U.S. patent application number 13/575845 was filed with the patent office on 2013-07-18 for lighting devices with prescribed colour emission.
This patent application is currently assigned to Yissum Research Development Company of the Hebrew University of Jerusalem. The applicant listed for this patent is Hagai ARBELL, Uri BANIN. Invention is credited to Hagai ARBELL, Uri BANIN.
Application Number | 20130181234 13/575845 |
Document ID | / |
Family ID | 43977923 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130181234 |
Kind Code |
A2 |
ARBELL; Hagai ; et
al. |
July 18, 2013 |
LIGHTING DEVICES WITH PRESCRIBED COLOUR EMISSION
Abstract
Optical conversion layers based on semiconductor nanoparticles
for use in lighting devices, and lighting devices including same.
In various embodiments, spherical core/shell seeded nanoparticles
(SNPs) or nanorod seeded nanoparticles (RSNPs) are used to form
conversion layers with superior combinations of high optical
density (OD), low re-absorbance and small FRET. In some
embodiments, the SNPs or RSNPs form conversion layers without a
host matrix. In some embodiments, the SNPs or RSNPs are embedded in
a host matrix such as polymers or silicone. The conversion layers
can be made extremely thin, while exhibiting the superior
combinations of optical properties. Lighting devices including SNP
or RSNP-based conversion layers exhibit energetically efficient
superior prescribed colour emission
Inventors: |
ARBELL; Hagai; (Jerusalem,
IL) ; BANIN; Uri; (Mevaseret Zion, IL) |
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Applicant: |
Name |
City |
State |
Country |
Type |
ARBELL; Hagai
BANIN; Uri |
Jerusalem
Mevaseret Zion |
|
IL
IL |
|
|
Assignee: |
Yissum Research Development Company
of the Hebrew University of Jerusalem
Jerusalem
IL
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130026506 A1 |
January 31, 2013 |
|
|
Family ID: |
43977923 |
Appl. No.: |
13/575845 |
Filed: |
January 27, 2011 |
PCT Filed: |
January 27, 2011 |
PCT NO: |
PCT/IB2011/050366 PCKC 00 |
371 Date: |
October 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61299012 |
Jan 28, 2010 |
|
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61299018 |
Jan 28, 2010 |
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Current U.S.
Class: |
257/88 ; 252/500;
252/519.4; 257/E33.061; 428/220; 977/762; 977/773; 977/813 |
Current CPC
Class: |
C09K 11/565 20130101;
H01L 33/505 20130101; Y10S 977/95 20130101; C09K 11/02 20130101;
C09K 11/7706 20130101; C09K 11/56 20130101; B82Y 20/00 20130101;
H01L 33/502 20130101; C09K 11/883 20130101; C09K 11/025 20130101;
Y10S 977/779 20130101; Y10S 977/774 20130101 |
Class at
Publication: |
257/88 ; 252/500;
252/519.4; 428/220; 257/E33.061; 977/813; 977/773; 977/762 |
International
Class: |
H01B 1/06 20060101
H01B001/06; H01B 1/10 20060101 H01B001/10; H01L 33/50 20100101
H01L033/50; H01B 1/00 20060101 H01B001/00 |
Claims
1. An optical conversion layer for use in a lighting device in
which a light source emits light of a first wavelength, the
conversion layer comprising at least one type of semiconductor
nanoparticles having a central emission wavelength (CWL) in the
range 580-700 nm, the conversion layer having an optical density
(OD) between 0.07 and 2 at 450 nm and an absorption ratio (AR) of
absorbance at 455 nm to a maximum value of absorbance in the range
of 560-700 nm greater than 3.5:1, wherein the conversion layer may
be used to convert at least part of the light of the first
wavelength into light of a second wavelength longer than the first
wavelength.
2. The conversion layer of claim 1, wherein the nanoparticles are
seeded nanoparticles (SNPs).
3. The conversion layer of claim 2, wherein the seeded
nanoparticles are nanorod seeded particles (RSNPs).
4. The conversion layer of claim 1, wherein the AR is greater than
7:1.
5. The conversion layer of claim 1, further characterized by at
least one of the following: (i) having an AR between absorbance at
455 nm and a maximum value of absorbance in the wavelength range of
520-580 nm greater than 6:1; (ii) having a photoluminescence (PL)
shift smaller than about 5 nm, wherein the PL shift represents the
difference between a CWL measured in Toluene at OD<0.1 and a CWL
measured in the conversion layer; and (iii) comprising at least one
excess organic ligand not bound to any SNP surface.
6-7. (canceled)
8. The conversion layer of claim 1, wherein the layer is thinner
than about 2 .mu.m.
9. (canceled)
10. The conversion layer of claim 1, wherein the semiconductors are
selected from the group consisting of II-VI, III-V IV-VI and
III-VI.sub.2 semiconductors.
11. The conversion layer of claim 2, wherein the SNPs or RSNPs have
at least one of the following configurations: (a) comprise a
core/shell structure with materials selected from the group
consisting of CdSe/CdS, CdSeS/CdS, ZnSe/CdS, ZnCdSe/CdS,
CdSe/CdZnS, CdTe/CdS, InP/ZnSe, InP/CdS, InP/ZnS and
CuInS.sub.2/ZnS; (b) a core/double shell structure with materials
selected from the group consisting of CdSe/CdS/ZnS, CdSe/CdZnS/ZnS,
ZnSe/CdS/ZnS, InP/ZnSe/ZnS, InP/CdS/ZnS and InP/CdZnS/ZnS
12. (canceled)
13. The conversion layer of claim 1, further comprising a host
material which incorporates the nanoparticles.
14. The conversion layer of claim 13, wherein the host material is
a polymer or a silicone.
15. The conversion layer of claim 14, wherein the layer is thinner
than about 5000 .mu.m.
16-17. (canceled)
18. The conversion layer of claim 1, wherein the at least one type
of nanoparticles includes a plurality of types, each type
performing conversion into light of a different wavelength longer
than the first wavelength.
19. An optical conversion layer for use in a lighting device in
which a light source emits light of a first wavelength, the
conversion layer comprising at least one type of semiconductor
nanoparticles having a central emission wavelength (CWL) in the
range 520-580 nm, the conversion layer characterized by having an
optical density (OD) between 0.05 and 2 at 405 nm and an absorption
ratio (AR) of absorbance at 405 nm to a maximum value of absorbance
in the range 520-600 nm greater than 3.5:1, wherein the conversion
layer may be used to convert at least part of the light of the
first wavelength into light of a second wavelength longer than the
first wavelength.
20. The conversion layer of claims 19, wherein the nanoparticles
are seeded nanoparticles (SNPs).
21. The conversion layer of claim 20, wherein the seeded
nanoparticles are nanorod seeded particles (RSNPs).
22. The conversion layer of claim 19, wherein the AR is higher than
7:1.
23. The conversion layer of claim 19, further characterized by at
least one of the following: (1) having a photoluminescence (PL)
shift smaller than about 5 nm, wherein the PL shift represents the
difference between a CWL measured in Toluene at OD<0.1 and a CWL
measured in the conversion layer; (2) comprising at least one
excess organic ligand not bound to any SNP surface.
24. (canceled)
25. The conversion layer of claim 19, wherein the layer is thinner
than about 5 .mu.m.
26. (canceled)
27. The conversion layer of claim 1, characterized by at least one
of the following: (a) the semiconductors are selected from the
group consisting of II-VI, III-V IV-VI and I-III-VI.sub.2
semiconductors; (b) the nanoparticles are seeded nanoparticles
(SNPs), the SNPs or RSNPs having a core/shell structure with
materials selected from the group consisting of CdSe/CdS, ZnSe/CdS,
CdSe/CdZnS, CdTe/CdS, InP/ZnSe, InP/CdS, InP/ZnS and
CuInS.sub.2/ZnS; (c) the nanoparticles are seeded nanoparticles
(SNPs), the SNPs or RSNPs having a core/double shell structure with
materials selected from the group consisting of CdSe/CdS/ZnS,
CdSe/CdZnS/ZnS, ZnSe/CdS/ZnS, InP/ZnSe/ZnS, InP/CdS/ZnS and
InP/CdZnS/ZnS
28-29. (canceled)
30. The conversion layer of claim 20, further comprising a host
material which incorporates the nanoparticles.
31. The conversion layer of claim 30, wherein the host material is
a polymer or a silicone.
32. The conversion layer of claim 31, wherein the layer is thinner
than about 5000 .mu.m.
33-34. (canceled)
35. An optical conversion layer for use in a lighting device in
which a light source emits light of a first wavelength, the
conversion layer comprising at least two different types of
semiconductor nanoparticles having respective different central
emission wavelengths in the range 520-700 nm, the conversion layer
characterized by having an optical density between 0.07 and 2.5 at
405 nm and an absorption ratio of absorbance at 405 nm to a maximum
value of absorbance in the range 520-700 nm greater than 3:1,
wherein the conversion layer may be used to convert at least part
of the light of the first wavelength into light of other
wavelengths longer than the first wavelength.
36. A lighting device comprising the optical conversion layer of
claim 1.
37. A lighting device comprising the optical conversion layer of
claim 1.
38. A lighting device comprising the optical conversion layer of
claim 35.
39. The lighting device of claim 36, wherein the conversion layer
is adapted to pass through an unconverted part of the source light
of a first wavelength.
40. A lighting device comprising: a) a light source which emits
source light of a first wavelength; and b) a conversion layer
configured according to claim 1, said conversion layer being used
to convert at least part of light of the first wavelength into
light of a second wavelength longer than the first wavelength.
41. The lighting device of claim 40, wherein the nanoparticles are
seeded nanoparticles.
42. The lighting device of claim 41, wherein the seeded
nanoparticles are nanorod seeded particles.
43. The lighting device of claim 40, wherein the light source is at
least one light emitting diode and wherein the conversion layer
enhances the lighting device light output to provide one of the
following: white light with one of the following conditions: (1) a
CCT<10000K and with a CRI>70; and (2) white light with a
CCT<4500K and with a CRI>80.
44. (canceled)
45. A lighting device comprising: a) a light source which emits
source light of a first wavelength; and b) a conversion layer
configured according to claim 19, the conversion layer being used
to convert at least part of light of the first wavelength into
light of a second wavelength longer than the first wavelength.
46. The lighting device of claim 45, wherein the nanoparticles are
seeded nanoparticles.
47. The lighting device of claim 46, wherein the seeded
nanoparticles are nanorod seeded particles.
48. The lighting device of claim 45, wherein the light source is at
least one light emitting diode (LED) and wherein the conversion
layer enhances the lighting device light output to provide one of
the following: (1) white light with a CCT<10000K and with a
CRI>70; and (2) white light with a CCT<4500K and with a
CRI>80.
49. (canceled)
50. A lighting device comprising: a) a light source which emits
source light of a first wavelength; and b) the conversion layer
configured according to claim 35, the conversion layer being used
to convert at least part of light of the first wavelength into
light into other wavelengths longer than the first wavelength.
51. The lighting device of claim 50, wherein the nanoparticles are
seeded nanoparticles.
52. The lighting device of claim 51, wherein the seeded
nanoparticles are nanorod seeded particles.
53. The lighting device of claim 50, wherein the light source is at
least one light emitting diode and wherein the conversion layer
enhances the lighting device light output to provide one of the
following: (1) white light with a CCT<10000K and with a
CRI>70; (2) white light with a CCT<4500K and with a
CRI>80.
54. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Applications No. 61/299,012 filed Jan. 28, 2010 and titled
"Light source with prescribed colour emission" and 61/299,018 filed
Jan. 28, 2010 and titled "Phosphor-nanoparticle combination", both
of which are incorporated herein by reference in its entirety.
FIELD AND BACKGROUND
[0002] Embodiments of the invention relate in general to optical
devices which comprise semiconductor nanoparticles and in
particular to lighting devices which include conversion layers
having semiconductor quantum confined nanoparticles.
[0003] Light emitting diodes (LED) offer significant advantages
over incandescent and fluorescent lamps with respect to their high
energy efficiency and long lifetimes. LEDs are applicable in
diverse applications including displays, automobile and signage
lighting and domestic and street lighting.
[0004] A LED can emit monochromatic light in different regions of
the spectrum, depending on the inorganic semiconductor compound
used to fabricate it. However, "white" light, which is required for
a very large portion of the lighting industry, cannot be generated
using a conventional LED. Current solutions of producing white
light include the use of three or more LEDs with various colours
(e.g. Red, Green and Blue or "RGB"), or the use of a colour
conversion layer of phosphor material (e.g. Cerium:YAG) to generate
a broad white spectral emission from the ultraviolet (UV) or blue
emission of a LED. However, such white light is almost always
non-ideal and has in many cases undesired or unpleasant
characteristics which may require improvement or correction.
[0005] Colloidal based semiconductor quantum dots (QD) offer the
possibility of obtaining a colour gamut similar to and even better
than the one obtained with the multi-LED solution, using the
narrow-band emission of a QD tunable by size. Conversion layers
incorporating ODs are known, see e.g. U.S. Pat. Nos. 7,264,527 and
7,645,397 and US patent applications 2008/0173886 and 2009/0162011.
However, conversion layers based on QDs have challenges. These
include for example losses due to re-absorption effects, whereby
the QD emission is reabsorbed by other QDs in the layer. Generally
this will occur for a red QD absorbing the emission emanating from
QDs which emit more to the blue. This undesired process leads to
reduced energy efficiency of a regular QD conversion layer and also
to changes in the colour composition. The inherent size
distribution of QD samples already provides different colours
around a central colour. Therefore, re-absorption will take place
inherently within such a layer. In devices where phosphor is used
as part of a light conversion scheme to produce green light, the QD
layers will absorb partially the light from the phosphor as well,
leading to both re-absorption losses and colour changes.
[0006] In some cases, a close-packed conversion layer is desired.
Close-packed QD conversion layers suffer from the phenomenon known
as Fluorescence Resonant Energy Transfer (FRET), see e.g. Joseph R.
Lakowicz, "Principles of Fluorescence Spectroscopy", 2.sup.nd
edition, Kluwer Academic/Plenum Publishers, New York, 1999, pp.
367-443. FRET occurs between a donor QD which emits at a shorter
(e.g. bluer) wavelength relative to an acceptor QD positioned in
close proximity and which emits at longer wavelength. There is a
dipole-dipole interaction between the donor emission transition
dipole moment and the acceptor absorption transition dipole moment.
The efficiency of the FRET process depends on the spectral overlap
of the absorption of the donor with the emission of the acceptor.
The FRET distance between quantum dots is typically 10 nm or
smaller. The efficiency of the FRET process is very sensitive to
distance. FRET leads to colour change (red shift) and losses in the
efficiency of light conversion.
[0007] Core/shell nanoparticles (NPs) are known. These are discrete
nanoparticles characterized by a heterostructure in which a "core"
of one type of material is covered by a "shell" of another
material. In some cases, the shell is grown over the core which
serves as a "seed", the core/shell NP known then as a "seeded" NP
or SNP. The term "seed" or "core" refers to the innermost
semiconductor material contained in the heterostructure. FIG. 1
show schematic illustrations of known core/shell particles. FIG. 1A
illustrates a QD in which a substantially spherical shell coats a
symmetrically located and similarly spherical core. FIG. 1B
illustrates a rod shaped ("nanorod") SNP (RSNP) which has a core
located asymmetrically within an elongated shell. The term nanorod
refers to a nanocrystal having a rod-like shape, i.e. a nanocrystal
formed by extended growth along a first ("length") axis of the
crystal with very small dimensions maintained along the other two
axes. A nanorod has a very small (typically less than 10 nm)
diameter and a length which may range from about 6 nm to about 500
nm.
[0008] Typically the core has a nearly spherical shape. However,
cores of various shapes such as pseudo-pyramid, cube-octahedron and
others can be used. Typical core diameters range from about 1 nm to
about 20 nm. FIG. 1C illustrates a QD in which a substantially
spherical shell coats a symmetrically located and similarly
spherical core. The overall particle diameter is d.sub.2, much
larger than the core diameter d.sub.1. The magnitude of d.sub.2
compared with d.sub.1 affects the optical absorbance of the
core/shell NP.
[0009] As known, a SNP may include additional external shells which
can provide better optical and chemical properties such as higher
quantum yield (QY) and better durability. The combination may be
tuned to provide emitting colours as required for the application.
The length of the first shell can range in general between 10 nm
and 200 nm and in particular between 15 nm and 160 nm. The
thicknesses of the first shell in the other two dimensions (radial
axis of the rod shape) may range between 1 nm and 10 nm. The
thickness of additional shells may range in general between 0.3 nm
to 20 nm and in particular between 0.5 nm to 10 nm.
[0010] In view of the numerous deficiencies of QD conversion layers
mentioned above, there is a need for and it would be advantageous
to have conversion layers which do not suffer from such
deficiencies. In particular, there is a need for and it would be
advantageous to have nanoparticle-based thin conversion layers with
negligible re-absorption (of both same and different colour),
negligible clustering and high-loading effects and negligible
FRET.
Definitions
[0011] The term "core material" to the semiconductor material from
which the core is made. The material may be II-VI, III-V, IV-VI, or
I-III-VI.sub.2 semiconductors or combinations thereof. For example,
the seed/core material may be selected from CdS, CdSe, CdTe, ZnS,
ZnSe, ZnTe, ZnO, GaAs, GaP, GaAs, GaSb, HgS, HgSe, HgTe, InAs, InP,
InSb, AlAs, AlP, AlSb, Cu.sub.2S, Cu.sub.2Se, CuInS.sub.2,
CuInSe.sub.2, Cu.sub.2(ZnSn)S.sub.4, Cu.sub.2(InGa)S.sub.4, alloys
thereof, and mixtures thereof.
[0012] The term "shell material" refers to the semiconductor
material from which each of the non-spherical elongated shells is
made. The material may be a II-VI, III-V IV-VI, or I-III-VI.sub.2
semiconductor or combinations thereof. For example, the shell
material may be selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe,
ZnO, GaAs, GaP, GaAs, GaSb, GaN, HgS, HgSe, HgTe, InAs, InP, InSb,
AlAs, AlP, AlSb, Cu.sub.2S, Cu.sub.2Se, CuInS.sub.2, CuInSe.sub.2,
Cu.sub.2(ZnSn)S.sub.4, Cu.sub.2(InGa)S.sub.4, alloys thereof, and
mixtures thereof.
[0013] The term "host matrix" refers to a material which
incorporates the SNPs or other suitable nanoparticles. The host
matrix may be a polymer (formed from liquid or semisolid precursor
material such as monomer), an epoxy, silicone, glass or a hybrid of
silicone and epoxy. Specific (but not limiting) examples of
polymers include fluorinated polymers, polymers of ployacrylamide,
polymers of polyacrylic acids, polymers of polyacrylonitrile,
polymers of polyaniline, polymers of polybenzophenon, polymers of
poly(methyl mathacrylate), silicone polymers, aluminium polymers,
polymers of polybisphenol, polymers of polybutadiene, polymers of
polydimethylsiloxane, polymers of polyethylene, polymers of
polyisobutylene, polymers of polypropylene, polymers of polystyrene
and polyvinyl polymers, polyvinyl-butyral polymers or
perfluorocyclobutyl polymers.
[0014] The term "ligand" refers to an outer surface coating of the
nanoparticles. The coating passivates the SNP to prevent
agglomeration or aggregation to overcome the van der Waals binding
force between the nanoparticles. Ligands in common use: phosphines
and phosphine oxides such as trioctylphosphine oxide (TOPO),
trioctylphosphine (TOP), tributylphosphine (TBP), phosphonic acids
such as dodecylphosphonic acid (DDPA), tridecylphosphonic acid
(TDPA), octadecylphosphonic acid (ODPA) or hexylphosphonic acid
(HPA), amines such as dodecyl amine (DDA), tetradecyl amine (TDA),
hexadecyl amine (HDA) or octadecyl amine (ODA), thiols such as
hexadecane thiol or hexane thiol, mercapto carboxylic acids such as
mercapto propionic acid or mercapto undecanoic acid and other acids
such as myristic or palmitic acid.
SUMMARY
[0015] Embodiments of the invention disclose optical conversion
layers (or simply "layers") incorporating at least one SNP species
and/or other nanoparticles that have the needed characteristics
rendering this layer with its unique optical properties. One such
layer according to an embodiment of the invention is referred to
henceforth as a "SNP conversion layer" or simply "SNP layer".
References will be made henceforth also to "SNP sub-layers"
representing part of a SNP layer, and to SNP multilayers,
representing a structure with a plurality of SNP layers. Similar
terms will be used for RSNP based layers with "SNP" replaced by
"RSNP". To clarify, henceforth in this description, "layer" is
equivalent to "conversion layer". Embodiments of the invention
further disclose the application of SNP conversion layers for
transforming light, particularly for conversion of LED
monochromatic emission of short wavelength (e.g. blue or UV) to
longer wavelengths in the VIS/NIR range to produce light of
different colours. In particular, SNP layers of the invention may
be used with one or more LEDs to provide a white light device with
high energy efficiency and good optical properties such as high CRI
(Colour Rendering Index) and desired CCT (correlated colour
temperature). In other lighting applications, a SNP layer can
provide a necessary and beneficial spectral output such as large
gamut coverage, or specific colour bands.
[0016] In an embodiment, a SNP layer may include one type (species)
of SNP emitting essentially at a single colour. In another
embodiment, a SNP layer may include a mixture of several types of
SNPs emitting at different colours. In some embodiments, a SNP
layer may include SNPs incorporated in a host matrix, with or
without ligands. A SNP layered structure may comprise several
sub-layers, each of which may include a mixture of SNPs, or may
include a different type of SNP.
[0017] In some embodiments, the SNP layer thickness may be equal to
or thinner than 200 .mu.m. In some embodiments, the SNP layer
thickness may be equal to or thinner than 50 .mu.m. In some
embodiments, the SNP layer thickness may be equal to or thinner
than 2 .mu.m. In other embodiments, the SNP layer may have a
thickness ranging between ca. 50 and 1000 nm.
[0018] In some embodiments, a SNP layer may include SNPs having a
high-loading ratio within a polymer matrix, epoxy or resin. In some
embodiments, the high-loading ratio may be up to 40%. In some
embodiments, the high-loading ratio may be up to 80%. In some
embodiments, the high-loading ratio may be up to 100%.
[0019] SNP conversion layers according to embodiments disclosed
herein provide functionalities and advantageous properties which
are unknown in QD conversion layers and which were not previously
discovered. These include:
[0020] 1) Negligible re-absorption (both same colour and different
colour). The re-absorption in a SNP conversion layer is reduced
significantly (in comparison to that in a QD conversion layer)
because of low red absorbance. In general, re-absorption leads to
loss of energy. For example, assume a typical QY of 0.8. In a
single re-absorption event, the OY is reduced to
0.8.times.0.8=0.64. In two such events, the QY is reduced further
to 0.8.sup.3=0.51. This loss is avoided in a SNP conversion layer.
Hence, the efficiency is improved. Re-absorption also leads to a
red shift, which is also avoided in such a SNP conversion layer.
The aspect of negligible re-absorption is present not only for one
colour on itself (e.g. red to more red), but also in green emitting
SNPs or phosphors. Namely, with a QD conversion layer, red QDs will
reabsorb green emission, leading to reduced efficiency and colour
shift. With a SNP conversion layer, this re-absorption is
minimized. Both same colour and different colour re-absorption
avoidance functions are unique features of SNP layers, whether
densely-packed or not.
[0021] 2) Very efficient "funneling" of energy from blue excitation
to red emission. An SNP conversion layer acts essentially as an
"optical antenna" in the spectral sense. It performs this task much
more efficiently that a regular QD conversion layer, since it has
very high absorbance in the blue and strong red photoluminescence
(PL) accompanied by minimal red re-absorption, see point (1)
above.
[0022] 3): FRET avoidance or minimalization. In a regular QD
conversion layer, The typical length scale of FRET is .about.10 nm,
with 1/R.sup.6 dependence, where R is the distance between two QD
particles. For example, if the initial emission QY is 0.8, the QY
is reduced to 0.64 after a single FRET process. FRET also leads to
red shift, which is avoided in a SNP layer. A densely-packed SNP
conversion layer (with small distances between the SNPs, e.g. 0-50
nm) owing to their unique characteristics will avoid the losses and
deficiencies related to FRET commonly encountered in densely-packed
QD layers. Exemplarily, "densely-packed" as applied to SNPs in
conversion layers of the invention may include .about.85% SNPs and
.about.15% ligands dispersed in a host matrix.
[0023] In an embodiment, a SNP layer may be coated on an optical
device such as a LED to improve its emission spectrum. In another
embodiment, a separate SNP layer may be positioned in the optical
path of light emitted by one or more LEDs for the same purpose. In
yet another embodiment, a layered SNP structure comprising a
plurality of different SNP conversion sub-layers may be coated on a
LED. In yet another embodiment, the layered SNP structure may be
positioned in the optical path of light emitted by LEDs. In some
embodiments, a SNP layer may be spaced apart from a LED by a
coupling layer which may be an air gap, an optical filter such as
short wavelength (UV, blue) pass filter, a long wavelength (e.g.
green or red) reflection filter, or an index matching layer which
minimizes energy loss by reflection. The spacing between the LED
and the SNP layer can for example be used to minimize heating due
to heat flow from the LED to the SNP layer.
[0024] A combination of a LED and a SNP conversion layer or layered
structure may be used in a lighting device (i.e. a domestic light,
a signage light, a vehicle light, a portable light, a back light or
any other light). In some embodiments, a lighting device may
further comprise an optical element such as a lens, a waveguide, a
scatterer, a reflective element, a refractive element or a
diffractive element. The optical element may be placed between the
SNP layer and the light source or before the SNP layer in the
optical path, or on the sides of the layer (for example a
reflective element for using scattered light). In some embodiments,
the lighting device may include a combination of two or more
optical elements from the list above in addition to a LED and one
or more SNP layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Non-limiting embodiments of the invention are herein
described, by way of example only, with reference to the
accompanying drawings, wherein:
[0026] FIG. 1 is a schematic illustration of known core/shell
particles: (A) core QD/shell QD; (B) RSNP; (C) SNP;
[0027] FIG. 2 shows experimental results of optical absorption and
emission of a core/shell QD material vs. a RSNP material used in
embodiments of the invention: (A) for green light; (B) for orange
light;
[0028] FIG. 3 shows normalized absorption curves of three types of
red emitting SNPs having different lengths;
[0029] FIG. 4 illustrates schematically the FRET effect in
densely-packed QDs, in which it is efficient, and in densely-packed
RSNPs, in which it is blocked;
[0030] FIG. 5A shows schematically a light conversion device which
includes a SNP layer according to one embodiment of the
invention;
[0031] FIG. 5B shows schematically a light conversion device which
includes a SNP layer according to another embodiment of the
invention;
[0032] FIG. 6A shows schematically a light conversion device which
includes a SNP layer according to yet another embodiment of the
invention;
[0033] FIG. 6B shows schematically a light conversion device which
includes a SNP layer according to yet another embodiment of the
invention;
[0034] FIG. 7 shows schematically a lighting device which includes
a SNP layer according to an embodiment of the invention;
[0035] FIG. 8 shows schematically a lighting device which includes
a SNP layer according to another embodiment of the invention;
[0036] FIG. 9 shows schematically a lighting device which includes
a SNP layer according to yet another embodiment of the
invention.
[0037] FIG. 10A shows a LED coupled to a waveguide that has an SNP
layer embedded therewithin;
[0038] FIG. 10B shows schematically a LED coupled to a waveguide
that has an SNP layer positioned on a top surface thereof;
[0039] FIG. 11 shows the absorption (dotted line) and the PL (full
line) of a conversion layer which comprises 33.times.7 nm CdSe/CdS
RSNPs embedded in polymer PVB film;
[0040] FIG. 12A shows the light spectrum of a lighting device
comprising a 455 nm blue LED with a conversion layer which
comprises 33.times.7 nm CdSe/CdS RSNPs embedded in a PVB film with
added BaSO.sub.4 particles;
[0041] FIG. 12B shows the light spectrum of a lighting device
comprising a 455 nm blue LED with a conversion layer which
comprises 27.times.5.5 nm CdSe/CdS RSNPs embedded in a Silicone RTV
film;
[0042] FIG. 13A shows the absorption (dotted line) and the PL
spectra (full line) of a dense spin coated red emitting RSNP layer
on glass;
[0043] FIG. 13B shows the absorption (dotted line) and the PL
spectra (full line) of a dense spin coated green emitting RSNP
layer on glass;
[0044] FIG. 14A shows the normalized light spectrum of a lighting
device comprising a broad band LED based element with a SNP
conversion layer.
[0045] FIG. 14B shows the normalized light spectrum of a lighting
device comprising a broad band LED based element with another SNP
conversion layer.
[0046] FIG. 15 shows a CIE chart with the two outputs of FIGS. 14A,
B marked as shown.
[0047] FIG. 16 shows the absorption (dotted line) and the PL
spectra (full line) of the SNP film of Example 7.
DETAILED DESCRIPTION
[0048] Embodiments of SNP layers, SNP layers used to condition LED
light and lighting devices including such layers are now described
in more detail. In particular, advantageous properties and features
of such layers are described next with reference to FIGS. 2-4. The
various SNP layers mentioned below may be prepared using procedures
detailed in Examples below.
[0049] Reference is now made to FIGS. 2A, B, which show a
comparison between the absorption and emission of a known
conventional CdSe/ZnS core/shell QD layer and two types of RSNP
layers according to embodiments of the invention: a green emitting
RSNP layer (FIG. 2A) and an orange emitting RSNP layer (FIG. 2B).
The comparison is between the absorption and normalized emission of
the QD layer vs. the SNP layers having a matched absorption at the
excitation wavelength of 450 nm. The Green RSNP layer included
CdSe/CdS core/shell RSNPs with dimensions 4.times.27 nm (diameter x
length), emitting at a center wavelength (CWL) or peak wavelength
of 540 nm with a full width half maximum (FWHM) of 29 nm,. The
Orange RSNP layer included CdSe/CdS RSNPs with dimensions
5.times.40 nm, a CWL at 600 nm and FWHM of 28 nm. Both Orange and
Green emitting layers were prepared in a similar way, and both were
190 .mu.m-thick, with diameter of 42 mm.
[0050] The PL quantum yield (QY) of both QD and RSNP nanoparticles
was similar and on the order of 50%. This is a typical value. In
other prepared samples, the QY ranged from 5-100%, more often
between 20-90% and even more often between 50-80%. The absorption
is measured in relative optical density (OD) units, where the scale
shown is normalized to the range [0 1] for convenience.
Significantly, for the green light emitting layers in FIG. 2A, the
OD of the QD layer in the emission wavelength range (e.g. 520-550
nm) is 10 times higher than that of the RSNP layer (0.64 vs.
0.065). The OD difference for the orange emitting layers in FIG. 2B
is even higher (0.575 vs. 0.037, a factor of .about.15). In other
examples (not shown), the OD in the emission range of a QD layer
was found to be 3-30 times higher than that of a RSNP layer.
Therefore, losses due to self-absorbance are significant for the QD
layer case and negligible for the RSNP layer case. This property is
used in various SNP layers of the invention (whether densely-packed
or not) to provide far superior products over existing layers based
on quantum dots.
[0051] The inventors have further determined that SNP layers of the
invention have a feature of very efficient "funneling" of energy
from blue excitation to red emission. An SNP layer acts essentially
as an "optical antenna" in the spectral sense. It performs this
task much more efficiently that a regular QD layer, since it has
very high absorbance in the blue and strong red PL accompanied by
minimal red re-absorption, see FIG. 3.
[0052] FIG. 3 shows normalized absorption curves of three types of
RSNP layers prepared as described in Example 1 below and comprising
in each case red emitting RSNPs (CdSe/CdS) having different overall
dimensions and nearly similar emission spectra: a curve 300 for
5.8.times.16 nm RSNPs with 622 nm emission, a curve 302 for
4.5.times.45 nm RSNPs with 625 nm emission and a curve 304 for
4.5.times.95 nm RSNPs with 628 nm emission. These curves illustrate
the funneling effect in different conversion layers. The absorption
curves are normalized to OD 1 at 455 nm. The "absorption ratio"
between absorption at 455 nm to that at the emission wavelengths is
respectively 1:5, 1:12 and 1:23 for SNP layers with RSNPs of
lengths 16, 45 and 95 nm. This shows that the funneling is more
efficient for layers comprising longer RSNPs and that the
absorption ratio is "tunable" by varying the RSNP length. Note that
for SNPs which are not rod-shaped, a similar tuning can be achieved
by increasing the shell to core diameter ratio. This tunability is
very useful in SNP layers since it allows the SNP layers to act as
the efficient spectral antenna to convert blue light to red light
desired in a light source and application. An additional parameter
resulting from this special characteristic of SNP layer is that it
allows to efficiently balance the light between the different
spectral regions of the visible spectrum (say green-yellow emitted
by CE:YAG and the red emitted by SNPs) to obtain light with
required characteristic (such as CCT and CRI).
[0053] The inventors have further determined that layers with
densely-packed SNPs have significantly smaller FRET losses than
layers having densely-packed QDs. FIG. 4 illustrates schematically
the FRET effect in densely-packed conversion layers of QDs and
RSNPs. FIG. 4A, for the QD conversion layer case, shows some QDs
acting as donors (D, 410) and some acting as acceptors (A, 420),
with a typical distance between donor and acceptor denoted by the
arrow 430. In such a typical QD conversion layer, the smaller QDs
act as donors to larger QDs which act as acceptors. The typical
center-to-center distance is on the order of the FRET distance of
.about.10 nm, hence FRET is efficient in such a densely-packed QD
conversion layer. FIG. 4B, for the SNP layer case, shows that the
special geometry induces on average large distances between a RSNP
440 emitting a colour slightly bluer as compared to another RSNP
450. The typical core-to-core distance in this case (indicated by
460) is around half of the RSNP length, and is engineered to exceed
the FRET distance, leading to a significantly reduced probability
for FRET processes.
[0054] To reiterate, known QDs do not provide such a large distance
and consequently, in a densely-packed layer arrangement, their FRET
losses are inherent, leading to reduced conversion efficiency. In
addition, in a densely-packed QD conversion layer, the FRET process
leads to a red shift of the emission. In contrast, in a SNP layer
as disclosed herein, the emission is maintained at the tailored and
desired wavelength, providing the required colour and higher energy
efficiency.
[0055] To reemphasize, the optical properties of the SNP layers of
the invention provide significant advantages over existing QD
conversion layers due to low re-absorption and small energy
transfer losses and light colour changes. The capability to
minimize re-absorption implies that higher absorption (by longer
optical paths and/or higher concentration of the SNP) may be used.
As a result, significant absorption of the blue or UV LED light may
be achieved and higher efficiency devices are enabled, exemplified
by the spectral antenna characteristic of the SNP conversion layers
disclosed herein.
[0056] In known QD conversion layers, the formation of clusters of
QD material may lead to energy losses via FRET, as described above.
Clustering can occur even at low loading, while high loading can
occur without dense packing (the latter correlated with extremely
high loading). Since QDs are densely-packed in a cluster, the
distance between neighbouring QDs is small and energy transfer
processes may become significant. These will reduce the emission
output and the efficiency of the devices and will also affect the
light colour output. SNP clustering in a conversion layer does not
lead to energy transfer losses, and therefore losses in efficiency
or changes in the light colour output are avoided. Therefore,
devices based on SNP will function even if clusters are formed.
This enables the use of thinner layers.
[0057] Known QD materials for light conversion are embedded in a
host material (matrix) in a low-loading ratio to avoid losses by
mechanisms such as by FRET. As a result, a QD conversion layer must
be thick (typically thicker than 100 .mu.m in most cases), yet
still contain sufficient amount of material to achieve effective
absorption of blue light for conversion, thereby inherently leading
to re-absorption losses. In addition, for thick layers,
manufacturing methods become less accurate and more resource
consuming In sharp contrast, high-loading ratio SNP layers may be
made very thin. For example, thin SNP layers may be produced using
spin-coating deposition techniques, see Examples 4 and 5 in which
the layers are respectively 510 nm and 230 nm-thick. In general,
for SNP/RSNP conversion layers of the invention, absorption and
emission can be controlled to provide tailored colour and optical
characteristics, power and efficiency. Densely-packed, high-loading
thin SNP layers have an additional advantage in that they may be
made with excellent uniformity over large length scales, from a few
millimetres to centimetres and even more.
[0058] High-loading ratio SNP layers may be prepared using a
polymer, epoxy or resin matrix, or simply by having a layer of
close-packed SNPs. The polymer or additive may serve additional
purposes such as for encapsulating the optically active
nanoparticles to prevent oxidation or photo-degradation, serve as a
medium easy for mechanical integration in the lighting device and
as a medium which can also enhance the light extraction from the
layer due to its refractive index and surface roughness. A host
material (matrix) can also serve as a matrix for diffusive
particles such as SiO.sub.2, Al, BaSO.sub.4 or TiO.sub.2, which can
enhance the scattering within the layer. The loading ratio may be
used to control the refractive index of the SNP layer. Layers of
low-loading ratio may have a refractive index as low as 1.5 and
even lower, while layers with a high-loading ratio may have a
refractive index of 1.8 and even higher. Typically, for polymers
with a refractive index of 1.3-1.5, the refractive index will not
change up to .about.15% loading ratio. Typically, with ligands, the
refractive index may be 1.8 and more.
[0059] Tables 1-3 summarize various exemplary embodiments of
SNP/RSNP conversion layers made according to the invention. Other
embodiments of conversion layers having advantageous physical
parameters and optical performance are possible and can be made
according to the teachings disclosed herein. Therefore, these
exemplary embodiments should not be considered as limiting the
invention in any way.
TABLE-US-00001 TABLE 1 Parameters for Red-emitting RSNP conversion
layers PL SNP Layer Red Conversion Embedding length Emission
Thickness Shift.sup.d layer/RSNP type material [nm] [nm] [.mu.m]
AR.sup.a.sub.red AR.sup.b.sub.green OD.sup.c [nm] CdSe\CdS
Ligands.sup.e 8-150 580-680 0.1-2 For RSNP For RSNP 0.07- <5
ZnSe\CdS length length 2.0 CdSe\CdS\ZnS 8-100 nm, 8-110 nm,
CdSe\CdZnS AR > 3.5:1 AR > 2.5:1 CdSe\CdZnS\ZnS For RSNP For
RSNP length length 60- 60- 150 nm, 100 nm, AR > 7:1 AR > 6:1
CdSe\CdS Polymer.sup.f 8-150 580-680 1-5000 For SNP For RSNP 0.07-
<5 ZnSe\CdS or length length 2.0 CdSe\CdS\ZnS Silicone.sup.g
8-100 nm, 8-110 nm, CdSe\CdZnS AR > 3.5:1 AR > 2.5:1
CdSe\CdZnS\ZnS For RSNP For RSNP length length 60-150 60-100 nm,
nm. AR > 7:1 AR > 6:1 Markings in Table 1: .sup.aAR.sub.red
is the ratio between the absorbance at 455 nm to the maximal
absorbance in a wavelength range between 580-700 nm, i.e.
AR.sub.red = (Absorbance.sub.455 nm/max(Absorbance.sub.580-700 nm);
.sup.bAR.sub.green is the ratio between the absorbance at 455 nm to
the maximal absorbance in a wavelength range between 520-580 nm,
i.e. AR.sub.green = (Absorbance.sub.455
nm/max(Absorbance.sub.520-580 nm); .sup.cOD is measured at 455 nm;
.sup.dPL Red shift is the difference in nanometers between the CWL
measured in Toluene at low OD (<0.1) and the CWL measured for
the sample; .sup.eLigands can be selected from list given in
definitions; .sup.fThe polymer can be selected from list given in
definitions; .sup.gSilicone with suitable optical and mechanical
properties can be selected from various commercial suppliers.
TABLE-US-00002 TABLE 2 Parameters for Green-emitting RSNP
conversion layers PL SNP Layer Red Conversion Embedding length
Emission Thickness Shift.sup.c layer/RSNP type material [nm] [nm]
[.mu.m] AR.sup.a.sub.green OD.sup.b [nm] CdSe\CdS Ligands.sup.d
8-150 520-580 0.1-5 For RSNP length 0.07- <5 ZnSe\CdS 8-100 nm,
2.0 CdSe\CdS\ZnS AR > 3.5:1 CdSe\CdZnS For RSNP length
CdSe\CdZnS\ZnS 45:150 AR > 7:1 CdSe\CdS Polymer.sup.e 8-150
520-580 1-10 For RSNP length 0.05- <5 ZnSe\CdS or 8-100 nm, 2.0
CdSe\CdS\ZnS Silicone.sup.f AR > 3.5:1 CdSe\CdZnS For RSNP
length CdSe\CdZnS\ZnS 45:150, AR > 7:1 Markings in Table 2:
.sup.aAR.sub.green is the ratio between the absorbance at 455 nm to
the maximal absorbance in a wavelength range between 520-580 nm,
i.e. AR.sub.green = (Absorbance.sub.405
nm/max(Absorbance.sub.520-580 nm); .sup.bOD is measured at 405 nm;
.sup.cPL Red shift is the difference in nanometers between the CWL
measured in Toluene at low OD (<0.1) and the CWL measured for
the sample; .sup.dLigands can be selected from list given in
definitions; .sup.eThe polymer can be selected from list given in
definitions; .sup.fSilicone with suitable optical and mechanical
properties can be selected from various commercial suppliers.
TABLE-US-00003 TABLE 3 Parameters for Green-and Red-emitting SNP
conversion layers Layer PL Red Conversion layer/ Embedding Emission
Thickness Shift.sup.d SNP type material [nm] [.mu.m]
AR.sup.a.sub.green AR.sup.b.sub.red OD.sup.c [nm] CdSe\CdS
Ligands.sup.e 580- 0.1-5 AR > 3:1 0.07- <5 ZnSe\CdS 680 2.0
CdSe\CdS\ZnS CdSe\CdZnS CdSe\CdZnS\ZnS CdSe\CdS Polymer.sup.f 580-
1-10 AR > 3:1 0.05- <5 ZnSe\CdS or 680 2.0 CdSe\CdS\ZnS
Silicone.sup.g CdSe\CdZnS CdSe\CdZnS\ZnS CdSe\CdS Ligands.sup.e
520- 0.1-5 AR > 3:1 0.07- <5 ZnSe\CdS 580 2.0 CdSe\CdS\ZnS
CdSe\CdZnS CdSe\CdZnS\ZnS CdSe\CdS Polymer.sup.f 520- 1-10 AR >
3:1 0.05- <5 ZnSe\CdS or 580 2.0 CdSe\CdS\ZnS Silicone.sup.g
CdSe\CdZnS CdSe\CdZnS\ZnS Markings in Table 3: .sup.aAR.sub.green
is the ratio between the absorbance at 405 nm to the maximal
absorbance in a wavelength range between 520-580 nm, i.e.
AR.sub.green = (Absorbance.sub.405 nm/max(Absorbance.sub.520-580
nm), .sup.bAR.sub.red is the ratio between the absorbance at 455 nm
to the maximal absorbance in a wavelength range between 580-680 nm,
i.e. AR.sub.red = (Absorbance.sub.455 nm/max(Absorbance.sub.580-680
nm); .sup.cOD is measured at 455 nm for nanoparticles emitting at
580-680 nm and at 405 nm for nanoparticles emitting at 520-580 nm;
.sup.dPL Red shift is the difference in nanometers between the CWL
measured in Toluene at low OD (<0.1) and the CWL measured for
the sample; .sup.eLigands can be selected from list given in
definitions; .sup.fThe polymer can be selected from list given in
definitions; .sup.gSilicone with suitable optical and mechanical
properties can be selected from various commercial suppliers.
[0060] FIG. 5A shows schematically a lighting device 500a which
includes a SNP layer 502a according to one embodiment of the
invention. Light produced by a suitable source 504a (exemplarily a
LED emitting UV light) is directed at SNP layer 502a. Layer 502a
comprises SNPs that convert the light from blue and/or UV to longer
wavelengths. Different populations (types) of SNPs (having
different cores or shell sizes or materials) will emit different
colours. The colours emitted by the SNP layer may be combined with
the light produced by source 504a or used independently to form
different light combinations. In order to improve and tune the
spectral properties of the emission, more than one type of SNPs can
be used, e.g. mixtures of blue, green and red emitting SNPs (their
light exemplarily marked RGB). The various colours may be chosen so
as to provide white light. Other colour combinations, as desired
for a specific lighting application, can be generated by tailoring
the SNP conversion layer.
[0061] FIG. 5B shows schematically a lighting device 500b which
includes a SNP layer 502a according to another embodiment of the
invention. In this embodiment, light produced by a suitable source
504b (exemplarily a LED emitting blue light) remains partially
un-converted (i.e. passes through unaffected) by a SNP layer 502b.
Layer 502b incorporates SNPs that convert the light from blue and
shorter wavelengths to green and red. Layer 502b further
incorporates diffusive structures or particles that spread and mix
the unabsorbed light in a tailored pattern, to conform with the
spatial and optical characteristics of the photoluminescence of the
SNPs incorporated therein. That is, these structures scatter both
the incoming blue light and the SNP-emitted light such that the
combined light has the same angular diversion when it exits the SNP
layer as a "white" light. In addition, the white has high quality
green and red light added to the LED blue light to provide a large
colour gamut for a display backlight.
[0062] FIG. 6A shows schematically a lighting device 600a which
includes a SNP layer 602a according to yet another embodiment of
the invention. In this embodiment, a "colour mixture light" source
604a is improved or corrected by SNP layer 602a. Layer 602a
includes a plurality of SNP species which may have different cores
or shell sizes, different materials and/or different spectral
properties. The SNPs act to convert the colour mixture light source
into an improved colour mixture light. In an embodiment, the
improved colour mixture light output from the lighting device can
be "white light" with a CCT in the range of 2500-6000K with high
CRI. In another embodiment, the improved colour mixture light can
be white light with a CCT in the range of 2700-4500K range with
high CRI. The source light may be white light with high CCT (for
example 5000-10000K). Alternatively, it may be a light combination
which cannot be defined as white light but which includes light in
the range of the visible spectrum. The improvement includes for
example addition of red light to the emission, thereby providing a
lower CCT and better CRI.
[0063] FIG. 6B shows schematically a light conversion device 600b
which includes a SNP layer 602b according to yet another embodiment
of the invention. In this embodiment, layer 602b includes, in
addition to a plurality of SNP species such as in layer 602a,
diffusive structures or particles that spread and mix the
un-absorbed light from source 604b in a tailored pattern to produce
a further improved colour mixture light.
[0064] In alternative embodiments, the lighting device can include
several SNP layers, each providing a separate function, may be used
instead of a single SNP layer. Scattering and controlling the
transmission characteristics (e.g. homogenization) of transmitted
and emitted light may be achieved by incorporating in one or more
of the SNP conversion layers either refractive particles such as
small SiO.sub.2 beads or reflective particles such as metal
particles or light diffusing particles such as BaSO.sub.4 and
TiO.sub.2 by adding a patterning (e.g. diffusive) layer, or by
patterning the surface of at least one of the layers.
[0065] FIG. 7 shows schematically a lighting device 700 which
includes a SNP conversion layer according to an embodiment of the
invention. Device 700 includes a blue or UV LED light source, an
optional spacer layer (or air as spacer) 704, a SNP conversion
layer 706, an optional encapsulation layer 708, an optional
transmissive optical element 710 for light extraction to desired
directionality, an optional refractive element such as a lens 712
to collimate or focus the light, and an optional reflective element
714 placed behind and around the LED element to collect and direct
emission from large angles to the correct output direction. In some
embodiments, the high refractive index of a SNP layer with a
high-loading ratio is preferred in order to increase the light
extraction from the LED chip.
[0066] FIG. 8 shows schematically a lighting device 800 which
includes a SNP layer according to another embodiment of the
invention. In device 800, an optical filter 806 is between a SNP
layer 802 and a LED emitting chip 804. Optical filter 806 is a
filter which transmits short wavelength 820 (e.g. blue or UV) light
and reflects longer wavelength (e.g. green or red) light 822,
thereby enabling light recycling and a more efficient device. While
the light recycling increases the optical path of the emitted light
in the SNP layer, due to the low self-absorbance, any extra loss
would be minimized. In contrast, with a QD layer, the extra loss
will be significant. Optical elements between the light source and
the SNP layer may also be used to shape or otherwise control the
light source characteristics. Like device 700, device 800 further
comprises an optional transmissive optical element 810 for light
extraction to desired directionality, an optional refractive
element such as a lens 812 to collimate or focus the light, and an
optional reflective element 814 placed behind and around the LED
element to collect and direct emission from large angles to the
correct output direction. Placing the SNP layer at a distance from
the LED element can diminish the light intensity at the SNP layer
and the temperature level thereby increasing its durability.
[0067] FIG. 9 shows schematically a lighting device 900 which
includes a SNP layer according to yet another embodiment of the
invention. Device 900 includes a SNP layer shaped to fit in a
curved optical element 902, serving to colour convert and also to
diffuse the light, a LED 904 and additional layers 906 used for
example for spatial patterning or optical filtering (e.g.
additional UV filtering). SNP layers can be thin yet efficient,
which represents a significant advantage over the performances of
thick QD conversion layers.
[0068] FIG. 10A shows a LED 1002a coupled to a waveguide assembly
1004a that has an SNP layer 1006a embedded therewithin. The
waveguide includes a reflecting layer at a bottom 1008a (which may
be diffusive or reflective, patterned or homogenous) and an
optional light extraction layer 1010a. FIG. 10B shows schematically
a LED 1002b coupled to a waveguide assembly 1004b that has an SNP
layer 1006b positioned on a top surface 1008 thereof and an
optional light extraction layer 1010b. In both embodiments, the SNP
layer is shown excited by light coming from emitted by the LED
through an edge 1012a or 1012b of the waveguide. As light
propagates in the waveguide, it passes through the SNP layer again
and again. Light converted in the SNP layer is then transmitted
across the waveguide over a relatively great distance, which can be
in the millimetres to centimetres to tens of centimetres range. In
this application, the low self-absorbance of the SNP layer may be
critical, since the light travels over a long optical path. The
reflective and/or diffusive optical elements (1008a, 1008b 1010a,
1010b and 1012b) may be placed at all areas of the device where the
light can be emitted not in the needed direction. These elements
will return the light into the waveguide and increase its
efficiency
EXAMPLES
Example 1
Lighting Device with RSNP Conversion Layer within Polymer Host
Providing Red Light
[0069] RSNPs were synthesized following similar procedures to those
described in L. Carbone et al. "Synthesis and Micrometer-Scale
Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth
Approach" Nano Letters, 2007, 7 (10), pp 2942-2950. In a first
step, CdSe cores with diameter of 3.8 nm were synthesized. In a
second step, red emitting CdSe/CdS RSNPs were synthesized using the
CdSe cores as seeds. The resulting RSNPs had dimensions of
33.times.7 nm with an emission maximum is at 635 nm with FWHM of 30
nm when measured in a Toluene solution.
[0070] A RSNP conversion layer was prepared as follows: 0.5 g of
Poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVB), a
resin usually used for applications that require strong binding,
optical clarity, adhesion to many surfaces, toughness and
flexibility and commercially available from Sigma-Aldrich (3 Plaut
St., Rabin Park, Rehovot 76100, Israel) were dissolved in 4 ml
Toluene. 12 mg of RSNPs were dissolved in 1 ml Toluene to form a
RSNP solution. The RSNP solution was added to the polymer mixture
while stirring. The mixture was transferred to a pattern vessel
which was inserted into a dessicator and vacuumed for 15 hours,
after which the mixture became solid. The resulting film thickness
was 190 .mu.m. The optical characteristics of the conversion layer
are presented in FIG. 11, which shows the absorption (dotted line)
and the PL (full line) spectra. The emission maximum is at 635 nm,
with a FWHM of 30 nm. The absorption OD is 1.18 at 455 nm, 0.07 at
540 nm and <0.046 at 600-750 nm, i.e. 25 times smaller than the
OD at 455 nm. This RSNP layer therefore funnels light from blue to
red emission.
[0071] The RSNP layer was incorporated in a lighting device similar
to that of FIG. 5A. In the lighting device, a UV LED at 360 nm was
used to illuminate the RSNP layer, providing light output in the
red, at 635 nm. Negligible UV output was detected, as the UV light
was absorbed and converted very effectively by the RSNP layer.
Example 2
Lighting Device with Diffusive RSNP Conversion Layer within Polymer
Host Providing Combination of Blue and Red Light
[0072] A diffusive RSNP layer was prepared using the procedure in
Example 1, with a modification that 1.3 mg of RSNP was dissolved in
1 ml Toluene and that after the 10 minutes stirring of RSNPs in
polymer, 5 mg of BaSO.sub.4 particles were added to the solution
and stirred for another 15 minutes. The resulting film had
diffusive properties that enhanced the optical emission and
increased the extraction of the light in a required direction.
[0073] The RSNP layer was incorporated in a lighting device as
shown in FIG. 5B. A blue LED emitting at 455 nm was used to
illuminate the RSNP layer. The lighting output was measured and the
light spectrum is presented in FIG. 12A, which shows a combination
of a blue remnant from the blue LED and a red component from the
RSNP conversion layer.
Example 3
Lighting Device with RSNP Conversion Layer within Silicone RTV
Providing Combination of Blue and Red Light
[0074] A RSNP layer in Silicone RTV was prepared as follows: 1 g of
RTV615A (Momentive, 22 Corporate Woods Boulevard, Albany, N.Y.
12211 USA) was stirred with 0.1 g of RTV615B for 10 min. 1.5 mg of
CdSe/CdS RSNPs with overall dimensions of 27.times.5.5 nm emitting
at 635 nm was dissolved in 250 .mu.l Toluene. The RSNP solution was
added to the silicone mixture while stirring, then vacuumed until
no bubbles remained. The solution was then deposited on a glass
substrate and sandwiched using another glass substrate. 600
.mu.m-thick spacers were positioned between the two glass
substrates to obtain the desired film thickness. The sandwiched
structure was then placed on a hot plate at 150.degree. C. for 15
minutes, after which the solution became solid. The measured film
thickness was 600 .mu.m.
[0075] The RSNP layer was incorporated in a lighting device as
shown in FIG. 5B. A blue LED emitting at 455 nm was used to
illuminate the RSNP layer. The lighting output was measured and the
light spectrum is presented in FIG. 12B, which shows a combination
of a blue remnant from the blue LED at 455 nm and a red component
from the RSNP layer at 635 nm with a FWHM of 30 nm.
Example 4
Lighting Device with Thin Dense Spin-Coated RSNP Conversion Layer
Providing Red Light
[0076] A dense RSNP layer was prepared as follows: first prepared
was a solution of 35.times.5.4 nm CdSe/CdS RSNPs, emitting at 635
nm, in Toluene with 1:4 weight/volume (mg/.mu.L) ratio. 20 .mu.L of
the solution was drop cast on a soda lime glass substrate and
spread by spin coating at 2000 rpm. The deposited film was measured
to have an absorbance OD of 0.51 at 455 nm, and OD of 0.9 at 360
nm. The thickness was 0.510 um as measured by a profilometer. FIG.
13A shows the absorption (dotted line) and the PL (full line)
spectra of this RSNP layer. The emission maximum is at 633 nm, with
a FWHM of 33 nm. The absorption OD is 0.96 at 360 nm, 0.5 at 455
nm, 0.035 at 540 nm and 0.025 at 600-750 nm, the latter 20 times
smaller than the OD at 455 nm.
[0077] The RSNP layer was incorporated in a lighting device as
shown in FIG. 5A A UV LED at 360 nm was used to illuminate the RSNP
layer, and provided light output in the red at 633 nm (not
shown).
Example 5
Lighting Device with Thin Dense Spin-Coated RSNP Conversion Layer
Providing Green Light
[0078] A dense RSNP layer was prepared as follows: A solution of
green emitting 20.times.3.5 nm CdSe/CdS RSNPs in Toluene with 1:5
weight/volume (mg/.mu.L) ratio was prepared. 20 .mu.L of solution
containing the RSNPs was drop cast on a soda lime glass substrate
and spread by spin coating at 2000 rpm. The deposited film was
measured to have an absorbance OD of 0.07 at 455 nm and a thickness
of 230 nm as measured by a profilometer. FIG. 13B shows the
absorption (dotted line) and the PL (full line) spectra of this
RSNP layer. The emission maximum is at 540, with a FWHM of 33 nm.
The absorption OD is 0.165 at 360 nm, and 0.008 at 540 nm, the
latter 20 times smaller than the OD at 360 nm.
[0079] The RSNP layer was incorporated in a lighting device as
shown in FIG. 5A. A UV LED at 360 nm was used to illuminate this
RSNP layer, and provided light output in the red, at 540 nm (not
shown).
Example 6
Lighting Devices with RSNP Conversion Layers Providing White
Light
[0080] Two RSNP layer samples were prepared using the methods
described above for PVB with scatterers (example 2) RSNP layer
CL14A had 10 mg of red emitting RSNPs and 25 mg of BaSO.sub.4,
inserted into 0.5 g of PVB. RSNP layer CL14B had 20 mg of red
emitting RSNP and 25 mg of BaSO.sub.4, inserted into 0.5 g of PVB.
Each of the two samples was 190 .mu.m-thick and had a diameter of
42 mm.
[0081] The RSNP layers were incorporated in two lighting devices as
shown in FIG. 6B. In both lighting devices, the RSNP layers were
placed at the aperture of a LED module composed of a blue LED
source and a specially prepared Ce:YAG based phosphor layer in a
silicone matrix. The light output was measured and is shown in
FIGS. 14A and B, for a lighting device with layers CL14A and CL14B,
respectively. The light seen is composed of contributions of blue
light from the 455 nm LED, a broad peak around 580 nm for the
Ce-YAG based phosphor and red light from the RSNP layer. The CIE
1931 coordinates were calculated and the location of the two
lighting devices on the CIE Chromaticity Diagram is shown in FIG.
15. The CCT for CL14A is 3420 K and for CL14B is 2730 K while the
CRI for CL14A is 95 and for CL14B is 92.
Example 7
Lighting Devices with SNP Conversion Layers Providing White
Light
[0082] The SNP used was a non-rod shaped CdSe\CdZnS SNP with CdSe
core diameter of 3.9 nm and overall diameter of 8.9 nm. 0.5 gr of
PVB were dissolved in 4 ml Toluene. 2 mgr of SNP was dissolved in 1
ml Toluene. The SNP solution was added to the polymer mixture while
stirring. After 10 min stirring, the mixture had a shining glow.
The mixture was then transferred to a pattern vessel which was
inserted in a dessiccator and vacuumed for 15 hours, after which
the mixture became solid. The final film thickness was 190 um. FIG.
16 shows the absorption (dotted line) and the PL spectra of this
film. The CWL is at 626 nm and the FWHM is 33 nm. The absorption
ratio between absorption at 455 to maximum absorption in 600-700 nm
range is 1:6 (0.156 to 0.026). The SNP layer was incorporated in a
lighting device as shown in FIG. 5A. A UV LED at 360 nm was used to
illuminate this RSNP layer, and provided light output in the red,
at 626 nm (not shown).
[0083] In conclusion, various embodiments of the invention provide
devices incorporating novel conversion layers based on SNPs.
Conversion layers disclosed herein are characterized by low
re-absorption in the emission region compared with the absorbance
in the exciting wavelength. SNP/RSNP conversion layers disclosed
herein are suitable for enhancing the properties of LED devices to
provide white emission with a CCT<4000K with a high CRI>80
and even >85, in particular a CCT<3500 and even a CCT-2700K
with CRI>89. Polymer embedded SNP conversion layers of the
invention can be further prepared to provide a white colour for
display applications composed of three or more primary colours with
a narrow FWHM<60 nm and even a FWHM<40 nm.
[0084] The invention has been described with reference to
embodiments thereof that are provided by way of example and are not
intended to limit its scope. The described embodiments comprise
different features, not all of which are required in all
embodiments of the invention. Some embodiments of the invention
utilize only some of the features or possible combinations of the
features. Variations of embodiments of the described invention and
embodiments of the invention comprising different combinations of
features than those noted in the described embodiments will occur
to persons of ordinary skill in the art. The scope of the invention
is limited only by the following claims.
[0085] All patents, patent applications and publications mentioned
in this specification are herein incorporated in their entirety by
reference into the specification, to the same extent as if each
individual patent, patent application or publication was
specifically and individually indicated to be incorporated herein
by reference. In addition, citation or identification of any
reference in this application shall not be construed as an
admission that such reference is available as prior art to the
present invention.
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