between the components, suitably
physical interaction does occur, and suitably involves contact and
is facilitated by an adhering composite (e.g., tape or polymer)
connecting the two components. So long as light is able to pass
between, the components they are considered optically coupled.
[0063] Display system 100, shown in FIG. 1A, also suitably further
comprises a display, for example, liquid crystal module 114. As
used herein, the "display" or "display panel" of the display
systems is the portion of the display output seen by the user or
observer of the display systems.
[0064] Display system 100 also suitably further comprises
composition 106 comprising a plurality of phosphors 122, the
composition oriented between the light guide plate and the display.
As described herein. In embodiments, display system 100 exhibits
increased optical power output as compared to a display system
where the light guide plate is not optically coupled to the blue
LED.
[0065] In embodiments, the display systems described herein,
suitably comprise one or more additional elements traditionally
found in LED-based. display systems. Such elements, as shown in
FIG. 1A, include, but are not limited to, one or more of
diffuser(s) 112 (top or bottom), horizontal brightness enhancement
film(s) (BEF) 110, vertical BEF(s) 108, and reflector(s) 116.
Suitably orientations of these elements, their manufacture and
incorporation in display systems are well known in the art.
[0066] Diffusers, or diffuser films, are distinct from and
supplemental to the scattering features described herein. Diffusers
112 can include any diffuser film known in the art, including gain
diffuser films, and can be disposed above or below the one or more
BEFs 108, 110 or other optical films of the display systems, in
exemplary embodiments, the composition comprising phosphors
(suitably a film comprising luminescent nanocrystals) eliminates
the need for a conventional bottom diffuser film in the display
systems, thereby minimizing the thickness of the lighting device.
The compositions comprising phosphors can also include one or more
scattering or diffuser features associated therewith, which can
serve the purpose of traditional diffusers in addition to
increasing secondary emission, of the phosphors in the
compositions.
[0067] The BEFs and brightness enhancing features can include
reflective and/or refractive films, reflective polarizer films,
prism films, groove films, grooved prism films, prisms, pitches,
grooves, or any suitable BEFs or brightness enhancement features
known in the art. For example, the BEFs can include conventional
BEFs such as Vikuiti.TM.. BEFs available from 3M.TM..
[0068] In exemplary embodiments, the display systems comprise at
least one BEF, more suitably at least two BEFs. Suitably, the
display systems can comprise at least three BEFs. In exemplary
embodiments, at least one BEF comprises a reflective polarizer BEF,
e.g., for recycling light which would otherwise be absorbed by the
bottom polarizer film. The brightness-enhancing features and BEFs
can include reflectors and/or refractors, polarizers, reflective
polarizers, light extraction features, light recycling features, or
any brightness-enhancing features known in the art. The BEFs and
brightness-enhancing features can include conventional BEFs. For
example, the BEFs can include a first layer having pitches or
prisms having a first pitch angle, and at least a second layer
having pitches or prisms having a second pitch angle.
[0069] Reflectors 116 are suitably positioned so as to increase the
amount of light that is emitted from the light guide plate.
Reflectors can comprise any suitable material, such as a reflective
mirror, a film of reflector particles, a reflective metal film, or
any suitable conventional reflectors. In embodiments, reflectors
are suitably a white film. In certain embodiments, the reflectors
can comprise additional functionality or features, such as
scattering, diffuser, or brightness-enhancing features.
[0070] In still further embodiments, as shown in FIG. 1A, the
display systems comprise one or more blue LED 102, light guide
plate 104, optically coupled to blue LED 102, & display (e.g.,
liquid crystal module 114) and a film (e.g., 106) comprising a
plurality of phosphors (122), the composition oriented between, the
light guide plate and the liquid crystal module. Suitably, the
display systems described herein exhibit increased optical power
output and luminous output as compared to a display system where
the light guide plate is not optically coupled to the blue LED.
[0071] As used herein, when describing elements of the various
display systems provided, "oriented between" is meant to indicate
that various elements are positioned relative to one another such
that one element, e.g., a composition comprising phosphors, is
above one element, but below another, in a configuration in which
the elements are in a stack or layered orientation. It should be
understood that other orientations can be mixed in the embodiments
described herein, and can be readily determined by a person of
ordinary skill in the art.
[0072] Exemplary tapes and adhesives for optically coupling light
guide 104 to blue LED 102 are described herein, in additional,
embodiments, the blue LED is coupled to the light guide via an
encapsulant protruding from the LED. In addition, exemplary
phosphors, including various luminescent nanocrystals are described
throughout.
[0073] As described herein, in suitable embodiments, film 106 is a
polymeric film, comprising luminescent nanocrystals. Exemplary
polymers for use in preparing film 106, and methods of preparing
polymeric films comprising luminescent nanocrystals are described
herein.
[0074] Additional elements that can be included in display systems
described herein are described throughout.
[0075] In an additional embodiment of display system 100, shown in
FIG. 1A, described, herein are display systems comprising one or
more blue LED 102, a light guide plate, optically coupled to the
blue LED 104, a polymeric film (e.g., 106) comprising a plurality
of phosphors (122), the polymeric film oriented above the light
guide plate 104, a vertical BEF 108 oriented above the polymeric
film, a horizontal BEF 110 oriented above the vertical BEF 108, a
top diffuser 112 oriented above the horizontal BEF 110, and a
liquid crystal module 114 oriented above the top diffuser 112.
[0076] Suitably, the display systems described herein exhibit
increased optical power output as compared to a display system
where the light guide plate is not optically coupled to the blue
LED. In embodiments, display systems described herein exhibit an
optical power output of at least 26 mW/LED, more suitably at least
28 mW/LED, or at least 29 mW/LED at a driving current of 20 mA.
[0077] Exemplary methods and compositions for preparing the optical
coupling are described herein, as are exemplary phosphors including
luminescent nanocrystals.
[0078] The display systems described herein can comprise one or
more medium, materials between adjacent elements of the systems.
The system can include one or more medium material disposed between
any of the adjacent elements its the systems, including the LED and
the light guide plate; the light guide plate and the composition
comprising phosphors; between any different layers or regions
within the composition comprising phosphors; the composition
comprising phosphors and one or more barrier layers; the
composition, comprising phosphors and the light guide plate; the
composition comprising phosphors and one or more BEF, diffuser;
reflector, or other features; and between multiple barrier layers,
or between any other elements of the display systems. The one or
more media can include any suitable materials, including, but not
limited to, a vacuum, air, gas, optical materials, adhesives,
optical adhesives, glass, polymers, solids, liquids, gels, cured
materials, optical coupling materials, index-matching or
index-mismatching materials, index-gradient materials, cladding or
anti-cladding materials, spacers, epoxy, silica gel, silicones, any
matrix materials described herein, brightness-enhancing materials,
scattering or diffuser materials, reflective or anti-reflective
materials, wavelength-selective materials, wavelength-selective
anti-reflective materials, color filters, or other suitable media
known in the art. Suitable media materials include optically
transparent, non-yellowing, pressure-sensitive optical adhesives.
Suitable materials include silicones, silicone gels, silica gel,
epoxies (e.g., Loctite.TM. Epoxy E-30CL), actylates (e.g., 3M.TM.
Adhesive 2175), and matrix materials mentioned herein. The one or
more media materials can be applied as a curable gel or liquid and
cured daring or alter deposition, or preformed and pre-cured prior
to deposition. Suitable curing methods include UV curing, thermal
curing, chemical curing, or other suitable curing methods known in
the art. Suitably, index-matching media materials can be chosen to
minimize optical losses between elements of the lighting
device.
[0079] In additional embodiments, display systems are provided in
which a container comprising a plurality of phosphors is optically
coupled to a blue LED. For example, as shown in display system 160
in FIG. 1B, blue LED 162 is optically coupled at 182, to container
178 that contains a plurality of phosphors 184, for example a
plurality of luminescent nanocrystals as disclosed herein. In
exemplary embodiments, container 178 is a capillary, as described
throughout.
[0080] As shown in FIG. 1B, light guide plate 164 is optically
coupled to container 178 at 182, via glue, mechanical alignment
alone, various adhesives as described throughout, or the like, and
combinations thereof. This can also be accomplished, for example,
by utilizing a polymeric light guide plate, that when heated, melts
or deforms such that hermetically sealed container can be contacted
to the light guide plate, and then the light guide plate cooled,
thereby facilitating the formation of a physical adhesion or
contact between elements (e.g., between LED, light guide plate and
container comprising phosphors). In additional embodiments, the
blue LED is coupled to the light guide via an encapsulant
protruding from the LED.
[0081] In exemplary embodiments, display systems 160 as shown, in
FIG. 1B, can further comprise bottom diffuser 166 oriented above
light guide plate 164, vertical BEF 168 oriented above bottom
diffuser 166, horizontal BEF 170 oriented above vertical BEF 168,
top diffuser 172 oriented above horizontal BEF 170, and liquid
crystal module 174 (i.e., display) oriented above top diffuser 172.
The display systems can also further comprise reflector 176, as
described herein.
Compositions of Phosphors
[0082] As used herein, the term "phosphors" refers to a synthetic
fluorescent or phosphorescent substance. Exemplary phosphors
include traditional materials such as cerium(II)-doped YAG
phosphors (YAG:Ce.sup.3+, or Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+), as
well as luminescent nanocrystals, as described herein. Additional
phosphors that can be utilized in the devices described herein
include, but are not limited to, silicate phosphors, garnet
phosphors, aluminate phosphors, nitride phosphors, NYAG phosphors,
SiAlON phosphors and CaAlSiN.sub.3-based (CASN) phosphors, as well
as other phosphors known in the art.
[0083] As described throughout, compositions comprising phosphors
for use in embodiments provided can take numerous shapes, including
for example, films or sheets (e.g. composition 106 of FIG. 1A). In
further embodiments, the compositions can be various containers or
receptacles for receiving the phosphors, suitably luminescent
nanocrystals.
[0084] Suitably, phosphors, and specifically luminescent
nanocrystals, are dispersed or embedded in suitable polymeric
materials to create films or sheets, also called quantum dot
enhancement films (QDEFs). Such films are described, for example,
in Published U.S. Patent Application Nos. 2010/0110728 and
2012/0113672, the disclosures of each of which are incorporated by
reference herein in their entireties.
[0085] The luminescent nanocrystals are suitably coated with one or
more ligand coatings, embedded in one or more films or sheets,
and/or sealed by one or more barrier layers. Such ligands, films,
and barriers can provide photostability to the luminescent
nanocrystals and protect the luminescent nanocrystals from
environmental conditions including elevated temperatures, high
intensity light, external gases, moisture, and other harmful
environmental conditions. Additional effects can be achieved with
these materials, including a desired index of refraction in the
host film material, a desired viscosity or luminescent nanocrystal
dispersion/miscibility in the host film material, and other desired
effects. In suitable embodiments, the ligand and film materials
will be chosen to have a sufficiently low thermal expansion
coefficient, such that thermal, curing does not substantially
affect the luminescent nanocrystal phosphor material.
[0086] The luminescent nanocrystals useful herein suitably comprise
ligands conjugated to, cooperated with, associated with, or
attached to their surface. In preferred embodiments, the
luminescent nanocrystals include a coating layer comprising ligands
to protect the luminescent nanocrystals from external moisture and
oxidation, control aggregation, and allow for dispersion of the
luminescent nanocrystals in the matrix material. Suitable ligands
and matrix materials, as well as methods for providing such
materials, are described herein. Additional suitable ligands and
film materials, as well as methods for providing such materials,
include any group known to those skilled in the art, including
those disclosed in Published U.S. Patent Application No.
2012/0113672; U.S. patent application Ser. No. 12/79,813, filed
Feb. 4, 2000; U.S. patent application Ser. No. 12/070,530, filed
Mar. 19, 2008: U.S. patent application Ser. No. 12/600,736, filed
Oct. 30, 2009; U.S. patent application Ser. No. 11/299,299, filed
Dec. 9, 2005; U.S. Pat. No, 7,645,397; U.S. Pat. No. 7,374,807;
U.S. Pat. No. 6,949,206; U.S. Pat. No. 7,572,393; and U.S. Pat. No.
7,267,875, the disclosure of each of which is incorporated herein
by reference in its entirety. Additionally, suitable ligand and
matrix materials include any suitable materials in the art.
[0087] Dispersing luminescent nanocrystals in a polymeric material
provides a method to seal the nanocrystals and provide a mechanism
for mixing various compositions and sizes of luminescent
nanocrystals. As used throughout, "dispersed" includes uniform
(i.e., substantially homogeneous) as well as non-uniform (i.e.,
substantially heterogeneous) distribution or placement of
luminescent nanocrystals.
[0088] Suitable materials for use in the compositions comprising
the luminescent nanocrystals include polymers and organic and
inorganic oxides. Suitable polymers include any polymer known to
the ordinarily skilled artisan that can be used tor such a purpose.
In suitable embodiments, the polymer will be substantially
translucent or substantially transparent. Suitable matrix materials
include, but are not limited to, epoxies; acrylates; norborene;
polyethylene; poly(vinyl butyral):poly(vinyl acetate); polyurea;
polyurethanes; silicones and silicone derivatives including, but
not limited to, amino silicone (AMS), polyphenylmethylsiloxane,
polyphenylalkylsiloxane. polydiphenylsiloxane, polydialkylsiloxane,
silsesquioxanes, 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
such as polystyrene, amino polystyrene (APS), and
poly(acrylonitrile ethylene styrene) (AES); polymers that are
crosslinked with difunctional monomers, such as divinylbenzene;
cross-linkers suitable for cross-linking ligand materials; epoxides
which combine with ligand amines (e.g., APS or PEI ligand amines)
to form, epoxy, and the like.
[0089] The luminescent nanocrystals as described herein can be
embedded in a polymeric (or other suitable material, e.g., waxes,
oils) matrix using any suitable method, for example, mixing the
luminescent nanocrystals in a polymer and casting a film; mixing
the luminescent nanocrystals with monomers and polymerizing them
together; mixing the luminescent nanocrystals in a sol-gel, 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, it should,
be noted that luminescent nanocrystals are suitably uniformly
distributed throughout the composition, though in further
embodiments they can be distributed according to an
application-specific umformity distribution function.
[0090] The thickness of the compositions comprising luminescent
nanocrystals as described herein can be controlled by any method
known in the art, such as spin coating and screen printing. The
luminescent nanocrystal compositions as described herein 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 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 films can be on the order of 10's
to 100's of microns in thickness. The luminescent nanocrystals can
he embedded in the various compositions 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, polymer 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.
Containers Comprising Phosphors
[0091] In further embodiments, the compositions comprising
phosphors are containers comprising a plurality of luminescent
nanocrystals. As used herein, a "container" 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 he used to form the containers for use in the
embodiments described herein. 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.
[0092] In embodiments, a polymeric or glass tube can be used as a
container. A solution of luminescent nanocrystals can then be drawn
into the container by simply applying a reduced pressure to an end
of the container. The container can then be sealed by heating and
"pinching" the container at various sealing positions or seals
throughout the length of the container, or by using other sealing
mechanisms as described throughout. In this way, the container can
be separated into various individual sections. These sections can
either be retained together as a single, sealed container, or the
sections can be separated into individual pieces. Hermetic sealing
of the container can be performed such that each individual seal
separates solutions of the same nanocrystals. In other embodiments,
seals can be created such that separate sections of the container
each contain a different nanocrystal solution (i.e., different
nanocrystal composition, size or density).
[0093] In embodiments, the container is suitably a plastic or glass
container. In suitable embodiments, the 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 display devices
described herein 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.
[0094] Suitably, capillaries described herein have 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 plate. Suitably,
a capillary has a height (in the plane of the light guide plate) 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 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, or about 1 mm to about 10 mm.
[0095] The concentration of luminescent nanocrystals In the
containers described herein depends on the application, size of the
luminescent nanocrystals, composition of the luminescent
nanocrystals, the composition of polymeric matrix in which the
luminescent nanocrystals are dispersed, 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.
Display Systems Exhibit Increased Optical Power Output and
Increased Luminous Output
[0096] As described herein and particularly in the Examples,
display systems described herein exhibit increased optical power
output and increased luminous output as compared to a display
system where the light guide plate is not optically coupled to the
blue LED. As used herein "optical power output"is defined to be the
total power emitted by an LED per unit time, per LED, when driven
at a constant, current. Optical power output is suitably expressed
as Watts/LED (suitably mW/LED). A person of ordinary skill in the
art will readily understand that optical power output cars also he
calculated at various driving currents, so long as comparative
measurements are appropriately made at the same driving
current.
[0097] As used herein "luminous output" is defined to be the total
amount of visible light emitted by a display system. Luminous
output, as described herein, is measured in lumens.
[0098] As used herein "increased optical power output" when
referring to the display systems described herein, is used to
indicate that the display systems demonstrate greater than at least
3% more optical power as compared to a display system where the
light guide plate is not optically coupled to the blue LED. More
suitably, the disclosed display systems provide at least 4%, at
least 5%, at least 6%, at least 7%, at least 8%, at least 9%, at
least 10%, at least 11%,, at least 17%, at least 13%, at least 14%,
at least 15%, at least 16%, at least 17%, at least 18%, at least
10%, or at least 20% more optical power as compared to a display
system where the light guide plate is not optically coupled to the
blue LED. In other embodiments, the disclosed display systems
demonstrate an increased optical power output of about 3% to about
20%, about 5% to about 20%, about 5% to about 15%, about 3% to
about 12%, about 5% to about 11%, about 6%, to about 14%, about 7%
to about 13%, about 8% to about 12%, about 9% to about 11%, about
7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%,
about 14% or about 15%, as compared to a display system where the
light guide plate is not optically coupled to the blue LED,
including any values and ranges within the recited values.
[0099] As used herein "increased luminous output" when referring to
the display systems described herein, is used to indicate that, the
display systems demonstrate greater than at least 3% more luminous
output as compared to a display system where the light guide plate
is not optically coupled to the blue LED. More suitably, the
disclosed display systems provide at least 4%, at least 5%, at
least 6%, at least 7%, at least 8%, at least 9%, at least 10%, at
least 11%, at least 12%, at least 13%, at least 14%, at least 15%,
at least 16%, at least 17%, at least 18%, at least 19%, or at least
20% more luminous output as compared to a display system where the
light guide plate is not optically coupled to the blue LED. In
other embodiments, the disclosed display systems demonstrate an
increased luminous output of about 3% to about 20%, about 5% to
about 20%, about 5% to about 15%, about 5% to about 12%, about 5%
to about 11%, about 6% to about 14%, about 7% to about 13%, about
8% to about 12%, about 9% to about 11%, about 7%, about 8%, about
9%, about 10%, about 11%, about 32%, about 13%, about 14% or about
15%, as compared to a display system where the light guide plate is
not optically coupled to the blue LED, including any values and
ranges within the recited values.
[0100] In further embodiments, the disclosed display systems in
which a container comprising a plurality of phosphors is optically
coupled to a blue LED and optically coupled to a light guide plate
provide at least 4%, at least 5%, at least 6%, at least 7%, at
least 8%, at least 9%, at least 10%, at. least 11%, at least 12%,
at least 13%, at least 14%, at least 15%, at least 16%, at least
17%, at least 18%, at least 19%, or at least 20% snow optical power
as compared to a display system where a container comprising a
plurality of phosphors is not optically coupled to a blue LED and
is not optically coupled to a light guide plate. In other
embodiments, the disclosed display systems demonstrate an increased
optical power output of about 3% to about 20%, about 5% to about
20%, about 5% to about 15%, about 5% to about 12%, about 5% to
about 11%, about 6% to about 14%, about 7% to about 13%, about 8%
to about 12%, about 9% to about 11%, about 7%, about 8%, about 9%,
about 10%, about 11%, about 12%, about 13%, about 14% or about 15%,
as compared to a display system where a container comprising a
plurality of phosphors is not optically coupled to a blue LED and
is not optically coupled to a light guide plate., including any
values and ranges within the recited values.
[0101] In further embodiments, the disclosed display systems in
which a container comprising a plurality of phosphors is optically
coupled to a blue LED and optically coupled to a light guide plate
provide at least 4%, at least 5%, at least 6%, at least 7%, at
least 8%, at least 9%, at least 10%, at least 11%, at least 12%, at
least 13%, at least 14%, at least 15%, at least 16%, at least 17%,
at least 18%, at least 19%, or at least 20% more luminous output as
compared to a display system where a container comprising a
plurality of phosphors is riot optically coupled to a blue LED and
is not optically coupled to a light guide plate. In other
embodiments, the disclosed display systems demonstrate an increased
luminous output of about 3% to about 20%, about 5% to about 20%,
about 5% to about 15%, about 5% to about 32%, about 5% to about
11%, about 6% to about 14%, about 7% to about 13%, about 8% to
about 12%, about 9% to about 11%, about 7%, about 8%, about 9%,
about 10%, about 11%, about 12%, about 13%, about 14% or about 15%,
as compared to a display system, where a container comprising a
plurality of phosphors is not optically coupled to a blue LED and
is not optically coupled to a light guide plate, including any
values and ranges within- the recited values.
Methods of Increasing Optical Power Output and Luminous Output
[0102] As described herein, display systems are provided that
improve blue light extraction, efficiency from, blue LEDs. In
embodiments, the blue LEDs are optically coupled to a light guide
plate. Such optical coupling removes the polymer/air interfaces,
thereby suitably preventing blue light from, back-reflection and
subsequent absorption by the blue die (120 of FIG. 1A).
Improvements in optical power output and luminous output are
described throughout.
[0103] Reduction or elimination of blue light reflection brings the
additional benefit of lowering the blue flux on LED package
sidewalls, which extends the lifetime of the LED package. In
addition, reduction of blue light absorption by the LED die can
reduce the die temperature, which can further increase its
efficiency and extend the LED lifetime.
[0104] In still further embodiments, methods of increasing the
optical power output end luminous output of a blue LED in a display
system are provided. Such methods suitably comprise optically
coupling the blue LED to a light guide plate of the display system.
Exemplary methods and compositions for use in optical coupling,
including tape and various adhesives, are provided herein. In
additional embodiments, the blue LED is coupled to the light guide
via an encapsulant protruding from the LED.
[0105] As described herein, the methods suitably increase dee
optical power output of a blue LED in a display system by greater
than at least 3% as compared to a display system where the light
guide plate is not optically coupled to the blue LED. More
suitably, the methods increase the optical power by at least 4%, at
least 5%, at least 6%, at least 7%, at least 8%, at least 9%, at
least 10%, at least 11%, at least 12%, at least 13%, at least 14%,
at least 15%, at least 16%, at least 17%, at least 18%, at least
19%, or at least 20% as compared to a display system where the
light guide plate is not optically coupled to the blue LED. In
other embodiments, the methods described herein provide an
increased optical power output of about 3% to about 20%, about 5%
to about 20%, about 5% to about 15%, about 5% to about 12%, about
5% to about 11%, about 6% to about 14%, about 7% to about 13%,
about 8% to about 12%, about 9% to about 11%, about 7%, about 8%,
about 9%, about 10%, about 11%, about 12%, about 13%, about 14% or
about 13%, as compared to a display system where the light guide
plate is not optically coupled to the blue LED, including any
values and ranges within the recited values.
[0106] As described, herein, the methods suitably increase the
luminous output of a blue LED in a display system by greater than
at least 3% as compared to a display system where the light guide
plate is not optically coupled to the blue LED, More suitably, the
methods increase the luminous output by at least 4%, at least 5%,
at least 6%, at least 7%, at least 8%, at least 9%, at least 10%,
at least 11% at least 12%, at least 13%, at least 14%, at least
15%, at least 16%, at least 17%, at least 18%, at least 19%, or at
least 20% as compared to a display system where the light guide
plate is not optically coupled to the blue LED. In other
embodiments, the methods described herein provide an increased
luminous output of about 3% to about 20%, about 5% to about 20%,
about 5% to about 15%, about 5% to about 12%, about 5% to about
11%, about 6% to about 14%, about 7% to about 13%, about 8% to
about 12%, about 9% to about 11%, about 7%, about 8%, about 9%,
about 10%, about 11%, about 12%, about 13%, about 14% or about 15%,
as compared to a display system where the light guide plate is not
optically coupled to the blue LED, including any values and ranges
within the recited values.
[0107] It will be readily apparent to one of ordinary skill in the
relevant arts that other suitable modifications and adaptations to
the methods and applications described herein can be made without
departing from the scope of any of the embodiments. The following
examples are included herewith for purposes of illustration, only
and are not intended to be limiting.
EXAMPLES
Example 1: Increased Power Output From Blue LEDs by Optical
Coupling to a Light Guide Plate
[0108] Generally, liquid crystal displays utilize white LEDs as the
light source in the backlight. Most backlights are edge-lit--the
white LEDs are placed, on the edge(s) of the backlight. The white
LEDs are mounted on a flex strip and placed in close proximity to a
light guide plate. White light coming out of the LEDs enters the
light guide plate from the edge and, through total internal
reflections, is guided across the light guide plate. Extraction
features are molded on the surface of the light guide plates to
extract light from the light guide plate to enable a uniform
distribution of light across the display. Phosphors are often
introduced that offer better system efficiency and/or higher color
gamut.
[0109] As described herein, luminescent nanocrystals (quantum dots)
are dispersed/embedded in a polymeric film or sheet (quantum dot
enhancement film (QDEF)) and placed on top of a light guide plate.
White LEDs are replaced by blue LEDs (FIG. 1A). (See Published U.S.
Patent Application No. 2012/0113672, the disclosure of which is
incorporated by reference herein in its entirety.) When color gamut
is matched at 72% National Television System Committee (NTSC). for
example, luminescent nanocrystals plus blue-LEDs deliver 15-20%
higher power efficiency compared to white LEDs as a result of
better spectral distribution of the backlight of tire QDEF that
matches the color filters, which enables the use of higher
transmission color filters.
[0110] To convert from white LEDs to blue LEDs, a clear
encapsulation polymer is utilized inside the LED package instead of
using YAG-impregnated encapsulation polymer. Doing so, however, has
an unintended consequence of lowering the out-coupling efficiency
of the LED. As shown in FIGS. 2A-2C, for white LEDs (FIG. 2A), much
of the blue light is converted to yellow by the YAG phosphor in the
encapsulation polymer. When the yellow photons are reflected back
towards the LED die, the yellow photons are not absorbed since they
are below die band gap of the die material.
[0111] In the case of blue LED (FIG. 2B), in contrast, the blue
photons that are reflected off the encapsulation polymer and air
interface can re-enter the die 120 and can be absorbed. As a
result, the blue out-coupling efficiency is lower than that of the
white LED.
[0112] To estimate the out-coupling efficiency loss, the total
optical output of a white LED and a blue LED using nominally the
same efficiency blue die were determined. From theoretical
calculations (FIGS 3A-3B), if the YAG quantum efficiency is at the
theoretical limit of 100%, the total Optical power of a white LED
should be close to 85% of a blue LED if the out-coupling
efficiencies are the same in both cases. This is because the yellow
photons are lower in energy (550 nm corresponds to 2.25 eV) than a
blue photon (450 nm corresponds to 2.76 eV). To convert from blue
to white, the majority of the blue photons (higher energy) need, to
be downshifted to yellow photons (lower energy) where the energy
difference is dissipated as heat. In reality, current YAG phosphor
material has quantum efficiency of close to 90%. The expected power
output from a white LED should he close to 80% that of the
blue.
[0113] In the measurements conducted on white LEDs and blue LEDs
coming from the same vendor, using the same ranked dies, and using
the same packages, the surprising result was observed that the
white LED power output is actually almost the same as that of the
blue (Table 1).
TABLE-US-00001 TABLE 1 Table 1: Experimental measurements of total
optical power from white LEDs and blue LEDs from the same vendor,
using the same rank die, same package, and driven at the same
current. Measurements were done in an integrating sphere.
Integrated optical power output (mW) White LED driven at 20 mA 24.5
Blue LED driven at 20 mA 25.3
[0114] Similar results were obtained on LEDs from different
vendors. This indicates that she light extraction efficiency from
die blue LED package is significantly worse than that of the white
LED package. This lower extraction efficiency is likely a result of
the reflection of the blue light from the encapsulation/air
interface and absorption of the blue light from the die (as shown
in FIG. 2B). These results suggest that improving the out-coupling
of the blue LEDs can increase the power output by close to 20%, for
example up to 29-30 mW/LBD or mom (at a driving current of 20
roA).
[0115] To improve light extraction, efficiency from blue LEDs and
coupling efficiency to the light guide plate, blue LEDs are
optically coupled to the light guide plate using a thin optically
clear adhesive (e.g., silicone).
[0116] As illustrated in FIG. 2C, this optically clear adhesive,
when index-matched to the LED encapsulation polymer and light guide
plate, eliminates the reflections from two interfaces: the LED
encapsulation/air interface and air/light-guide-pate interface. As
a result, the blue light emitted by the blue die directly enters
the light guide plate without suffering from reflection losses and
absorption losses (i.e., from the blue die).
[0117] Optically coupling a white LED and a light guide plate was
found to reduce brightness, likely due to the white LED's higher
light extraction efficiency. See FIG. 2A. This is illustrated in
the results for coupled and uncoupled brightness as demonstrated in
Table 2.
TABLE-US-00002 TABLE 2 Uncoupled Coupled White Point (0.2891,
0.2769) (0.2681, 0.2463) Brightness 5690 nits 4790 nits
[0118] In the coupled case, the brightness is actually lower and
the white point is cooler. The reason for this is that the blue
light is able to escape the package out of the first pass when,
coupled to the light-guide plate. In the uncoupled case, winch is
the intended use configuration, some of the blue light is reflected
off the encapsulation/air interface and goes back into the package.
This reflection, enables more of the blue light to be absorbed by
the yellow phosphors in the LED cup, which makes the white point
warmer.
[0119] However, with blue LEDs, a 14% total increase in efficiency
by optical coupling is demonstrated by the following set of
experiments (see Table 3). A surprising and unexpected result of
the embodiments described herein that has heretofore not been
necessary or beneficial when using white LEDs for display systems
which did not utilize films comprising luminescent
nanocrystals.
[0120] In case 1, a flex strip with 25 blue LEDs is placed in an
integrating sphere. When driven with 20 mA per LED, a total,
optical power of 673 mW is measured. In case 2, a light guide plate
(LGP) is abutted against the LED strip (as in a back light) without
use of an adhesive to provide the optical coupling. The integrated
optical power in case 2 is 645 mW, a 4% reduction. compared to case
1 with the bare flex. This reduction is likely a result of the
reflection from the air/LGP interface sending some of the blue
light back towards the LED and the flex strip leading to losses. In
case 3, the LEDs are optically coupled to the light guide plate
using an optically clear adhesive. The total integrated blue light
is 737 mW, which is 9% higher than, case 1 with the bare flex and
14% higher than case 2 with the LGP uncoupled, to the LEDs, in case
3, the optical power output of 29.5 mW/LED is achieved.
TABLE-US-00003 TABLE 3 Table 3: Measured optical power output in
integrating sphere of a flex strip with 25 blue LEDs driven at 20
mA. Power Flex/LED Ratio to LGP (mW) Ratio to flex w/o coupling
Flex w/o LGP 673/26.9 100% LGP w/o adhesive- 645/25.8 96% 100%
based optical coupling LGP w/coupling 737/29.5 109% 114%
[0121] In order to achieve good optical coupling when the blue LEDs
and the light guide plate were joined with the adhesive layer,
their surfaces were prepared, as follows. First, a small amount of
silicone was added to the encapsulation polymer of each blue LED
package. This treatment reduced the possibility of air gaps at the
adhesive/LED interface. The possibility of air gaps in currently
manufactured. LEDs is increased due to the fact that they have
concave surfaces. The possibility of air gaps would he reduced if a
convex LED encapsulation surface were used and such a convex
surface is preferred. Second, the edge of the light guide plate was
polished to a flat surface from its original lenticular surface to
enable good optical coupling with minimal air gaps. A thin strip of
optically-clear adhesive was applied between the modified blue LED
strip and the polished light guide plate to provide an
adhesive-based optical coupling. The particular adhesive used in
this experiment was a 3M optically clear adhesive 8146-x with 50 um
thickness.
[0122] Comparison of optically-coupled and non-coupled (i.e.,
without adhesive coupling) configurations demonstrated that,
eliminating the original lenticular surface form the edge of the
light guide plate did not significantly change the light mixing
distance. (See FIGS. 4A and 4B). Furthermore, the backlight
appeared homogeneous without any noticeable streaks close to the
LEDs in a folly assembled backlight assembly that included QDEF and
horizontal and vertical BEFs placed on top of the light guide
plate, (FIG. 4C).
[0123] By combining the benefits of a high-efficiency QDEF and
better out-coupled blue LEDs, the next generation LCD backlights
can enable >30% energy savings compared to the current
generation. LCDs at the same color gamut, e.g., sRGB. Even for high
color gamut displays, e.g., Adobe-RGB and DCIP3, higher efficiency
LCDs can be achieved compared to today's sRGB LCDs, in addition to
other benefits, such increases can enable the use of smaller
batteries in various mobile devices.
[0124] It is to be understood, that while certain embodiments have
been illustrated and described herein, the claims are not to be
limited to the specific forms or arrangement of parts described and
shown. In the specification, there have been disclosed illustrative
embodiments and although specific terms are employed, they are used
in a generic and descriptive sense only and not for purposes of
limitation. Modifications and variations of the embodiments are
possible in light of the above teachings. It is therefore to be
understood that the embodiments may be practiced otherwise than as
specifically described.
* * * * *