U.S. patent application number 13/050746 was filed with the patent office on 2011-09-22 for garnet-based phosphor ceramic sheets for light emitting device.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Hironaka Fujii, Pan Guang, Hiroaki Miyagawa, Amane Mochizuki, Rajesh Mukherjee, Toshitaka Nakamura, Bin Zhang.
Application Number | 20110227477 13/050746 |
Document ID | / |
Family ID | 44201981 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110227477 |
Kind Code |
A1 |
Zhang; Bin ; et al. |
September 22, 2011 |
GARNET-BASED PHOSPHOR CERAMIC SHEETS FOR LIGHT EMITTING DEVICE
Abstract
Some embodiments disclosed herein include a lighting apparatus
having a composite. The composite may include a first emissive
layer and a second emissive layer. The first emissive layer may
include a first garnet phosphor having a common dopant. The second
emissive layer may include a second garnet phosphor having the
common dopant. In some embodiments, the first emissive layer and
the second emissive layer are fixed together. Some embodiments
disclosed herein include efficient and economic methods of making
the composite. The method may include, in some embodiments,
sintering an assembly that includes pre-cursor materials for the
first emissive layer and the second emissive layer.
Inventors: |
Zhang; Bin; (San Diego,
CA) ; Mukherjee; Rajesh; (Irvine, CA) ; Fujii;
Hironaka; (Carlsbad, CA) ; Miyagawa; Hiroaki;
(Oceanside, CA) ; Guang; Pan; (Carlsbad, CA)
; Nakamura; Toshitaka; (Osaka, JP) ; Mochizuki;
Amane; (San Diego, CA) |
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
44201981 |
Appl. No.: |
13/050746 |
Filed: |
March 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61315763 |
Mar 19, 2010 |
|
|
|
Current U.S.
Class: |
313/503 ;
252/301.4R |
Current CPC
Class: |
C04B 35/6342 20130101;
C04B 2235/663 20130101; C04B 35/22 20130101; C04B 35/63416
20130101; C04B 35/44 20130101; C04B 2235/3225 20130101; C04B
2235/3418 20130101; C04B 2235/6562 20130101; C04B 2235/6567
20130101; C04B 2235/604 20130101; C04B 35/638 20130101; C04B
2235/6565 20130101; C04B 35/6344 20130101; C04B 2237/343 20130101;
C04B 2237/341 20130101; C04B 2235/3229 20130101; C04B 2235/661
20130101; H01L 33/507 20130101; C04B 35/62665 20130101; C04B
2235/3208 20130101; C04B 2235/3224 20130101; C04B 2235/9661
20130101; C04B 2235/3227 20130101; C04B 2235/3206 20130101; C04B
35/63488 20130101; H01L 33/504 20130101; C09K 11/7774 20130101;
C04B 2235/6581 20130101; B32B 18/00 20130101; C04B 2235/6587
20130101 |
Class at
Publication: |
313/503 ;
252/301.4R |
International
Class: |
H01J 1/63 20060101
H01J001/63; C09K 11/78 20060101 C09K011/78 |
Claims
1. A lighting apparatus comprising: a light source configured to
emit radiation having a wavelength of peak emission between about
360 nm and about 500 nm; and a composite configured to receive at
least a portion of the radiation emitted by the light source,
wherein the composite comprises a first emissive layer and a second
emissive layer; wherein the first emissive layer comprises a first
garnet phosphor and the second emissive layer comprises a second
garnet phosphor, and the first garnet phosphor and the second
garnet phosphor are doped with a common dopant.
2. The lighting apparatus of claim 1, wherein the second emissive
layer is disposed between the first emissive layer and the light
source.
3. The lighting apparatus of claim 1, wherein the composite is
substantially free of resin between the first emissive layer and
the second emissive layer.
4. The lighting apparatus of claim 1, wherein the composite is
substantially free of an adhesive between the first emissive layer
and the second emissive layer.
5. The lighting apparatus of claim 1, wherein each of the first
emissive layer and the second emissive layer has an at least 25%
transmittance.
6. The lighting apparatus of claim 1, wherein the first garnet
phosphor has a first wavelength of peak emission between about 495
nm and about 560 nm.
7. The lighting apparatus of claim 1, wherein the second garnet
phosphor has a second wavelength of peak emission between about 570
nm and about 650 nm.
8. The lighting apparatus of claim 1, wherein the first garnet
phosphor is doped with the common dopant at a concentration in the
range of about 0.05% to about 10.00% by mol.
9. The lighting apparatus of claim 1, wherein the second garnet
phosphor is doped with the common dopant at a concentration in the
range of about 0.05% to about 10.00% by mol.
10. The lighting apparatus of claim 1, wherein the common dopant is
selected from the group consisting of Nd, Er, Eu, Cr, Yb, Sm, Tb,
Ce and Pr.
11. The lighting emitting apparatus of claim 1, wherein the first
garnet phosphor is selected from the group consisting of
Lu.sub.3Al.sub.5O.sub.12:Ce, Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce,
Y.sub.3Al.sub.5O.sub.12:Ce, (Y,Tb).sub.3Al.sub.5O.sub.12:Ce and (Y,
Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce.
12. The lighting emitting apparatus of claim 11, wherein the second
garnet phosphor is Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce.
13. The lighting emitting apparatus of claim 11, wherein the first
garnet phosphor is Lu.sub.3Al.sub.5O.sub.12:Ce, and the second
garnet phosphor is Y.sub.3Al.sub.5O.sub.12:Ce.
14. The lighting apparatus of claim 1, wherein the first emissive
layer and the second emissive layer are ceramic plates or laminated
ceramic tapes.
15. The lighting apparatus of claim 1, wherein the composite
further comprises a third emissive layer, wherein the third
emissive layer comprises a third garnet phosphor having a third
wavelength of peak emission.
16. The lighting apparatus of claim 15, wherein the third
wavelength of peak emission is between about 495 nm and about 540
nm, the first wavelength of peak emission is between about 540 and
about 590 nm, and the second wavelength of peak emission is between
570 nm and about 650 nm.
17. The lighting apparatus of claim 15, wherein the first emissive
layer is disposed between the third emissive layer and the second
emissive layer.
18. The lighting apparatus of claim 15, wherein the first garnet
phosphor is selected from the group consisting of
Lu.sub.3Al.sub.5O.sub.12:Ce and
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce, and the third garnet phosphor
is selected from the group consisting of
Y.sub.3Al.sub.5O.sub.12:Ce, (Y,Tb).sub.3Al.sub.5O.sub.12:Ce. and
(Y, Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce.
19. The lighting emitting apparatus of claim 15, wherein the second
garnet phosphor is Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce.
20. The lighting apparatus of claim 1, wherein the composite
further comprises a first non-emissive layer disposed between the
first emissive layer and the second emissive layer, wherein the
first non-emissive layer is substantially transparent.
21. A method of making a composite comprising: providing an
assembly comprising a first layer and a second layer, wherein the
first layer comprises a first doped garnet phosphor, and the second
layer comprises a second doped garnet phosphor, wherein the first
doped garnet phosphor and the second doped garnet phosphor have a
common dopant; and sintering the assembly to produce the composite.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of priority to
U.S. Application No. 61/315,763, filed Mar. 19, 2010. The priority
document is hereby incorporated by reference in its entirety.
BACKGROUND
[0002] 1. Field
[0003] The present application relates to a lighting apparatus
including a translucent composite of garnet-based emissive
layers.
[0004] 2. Description
[0005] Solid state light emitting devices such as light emitting
diode (LED), organic light emitting diode (OLED) or sometimes
called organic electroluminescent device (OEL), and inorganic
electroluminescent device (IEL) have been widely utilized for
various applications such as flat panel display, indicator for
various instrument, signboard, and ornamental illumination, etc. As
the emission efficiency of these light emitting devices continues
to improve, applications that require much higher luminance
intensity, such as automobile headlights and general lighting, may
soon become feasible. For these applications, white-LED is one of
the promising candidates and have attracted much attention.
[0006] Conventional white-LED have been manufactured based on the
combination of blue-LED and yellow light-emitting YAG phosphor
powder dispersed in plastic encapsulant resin like epoxy and
silicone. However, since the particle size of YAG phosphor powder
utilized for this system is around 1-10 .mu.m, the YAG powders
dispersed in the encapsulant resin medium can cause strong light
scattering. As a result, a considerable portion of both the
incident light from the blue LED and the yellow emitting light from
YAG powders ends up being back scattered and dissipated as a loss
of white light emission.
[0007] One approach to solve this problem is to use one or more
phosphor ceramic plates or laminated films that are positioned to
receive emissions from blue emitting light emitting diodes instead
of phosphor powders suspended in a transparent matrix. With
optimized sintering conditions, combined with the use of phosphors
in nanoparticle form, it is possible to obtain a translucent or
transparent ceramic. Since an LED with translucent/transparent
phosphor ceramics has less backscattering loss while maintaining,
or in some cases, increasing the luminance efficiency of the
phosphor layer, it may emit stronger white light than conventional
YAG powder/resin system. In addition, since a ceramic plate/film is
more stable against heat and light irradiation even under UV,
temperature fluctuation of operational property, durability, and
lifetime of the LED can be improved.
[0008] In order to achieve a lower correlated color temperature
(CCT) and higher color rendering index (CRI) in a YAG:Ce LED
system, a red emitting component is needed. U.S. Patent Publication
No. 2007/0215890, which is hereby incorporated by reference in its
entirety, discloses the use of a red phosphor platelet and a green
phosphor platelet in combination with a blue LED to create a white
light LED. U.S. Pat. No. 7,446,343, which is hereby incorporated by
reference in its entirety, uses yellow and red phosphor layers in
LEDs, where the red phosphor candidates need to have Eu.sup.3+ as
dopant. Due to the use of different dopants for the yellow and the
red layers, they have to be prepared separately. Furthermore, since
Eu.sup.3+-doped compounds have a primary absorption region in the
UV spectra instead of the blue visible light, some have resorted to
using nitride or sulfide phosphors that can be activated by blue
light. For example, U.S. Pat. No. 7,361,938, which is hereby
incorporated by reference in its entirety, discloses the use of a
yellow emitting garnet (YAG:Ce) phosphor and a red emitting nitride
or sulphide phosphor. However, these nitride or sulfide emissive
elements are not desirable due to the processing difficulties
and/or chemical/thermal stability concerns. Thus there is a need
for a white light LED device that utilizes blue light and
green/yellow/red phosphor layers and offers simplified
processing.
[0009] Furthermore, some lighting systems, particularly those for
daily and landscape uses, as well as high power lighting systems
for industrial uses, have a somewhat lower color temperature,
T.ltoreq.3500K, falling into the category of warm white lighting.
If the color temperature is higher, T>4600K, the lighting system
will be categorized as cold white light. For solid-state lighting
purposes, warm white light is especially preferred because it has
the same color temperature as standard incandescent bulbs. Thus,
there is also a need for warm white light LED devices that utilize
blue light and green/yellow/red phosphor layers, as well as simple
and economical processes for making these LED devices.
SUMMARY
[0010] Some embodiments disclosed herein provide a lighting
apparatus comprising a light source configured to emit radiation
having a wavelength of peak emission between about 360 nm and about
500 nm; and a composite configured to receive at least a portion of
the radiation emitted by the light source, wherein the composite
comprises a first emissive layer and a second emissive layer;
wherein the first emissive layer comprises a first garnet phosphor
and the second emissive layer comprises a second garnet phosphor,
and the first garnet phosphor and the second garnet phosphor are
doped with a common dopant.
[0011] In some embodiments, the second emissive layer is disposed
between the first emissive layer and the light source. In some
embodiments, the composite is substantially free of resin between
the first emissive layer and the second emissive layer.
[0012] In some embodiments, the first emissive layer and the second
emissive layer are sintered together. In some embodiments, the
composite is substantially free of an adhesive between the first
emissive layer and the second emissive layer. In some embodiments,
each of the first emissive layer and the second emissive layer has
an at least 25% transmittance.
[0013] In some embodiments, the first garnet phosphor has a first
wavelength of peak emission between about 495 nm and about 560 nm.
In some embodiments, the second garnet phosphor has a second
wavelength of peak emission between about 570 nm and about 650
nm.
[0014] In some embodiments, the first garnet phosphor is doped with
the common dopant at a concentration in the range of about 0.05% to
about 10.00% by mol.
[0015] In some embodiments, the second garnet phosphor is doped
with the common dopant at a concentration in the range of about
0.05% to about 10.00% by mol.
[0016] In some embodiments, the common dopant is selected from the
group consisting of Nd, Er, Eu, Cr, Yb, Sm, Tb, Ce and Pr.
[0017] In some embodiments, the first garnet phosphor is selected
from the group consisting of Lu.sub.3Al.sub.5O.sub.12:Ce,
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce, Y.sub.3Al.sub.5O.sub.12:Ce,
(Y,Tb).sub.3Al.sub.5O.sub.12:Ce and (Y, Gd).sub.3(Al,
Ga).sub.5O.sub.12:Ce. In some embodiments, the second garnet
phosphor is Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce. In some
embodiments, the first garnet phosphor is
Lu.sub.3Al.sub.5O.sub.12:Ce, and the second garnet phosphor is
Y.sub.3Al.sub.5O.sub.12:Ce.
[0018] In some embodiments, the first emissive layer and the second
emissive layer are ceramic plates or laminated ceramic tapes.
[0019] In some embodiments, the composite further comprises a third
emissive layer, wherein the third emissive layer comprises a third
garnet phosphor having a third wavelength of peak emission. In some
embodiments, the third wavelength of peak emission is between about
495 nm and about 540 nm, the first wavelength of peak emission is
between about 540 and about 590 nm, and the second wavelength of
peak emission is between 570 nm and about 650 nm. In some
embodiments, the first emissive layer is disposed between the third
emissive layer and the second emissive layer.
[0020] In some embodiments, the first garnet phosphor is selected
from the group consisting of Lu.sub.3Al.sub.5O.sub.12:Ce and
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce, and the third garnet phosphor
is selected from the group consisting of
Y.sub.3Al.sub.5O.sub.12:Ce, (Y,Tb).sub.3Al.sub.5O.sub.12:Ce. and
(Y, Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce.
[0021] In some embodiments, the second garnet phosphor is
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce.
[0022] In some embodiments, the first emissive layer, the second
emissive layer and the third emissive layer are ceramic plates or
laminated ceramic tapes.
[0023] In some embodiments, the composite further comprises a first
non-emissive layer disposed between the first emissive layer and
the second emissive layer, wherein the first non-emissive layer is
substantially transparent. In some embodiments, the first
non-emissive layer is a ceramic. In some embodiments, the
non-emissive layer consists essentially of a garnet material. In
some embodiments, the non-emissive layer is substantially free of
dopant. In some embodiments, the first non-emissive layer is
substantially impermeable to diffusion of the common dopant.
[0024] In some embodiments, the composite further comprises a
second non-emissive layer disposed between the first emissive layer
and the third emissive layer, wherein the second non-emissive layer
is substantially transparent.
[0025] In some embodiments, each of the first emissive layer, the
second emissive layer and the third emissive layer has an at least
25% transmittance.
[0026] In some embodiments, the wavelength of peak emission of the
light source is between about 450 nm to about 500 nm.
[0027] Some embodiments provide a method of making a composite
comprising providing an assembly comprising a first layer and a
second layer, wherein the first layer comprises a first doped
garnet phosphor, and the second layer comprises a second doped
garnet phosphor, wherein the first doped garnet phosphor and the
second doped garnet phosphor have a common dopant; and sintering
the assembly to produce the composite.
[0028] In some embodiments, the method does not include applying an
adhesive or a resin between the first layer and the second layer
after sintering the assembly.
[0029] In some embodiments, providing the assembly comprises:
providing a first mixture comprising a first garnet phosphor in a
solvent and a second mixture comprising a second garnet phosphor in
the solvent; forming at least one first tape comprising the first
garnet phosphor by casting the first mixture on a first substrate
and allowing the solvent to evaporate; forming at least one second
tape comprising the second garnet phosphor by casting the second
mixture on a second substrate and allowing the solvent to
evaporate; stacking the at least one first tape and the at least
one second tape together to form a tape stack; and compressing and
heating the tape stack to form the assembly.
[0030] In some embodiments, the method further comprises forming at
least one non-emissive tape, and disposing the at least one
non-emissive tape between the at least one first tape and the at
least one second tape.
[0031] In some embodiments, the at least one non-emissive tape
consists essentially of a garnet material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIGS. 1A-C depict exemplary lighting apparatuses having a
composite with two or more emissive layers.
[0033] FIG. 2 shows a preparation flow diagram for one embodiment
of forming the composite by molding and sintering.
[0034] FIG. 3 shows a preparation flow diagram for one embodiment
of forming the composite by laminating and sintering.
[0035] FIG. 4 shows the chromaticity of an exemplary YAG:Ce/Lu1:Ce
laminated composite excited by a blue emitting LED.
[0036] FIG. 5 shows the emission spectrum of an exemplary
YAG:Ce/Lu1:Ce laminated composite excited by a blue emitting
LED.
DETAILED DESCRIPTION
[0037] Disclosed herein are lighting apparatuses having a composite
comprising two or more emissive layers, each emissive layer having
a garnet phosphor doped with a common dopant. Applicants have
discovered that using a common dopant within the composite provides
superior absorption efficiency. In particular, the absorption
efficiency is improved at the excitation wavelength ranging from
360 nm to about 500 nm (preferably about 460 nm). Additionally, by
using garnet materials for each emissive layer, the composite
exhibits superior transparency, and reduced cracking or warping
during heating or cooling.
[0038] Also disclosed are efficient and economic processes for
making the garnet phosphors. Conventional methods for making a
composite with multiple emissive layers require sintering each
layer under separate conditions and subsequently stacking the
emissive layers to form a composite. Some embodiments disclosed
herein provide for sintering the composite in a single step to
reduce the cost and time necessary to prepare the composite. The
composite can be sintered in a single step, in part, because the
similar garnet materials allow sintering under the same conditions.
Furthermore, the common dopant among each layer reduces dopant
diffusion problem during the sintering step, and eliminates the
need to sinter each layer separately. These and other advantages
may be obtained through the teachings of the present
application.
Lighting Apparatus
[0039] Some embodiments provide a lighting apparatus having a light
source and a composite configured to receive at least a portion of
the radiation emitted by the light source. The composite comprises
a first emissive layer and a second emissive layer. The first
emissive layer comprises a first garnet phosphor, and the second
emissive layer comprises a second garnet phosphor, and the first
garnet phosphor and the second garnet phosphor are doped with a
common dopant.
[0040] The light source may, in some embodiments, be configured to
emit radiation having a wavelength of peak emission between about
360 nm and about 500 nm. In some embodiments, the light source
emits radiation having a wavelength of peak emission between about
450 nm and about 500 nm. Some embodiments include a light source
that is a semiconductor LED. As an example, the light source may be
an AlInGaN based single crystal semiconductor material coupled to
an electric source.
[0041] The first emissive layer comprises a first garnet phosphor
doped with a dopant that is the same as the dopant in the second
emissive layer. Thus the first and the second phosphors are doped
with a common dopant. The garnet phosphor may have a composition
D.sub.3E.sub.5O.sub.12. In some embodiments, D and E are
independently selected from trivalent metals. In other embodiments,
D can be selected from Lu, Y, Gd, La, and Tb; and E can be selected
from Al, Ga, and In. In preferred embodiments, D is selected from
Lu and Y, and E is Al. The common dopant may be selected from Nd,
Er, Eu, Cr, Yb, Sm, Tb, Ce and Pr. In some embodiments, the common
dopant is Ce.
[0042] The first garnet phosphor may include a concentration of
common dopant that is effective for the first garnet phosphor to
exhibit fluorescence when exposed to radiation having a wavelength
of peak emission in the range of about 360 nm to about 500 nm. In
some embodiments, the common dopant has a concentration in the
first garnet phosphor ranging from about 0.05 mol % to about 2 mol
%. In some embodiments, the dopant concentration in the first
garnet phosphor may be from about 0.01 mol % to about 5 mol %,
about 0.05 mol % to about 3 mol %, about 0.1 mol % to about 1 mol
%. Non-limiting examples of garnets include
Y.sub.3Al.sub.5O.sub.12:Ce, (Y, Tb).sub.3Al.sub.5O.sub.12:Ce, (Y,
Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce, Lu.sub.3Al.sub.5O.sub.12:Ce,
and Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce. In some embodiments, the
first garnet phosphor is selected from Lu.sub.3Al.sub.5O.sub.12:Ce
and Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce. In some embodiments, the
first garnet phosphor is Lu.sub.3Al.sub.5O.sub.12:Ce, and the
second garnet phosphor is Y.sub.3Al.sub.5O.sub.12:Ce.
[0043] The first garnet phosphor can be selected to adjust the
emitted light from the lighting apparatus. For example, the first
garnet phosphor can be selected to emit yellow or green light when
exposed to the light source. A green emission can be obtained by
selecting Lu.sub.3Al.sub.5O.sub.12:Ce and/or
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce, while a yellow emission can be
obtained by selecting Y.sub.3Al.sub.5O.sub.12:Ce and/or (Y,
Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce. In some embodiments, the first
garnet phosphor has a first wavelength of peak emission between
about 495 nm to about 590 nm. For example, the first wavelength of
peak emission may be between about 495 nm to about 540 nm, or
alternatively the first wavelength of peak emission may be between
about 540 nm to about 590 nm
[0044] The second emissive layer may include a second garnet
phosphor. The second garnet phosphor may be a garnet doped with a
common dopant (i.e., the same dopant that is also present in the
first garnet phosphor). The garnet may be, for example, any of
those materials described above with respect to the first garnet
phosphor. Thus, for example, the garnet may have a composition
D.sub.3E.sub.5O.sub.12, where D and E are trivalent metals. The
second garnet phosphor may include a concentration of common dopant
that is effective for the second garnet phosphor to exhibit
fluorescence when exposed to radiation having a wavelength of peak
emission in the range of about 360 nm to about 500 nm. The second
garnet phosphor may also include a common dopant having a
concentration ranging from about 0.05 mol % to about 10.0 mol %. In
some embodiments, the dopant concentration in the second garnet
phosphor may be from about 0.1 mol % to about 7.5 mol %, about 0.25
mol % to about 5 mol %, about 0.5 mol % to about 3 mol % or about
0.75 mol % to about 2 mol %. In a preferred embodiment, the second
phosphor is Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce.
[0045] The second garnet phosphor may also be selected to adjust
the emitted light from the lighting apparatus. In some embodiments,
the second garnet phosphor has a second wavelength of peak emission
between about 570 nm and about 650 nm. In some embodiments, the
first wavelength of peak emission and the second wavelength of peak
emission are substantially different (e.g., the wavelengths are at
least about 10 nm apart).
[0046] The first garnet phosphor and the second garnet phosphor can
be different garnets. For example, the first garnet phosphor is
Y.sub.3Al.sub.5O.sub.12:Ce and the second garnet phosphor is
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce. In some embodiments, the
emission profile of the second garnet phosphor is substantially
different from the emission profile of the first garnet phosphor
when both phosphors are exposed to radiation having a wavelength of
peak emission in the range of about 360 nm to about 500 nm. In some
embodiments, the first phosphor exhibits a wavelength of peak
emission that is at least about 10 nm apart from any wavelength of
peak emission exhibited by the second phosphor. In some
embodiments, the second garnet phosphor is free of at least one
garnet that is present in the first garnet phosphor. As an example,
the first garnet phosphor includes Y.sub.3Al.sub.5O.sub.12:Ce and
the second garnet phosphor has no more than trace amounts of
Y.sub.3Al.sub.5O.sub.12:Ce. In some embodiments, the concentration
of common dopant is substantially different for the first garnet
phosphor and the second garnet phosphor. For example, the
difference in dopant concentration between the first garnet
phosphor and the second garnet phosphor is at least 0.1 mol %, or
preferably at least 0.5 mol %.
[0047] Some embodiments have a composite with a third emissive
layer comprising a third garnet phosphor. The garnet phosphor may
be a garnet doped with a common dopant (i.e., a dopant also present
in the first garnet phosphor and the second garnet phosphor). The
garnet may be any of those materials described above with respect
to the first garnet phosphor and/or the second garnet phosphor. In
a preferred embodiment, the third garnet phosphor is selected from
Lu.sub.3Al.sub.5O.sub.12:Ce, and
Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce.
[0048] The third garnet phosphor may be selected to adjust the
emitted light from the lighting apparatus. In some embodiments, the
third garnet phosphor has a third wavelength of peak emission
between about 495 nm and about 540 nm. In some embodiments, the
first wavelength of peak emission, the second wavelength of peak
emission and the third wavelength of peak emission are
substantially different (e.g., the wavelengths of peak emission are
each at least about 10 nm apart).
[0049] Similar to above, the third garnet phosphor may be a
different garnet from the first garnet phosphor and the second
garnet phosphor. For example, the first garnet phosphor may be
Y.sub.3Al.sub.5O.sub.12:Ce, the second garnet phosphor may be
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce and the third garnet phosphor
may be Lu.sub.3Al.sub.5O.sub.12:Ce. In some embodiments, the third
garnet phosphor is free of at least one garnet which is present in
the first garnet phosphor and at least one garnet which is present
in the second garnet phosphor. As an example, the first garnet
phosphor may include Y.sub.3Al.sub.5O.sub.12:Ce, the second garnet
phosphor may include Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce, and the
third garnet phosphor may have no more than trace amounts of
Y.sub.3Al.sub.5O.sub.12:Ce and
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce. In some embodiments, the
concentration of common dopant is substantially different for each
of the first garnet phosphor, the second garnet phosphor and the
third garnet phosphor.
[0050] The composite may optionally include one or more
non-emissive layers. The diffusion or migration of dopants between
layers may reduce performance of the lighting apparatus (e.g., by
altering the emission spectrum), and thus a non-emissive layer may
be disposed between emissive layers to reduce diffusion of dopants
between the emissive layers. Thus, in some embodiments, the
non-emissive layer is substantially impermeable to diffusion of the
common dopant. In some embodiments, the non-emissive layer is a
ceramic. As an example, the non-emissive layer may be a material
selected from Y.sub.3Al.sub.5O.sub.12, Lu.sub.3Al.sub.5O.sub.12 and
Al.sub.2O.sub.3. In some embodiments, the non-emissive layer is a
garnet. For example, the non-emissive layer may be
Y.sub.3Al.sub.5O.sub.12 or Lu.sub.3Al.sub.5O.sub.12.
[0051] The non-emissive layer exhibits insignificant emission (if
any) in the visible spectrum when exposed to radiation ranging from
about 360 nm to about 500 nm relative to an emissive layer. In some
embodiments, the non-emissive layer consists essentially of a
material selected from a garnet, Al.sub.2O.sub.3 and combinations
thereof. That is, the non-emissive layer may include a garnet,
Al.sub.2O.sub.3 and other materials that do not substantially alter
the non-emissive property. For example, the non-emissive layer may
comprise a garnet material, but not the amount of dopant effective
to result in emission. In some embodiments, the non-emissive layer
consists essentially of a garnet. In some embodiments, the
non-emissive layer is free of dopant (e.g., no more than trace
amounts of dopant).
[0052] In some embodiments, the total light transmittance of each
of the emissive layers at the peak wavelength of emission, or the
peak wavelength of the photoluminescent spectrum of the phosphor
material, is at least about 25% of the theoretical total light
transmittance, preferably at least about 40% of the theoretical
total light transmittance, preferably at least about 60% of the
theoretical total light transmittance. In some embodiments, the
total light transmittance of each of the non-emissive layers is
also at least about 60% of the theoretical total light
transmittance, preferably at least about 70% of the theoretical
total light transmittance, more preferably at least about 80% of
the theoretical total light transmittance.
[0053] The layers of the composite, such as the emissive and
non-emissive layers, may be coupled together. In some embodiments,
the layers are coupled together by sintering. In some embodiments,
the layers are coupled together by sintering the layers while
adjacent layers are in contact. As an example, precursor materials
(e.g., a mold or laminated tapes) for each layer are stacked to
form an assembly. The assembly can then be sintered such that
adjacent layers are fixed together. In some embodiments, the
composite may be coupled together without using a resin and/or
adhesive. In some embodiments, the composite is substantially free
of resin and adhesive between adjacent layers. A composite is
"substantially free of resin" when free of an effective amount of
resin to fix the two layers together. For example, a composite
having a first emissive layer and second emissive layer can be
substantially free of resin between the first emissive layer and
the second emissive layer. Accordingly, the amount of resin (if
any) between the first emissive layer and the second emissive layer
is insufficient to fix the layers together. In some embodiments,
the composite is substantially free of adhesive between adjacent
layers.
[0054] FIG. 1A is an exemplary lighting apparatus having a
composite with two emissive layers. A submount 100 has a light
source 105 (e.g., a LED) mounted thereon. First emissive layer 110
is disposed above the second emissive layer 115 and receives at
least a portion of the radiation emitted from the light source 105.
Second emissive layer 115 is disposed between the conventional base
LED 105 and the first emissive layer 110. The second emissive layer
115 receives at least a portion of the radiation emitted from the
light source 105. An optional encapsulant resin 120 is placed over
the light source 105, the first emissive layer 110 and the second
emissive layer 115. In some embodiments, the first emissive layer
110 and the second emissive layer 115 are fixed together to form a
composite.
[0055] FIG. 1B is another exemplary lighting apparatus having a
composite with two emissive layers and one non-emissive layer.
Non-emissive layer 125 is interposed between the first emissive
layer 110 and the second emissive layer 115. In an embodiment, the
first emissive layer 110, the second emissive layer 115, and the
non-emissive layer 125 are fixed together to form a composite.
[0056] FIG. 1C is an exemplary lighting apparatus having a
composite with three emissive layers. First emissive layer 110 is
interposed between the second emissive layer 115 and the third
emissive layer 130. The third emissive layer 130 is configured to
receive at least a portion of the radiation emitted from the light
source 105. In some embodiments, the first emissive layer 110, the
second emissive layer 115, and the third emissive layer 130 are
fixed together to form a composite.
[0057] The location of the various components (e.g., the lights
source 105, first emissive layer 110, etc.) in the lighting
apparatus is not particularly limited. In some embodiments, the
components are configured so that both the first emissive layer and
the second emissive layer receive at a least a portion of the
radiation emitted from the light source. Light emitted from the
second emissive layer may be reabsorbed by the first emissive
layer, which can diminish the efficiency and/or CRI of the lighting
apparatus. Thus, the first emissive layer and the second emissive
layer may be configured to reduce emitted light from the second
emissive layer that is received by the first emissive layer. In
some embodiments, the second emissive layer is disposed at least
partially between the light source and the first emissive layer. In
some embodiments, the emission layers are configured so that there
is little overlap between the emission spectrum of the second
emissive layer and the excitation spectrum of the first emissive
layer. By minimizing the overlap, only a small amount of light
emitted from the second layer can be absorbed by the first emissive
layer. As a result, the efficiency and/or CRI of the lighting
apparatus is not compromised or reduced.
[0058] The phosphor compositions may be encapsulated in a mold
(e.g., as illustrated by encapsulated phosphor powder 120). For
example, the composition may be formed into a mold by encapsulating
the first phosphor and the second phosphor in a resin, such as an
epoxy or silicone. Examples and methods for encapsulating the
phosphors are disclosed in U.S. Pat. Nos. 5,998,925 and 6,069,440,
both of which are hereby incorporated by reference in their
entirety.
[0059] By selecting appropriate emissive layers, the lighting
apparatus can exhibit a CRI of at least 70 when exposed to light.
In other embodiments, the CRI is at least 72; at least 75; or at
least 80. The CRI refers to the ability to render various colors
and has values ranging from 0 to 100, with 100 being the best. The
reference correlated color temperature (CCT) for the CRI may be in
the range about 2000 K to about 4000K; in the range of about 2500 K
to about 3500 K; or about 2600K to about 3400 K.
Molding and Sintering to Form Composites
[0060] The lighting apparatus can include a first emissive layer
having a first garnet phosphor and a second emissive layer having a
second garnet phosphor (e.g., as illustrated in FIGS. 1A-C). The
emissive layers may, in some embodiments, be ceramic plates. In
some embodiment, the non-emissive layer can be a ceramic plate. The
ceramic plates may be fixed together to form a composite.
[0061] In some embodiments, each ceramic plate independently
includes a multiphasic material having about 85% to about 99.99% by
volume of an emissive phase (e.g., the first garnet phosphor or the
second garnet phosphor) and about 15% to about 0.01% by volume of a
non-emissive phase. In some embodiments, the lighting apparatus may
include a first ceramic plate having at least 85% by volume of the
first phosphor, and a second ceramic plate having at least 85% by
volume of the second phosphor. The ceramic plates are configured to
receive at least a portion of light emitted from a light
source.
[0062] The ceramic plates may be prepared by molding and sintering
phosphor mixtures. Exemplary ceramic plates and methods of making
the same are disclosed U.S. Publication No. 2009/0212697, which is
hereby incorporated by reference in its entirety. FIG. 2 shows a
preparation flow diagram for one embodiment of forming the
composite by molding and sintering.
[0063] First, raw garnet phosphor powders are provided, such as the
first garnet phosphor and the second garnet phosphor described
herein. The raw powders may be prepared using any conventional or
suitable methods, such as the flow-based thermochemical synthetic
routes described herein. In some embodiments, raw powders of
phosphor materials used to make the composite are typically
nano-sized particles with average particle size no greater than
about 1000 nm, preferably no greater than about 500 nm, more
preferably no greater than 200 nm. If the particle size is greater
than about 1000 nm, it can be very difficult to make total light
transmittance higher than about 50%, because such large particles
do not easily fuse with each other even at a high temperature and
high pressure sintering condition. The result would be a tendency
for a lot of air voids to remain in the ceramic plate. On the other
hand, nano-sized particles can easily fuse with each other, which
enable us to prepare fine and air void free ceramic plates.
[0064] The raw materials are not required to have the same
composition or crystal structure of resultant phosphor ceramic
plate. For example, a YAG:Ce ceramic plate may be made by using
YAG:Ce powders, Y--Al--O--Ce containing amorphous powders, a
mixture of YAlO.sub.3:Ce and Al.sub.2O.sub.3 powders, a mixture of
Y.sub.2O.sub.3, Al.sub.2O.sub.3, and CeO.sub.2 powders, and any
combination thereof.
[0065] In some embodiments, small quantities of flux materials
(e.g., sintering aids) may be used in order to improve sintering
properties if desired. In some embodiments, the sintering aids may
include, but are not limited to, tetraethyl orthosilicate (TEOS),
colloidal silica, lithium oxide, titanium oxide, zirconium oxide,
magnesium oxide, barium oxide, calcium oxide, strontium oxide,
boron oxide, or calcium fluoride. Additional sintering aids
include, but are not limited to, alkali metal halides such as NaCl
or KCl, and organic compounds such as urea. In some embodiments,
the sintered ceramic plate comprises between about 0.01% and about
5%, between about 0.05% and about 5%, between about 0.1% and about
4%, or between about 0.3% and about 1% by weight of the flux
material(s) or sintering aid(s). The sintering aid can be
intermixed with the raw materials. For example, in some
embodiments, tetraethyl orthosilicate (TEOS) can be added to the
raw materials to provide the desired amount of sintering aid. In
one embodiment, about 0.05% to about 5% by weight of TEOS is
provided to the sintered ceramic plate. In some embodiments, the
amount of TEOS may be between about 0.3% and about 1% by
weight.
[0066] Various plasticizers may also be included, in some
embodiments, to reduce the glass transition temperature and/or
improve flexibility of the ceramic. Non-limiting examples of
plasticizers include dicarboxylic/tricarboxylic ester-based
plasticizers, such as bis(2-ethylhexyl) phthalate, diisononyl
phthalate, bis(n-butyl)phthalate, butyl benzyl phthalate,
diisodecyl phthalate, di-n-octyl phthalate, diisooctyl phthalate,
diethyl phthalate, diisobutyl phthalate, and di-n-hexyl phthalate;
adipate-based plasticizers, such as bis(2-ethylhexyl)adipate,
dimethyl adipate, monomethyl adipate, and dioctyl adipate;
sebacate-based plasticizers, such as dibutyl sebacate, and maleate;
dibutyl maleate; diisobutyl maleate; polyalkylene glycols such as
polyethylene glycol, polypropylene glycol, and copolymers thereof;
benzoates; epoxidized vegetable oils; sulfonamides, such as N-ethyl
toluene sulfonamide, N-(2-hydroxypropyl)benzene sulfonamide, and
N-(n-butyl)benzene sulfonamide; organophosphates, such as tricresyl
phosphate, tributyl phosphate; glycols/polyethers, such as
triethylene glycol dihexanoate, tetraethylene glycol diheptanoate;
alkyl citrates, such as triethyl citrate, acetyl triethyl citrate,
tributyl citrate, acetyl tributyl citrate, trioctyl citrate, acetyl
trioctyl citrate, trihexyl citrate, acetyl trihexyl citrate,
butyryl trihexyl citrate, and trimethyl citrate; alkyl sulphonic
acid phenyl ester; and mixtures thereof.
[0067] In some embodiments, the mixing and molding process may be
made easier by occasionally adding binder resin and solvent to the
raw powders. A binder is any substance that improves adhesion of
the particles of the composition being heated to form a composite.
Some non-limiting examples of binders include polyvinyl alcohol,
polyvinyl acetate, polyvinyl chloride, polyvinyl butyral,
polystyrene, polyethylene glycol, polyvinylpyrrolidones, polyvinyl
acetates, and polyvinyl butyrates, etc. In some, but not all,
circumstances, it may be useful for the binder to be sufficiently
volatile that it can be completely removed or eliminated from the
precursor mixture during the sintering phase. Solvents which may be
used in include, but not limited to water, a lower alkanol such as
but not limited to denatured ethanol, methanol, isopropyl alcohol
and mixtures thereof, preferably denatured ethanol, xylenes,
cyclohexanone, acetone, toluene and methyl ethyl ketone, and
mixtures thereof. In a preferred embodiment, the solvent is a
mixture of xylenes and ethanol.
[0068] The mixing process can be done using a mortar and pestle,
ball milling machine, bead milling machine or other equivalent
equipments. For the molding process, a simple die for tablet
molding, hot isostatic pressing (HIP), or cold isostatic pressing
(CIP) may be utilized. In some embodiments, controlled quantities
of raw powders are loaded in a mold followed by applying pressure
to form the plate.
[0069] Two or more molds are then stacked to form an assembly,
which is subsequently sintered to form a composite. The arrangement
of the molds will determine the configuration of the final
composite. Thus, for example, an assembly may include a first mold
having the first garnet phosphor and a second mold having the
second garnet phosphor. This assembly can then be sintered to form
a composite including the first emissive layer having the first
phosphor and the second emissive layer having the second phosphor.
As an example, a composite including the first emissive layer 110
and the second emissive 115, as illustrated in FIG. 1A.
Accordingly, a person of ordinary skill, guided by the teachings of
the present application, can prepare various composite
configurations, such as those disclosed above, by appropriately
stacking the molds prior to sintering.
[0070] As disclosed above, non-emissive layers may also be included
in the composite. A non-emissive layer may be prepared, for
example, by preparing a mold of YAG powder that excludes amounts of
dopant that are effective to produce fluorescence. The mold may be
included in the stacked assembly that is subsequently sintered to
form the composite.
[0071] The assembly is then sintered at a high temperature that
does not exceed the melting point of the resultant phosphor
materials. Thus, by sintering the assembly having two or more
molds, a single sintering process is used to prepare a composite
having two or more emissive layers. The emissive layers in the
composite, in some embodiments, are coupled together upon
completion of the sintering process. In some embodiments, the
composite is fixed together upon completion of the sintering
process.
[0072] Any kinds of suitable ceramic sintering techniques can be
used to prepare translucent ceramic plates. In some embodiments,
sintering may be carried out while applying pressure. Sintering
conditions such as the temperature profile, atmosphere, pressure,
and duration depend on the type of phosphor material.
Laminating and Sintering to Form Composites
[0073] The composite may be formed by laminating and sintering two
or more cast tapes, where the cast tapes can include the first
phosphor and/or the second phosphor. Examples and methods of
laminating and sintering two or more cast tapes are disclosed in
U.S. Pat. No. 7,514,721 and U.S. Publication No. 2009/0108507, both
of which are hereby incorporated by reference in their entirety.
FIG. 3 shows a preparation flow diagram for one embodiment of
forming the ceramic plate by laminating and sintering.
[0074] First, the particle size of the raw materials (e.g., nitrate
or oxide based raw materials, such as Y.sub.2O.sub.3 and
Al.sub.2O.sub.3 for forming YAG) may optionally be adjusted to
reduce cracking in the cast tapes from capillary forces during
evaporation of solvents. For example, the particle size can be
adjusted by pre-annealing raw material particles to obtain the
desired particle size. Raw material particles can be pre-annealed
in the temperature range of about 800.degree. C. to about
1800.degree. C. (or more preferably 1000.degree. C. to about
1500.degree. C.) to obtain the desired particle size. The
pre-annealing may occur in a vacuum, air, O.sub.2, H.sub.2,
H.sub.2/N.sub.2, or a noble gas (e.g., He, Ar, Kr, Xe, Rn, or
combinations thereof). In an embodiment, each of the raw materials
(e.g., Y.sub.2O.sub.3 and Al.sub.2O.sub.3 for forming YAG) is
adjusted to be about the same particle size. In another embodiment,
the particles have a BET surface area in the range of about 0.5
m.sup.2/g to about 20 m.sup.2/g (preferably about 1.0 m.sup.2/g to
about 10 m.sup.2/g, or more preferably about 3.0 m.sup.2/g to about
6.0 m.sup.2/g).
[0075] A slurry may then be prepared for subsequently casting into
a tape. Pre-made phosphors (e.g., phosphors prepared by flow-based
thermochemical synthetic routes described herein) and/or
stoichiometric amounts of raw materials can be intermixed with
various components to form a mixture. Exemplary components for the
mixture include, but are not limited to, dopants, dispersants,
plasticizers, binders, sintering aids and solvents. The dopants,
sintering aids, plasticizers, binders and solvents may be the same
as those described above with respect to the molding and sintering
process.
[0076] In some embodiments, the dispersants can be Flowen, fish
oil, long chain polymers, steric acid, oxidized Menhaden fish oil,
dicarboxylic acids such succinic acid, orbitan monooleate,
ethanedioic acid, propanedioic acid, pentanedioic acid, hexanedioic
acid, heptanedioic acid, octanedioic acid, nonanedioic acid,
decanedioic acid, o-phthalic acid, p-phthalic acid and mixtures
thereof.
[0077] The mixture may then be subjected to comminution to form a
slurry by, for example, ball milling the mixture for a time period
in the range of about 0.5 hrs. to about 100 hrs. (preferably about
6 hrs. to about 48 hrs., or more preferably about 12 hrs. to about
24 hrs.). The ball milling may utilize milling balls that include
materials other than the components intermixed within the mixture
(e.g., the milling balls may be ZnO.sub.2 for a mixture that forms
YAG). In an embodiment, the ball milling includes isolating the
milling balls after a period of time by filtration or other known
methods of isolation. In some embodiments, the slurry has a
viscosity in the range of about 10 cP to about 5000 cP (preferably
about 100 cP to about 3000 cP, or more preferably about 400 cP to
1000 cP).
[0078] Third, the slurry may be cast on a releasing substrate
(e.g., a silicone coated polyethylene teraphthalate substrate) to
form a tape. For example, the slurry may be cast onto a moving
carrier using a doctor blade and dried to form a tape. The
thickness of the cast tape can be adjusted by changing the gap
between the doctor blade and the moving carrier. In some
embodiments, the gap between the doctor blade and the moving
carrier is in the range of about 0.125 mm to about 1.25 mm
(preferably about 0.25 mm to about 1.00 mm, or more preferably
about 0.375 mm to about 0.75 mm). Meanwhile, the speed of the
moving carrier can have a rate in the range of about 10 cm/min. to
about 150 cm/min. (preferably about 30 cm/min. to about 100
cm/min., or more preferably about 40 cm/min. to about 60 cm/min.).
By adjusting the moving carrier speed and the gap between the
doctor blade and moving carrier, the tape can have a thickness
between about 20 .mu.m and about 300 .mu.m. The tapes may
optionally be cut into desired shapes after casting.
[0079] Two or more tapes are laminated to form an assembly. The
lamination step can include stacking two or more tapes (e.g., 2 to
100 tapes are stacked) and subjecting the stacked tapes to heat and
uniaxial pressure (e.g., pressure perpendicular to the tape
surface). For example, the stacked tapes may be heated above the
glass transition temperature (T.sub.g) of the binder contained in
the tape and compressed uniaxially using metal dies. In some
embodiments, the uniaxial pressure is in the range of about 1 to
about 500 MPa (preferably about 30 MPa to about 60 MPa). In some
embodiments, the heat and pressure is applied for a time period in
the range of about 1 min. to about 60 min. (preferably about 15
min. to about 45 min., or more preferably about 30 min.). The
lamination step may optionally include forming various shapes
(e.g., holes or pillars) or patterns into the assembly by, for
example, using shaped dies.
[0080] Some embodiments of the assembly include at least one tape
having the first garnet phosphor and at least one tape having the
second garnet phosphor. The arrangement of the stacked tapes is not
particularly limited, however the tapes may be stacked so all of
the tapes including the first phosphor are stacked together and all
of the tapes including the second phosphor are stacked together.
Similar to the discussion above with regard to the stacking of
molds to form the assembly, the configuration of the stacked tapes
will correspond with the configuration of the composite.
[0081] The assembly may be heated to form the composite. The
heating step may include a debinding process and a sintering
process. The debinding process includes decomposing at least a
portion of organic components within the assembly (e.g., volatilize
binders and plasticizers within the assembly). As an example, the
assembly may be heated in air to a temperature in the range of
about 300.degree. C. to about 1200.degree. C. (preferably about
500.degree. C. to about 1000.degree. C., or more preferably about
800.degree. C.) at a rate of about 0.1.degree. C./min. to about
10.degree. C./min. (preferably about 0.3.degree. C./min. to about
5.degree. C./min., or more preferably about 0.5.degree. C./min. to
about 1.5.degree. C./min). The exemplary heating step may also
include maintaining the temperature for a time period in the range
of about 30 min. to about 300 min, which may be selected based upon
the thickness of the assembly.
[0082] The heating step also includes a sintering process to form
the composite. The assembly may be sintered in a vacuum, air,
O.sub.2, H.sub.z, H.sub.z/N.sub.2, or a noble gas (e.g., He, Ar,
Kr, Xe, Rn, or combinations thereof) at a temperature in the range
of about 1200.degree. C. to about 1900.degree. C. (preferably about
1300.degree. C. to about 1800.degree. C., or more preferably about
1350.degree. C. to about 1700.degree. C.) for a time period in the
range of about 1 hr. to about 100 hrs (preferably about 2 hrs. to
about 10 hrs.). In some embodiments, the debinding and sintering
processes are completed in a single step.
[0083] The assembly may be sandwiched between cover plates during
the heating step to reduce distortion (e.g., warping, cambering,
bending, etc.) of the assembly. The cover plates may include
materials having a melting point above the temperatures applied
during the heating step. Moreover, the cover plate may be
sufficiently porous to permit transport of volatilized components
through the covering plates. As an example, the covering plate may
be zirconium dioxide having a porosity of about 40%.
[0084] An optional reoxidation step may also be included to improve
the transmittance of the composite. Reoxidation can include
exposing the composite to oxygen or air at a temperature in the
range of about 1000.degree. C. to about 1500.degree. C. (preferably
about 1400.degree. C.) for a time period of about 30 min. to about
300 min. (preferably about 2 hrs.) at a heating rate of about
1.degree. C./min. to about 20.degree. C./min. (preferably about
5.degree. C./min.).
[0085] The lighting apparatus may include non-emissive layers
(e.g., non-emissive layer 125 illustrated in FIG. 1B). The
non-emissive layer can be a ceramic plate which may also be
prepared using similar laminating and sintering procedures as those
described above. A non-emissive layer may be prepared, for example,
by laminating and sintering a YAG powder into the assembly that
excludes amounts of dopant that are effective to produce
fluorescence.
EXAMPLES
[0086] Additional embodiments are disclosed in further detail in
the following examples, which are not in any way intended to limit
the scope of the claims.
Example 1
Warm White Light Emitting Composite
[0087] The following example demonstrates forming a composite for
the emission of warm white light.
Example 1.1
YAG:Ce
[0088] 0.14923 mol (14.29 g) of Yttrium (III) nitrate hexahydrate
(99.9% pure, Sigma-Aldrich), 0.25 mol (23.45 g) of Aluminum nitrate
nonahydrate (99.97% pure, Sigma-Aldrich), and 0.015 mol (0.081 g)
of Cerium (III) nitrate hexahydrate (99.99% pure, Sigma-Aldrich)
were dissolved in 250 ml of deionized water, followed by
ultrasonication for 30 min to prepare the transparent precursor
solution. This pre-cursor solution of 0.4 M was carried into a
plasma reaction chamber via an atomization probe using a liquid
pump.
[0089] All deposition experiments were conducted with an RF
induction plasma torch (TEKNA Plasma System, Inc PL-35) operating
at 3.3 MHz. For the deposition experiments, the chamber pressure
was kept at around 25 kPa-35 kPa, and the RF generator plate power
was in the range of 10-12 kW. Both the plate power and the
deposition pressure are user-controlled parameters. Argon was
introduced into the plasma torch as both the swirling sheath gas
and the central plasma gas via the gas inlet ports. Sheath gas flow
was maintained at 30 slm (standard liters per minute), while
central gas flow was 10 slm.
[0090] Reactant injection was performed using a radial atomization
probe (TEKNA Plasma System, Inc SDR-772). The probe was positioned
at the center of the plasma plume during reactant injection. The
reactants were fed into the plasma plume at a rate of 10 ml/min
during deposition. Atomization of the liquid reactant was performed
with Argon as atomizing gas delivered at a flow rate of 15 slm. The
cooling water supply to the atomization probe was maintained at a
flow rate of 4 slm and at a pressure of 1.2 MPa, as recommended by
the manufacturer.
[0091] Crystalline phases of the deposited particles were
investigated using X-ray diffraction (XRD) spectra obtained with a
Bruker AXS micro-diffractometer (CuK.alpha.). The crystalline phase
of the obtained sample was identified as a mixture of amorphous and
yttrium aluminum perovskite (YAP). The average particle diameter
(D.sub.avg) was obtained from BET surface area based on data
acquired from a Micrometritics model Gemini 2365 gas sorptometer.
The obtained D.sub.avg of the sample was 75 nm.
Example 1.2
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce
[0092] The procedure of Example 1.1 was followed except that 52.612
g of Lutetium nitrate hydrate (46.8% pure, Metall Rare Earth
Limited, ShenZhen, P.R.China), 14.899 g of Calcium nitrate
tetrahydrate (99% pure, Sigma-Aldrich), 32.374 g of Magnesium
nitrate hexahydrate (99% pure, Fluka), 102.908 g of
Aminopropylsilanetriol (25% in water, Gelest), and 0.543 g of
Cerium (III) nitrate hexahydrate (99.99% pure, Sigma-Aldrich) were
dissolved in 250 ml of deionized water, followed by ultrasonication
for 30 min to prepare the transparent precursor solution. This
precursor solution of 0.4 M was carried into a plasma reaction
chamber via an atomization probe using a liquid pump.
Example 1.3
Preparation of Non-Emissive (Undoped) Material
[0093] The preparation of the non-emissive material was prepared
similarly to that described above, except that no Cerium (III)
nitrate hexahydrate was added to 0.14923 mol (14.29 g) of Yttrium
(III) nitrate hexahydrate (99.9% pure, Sigma-Aldrich), 0.25 mol
(23.45 g) of Aluminum nitrate nonahydrate (99.97% pure,
Sigma-Aldrich).
Example 1.4
Preparation of Sintered Ceramic Plates of YAG:Ce Phosphor
Material
[0094] Sintered ceramic plates were made using YAG:Ce phosphor
nano-powders. 4 g of nano-powder prepared by the method described
above, 0.21 g of poly(vinyl butyral-co-vinyl alcohol-co-vinyl
acetate) (average Mw 90,000-120,000 powder, Sigma-Aldrich), 0.012 g
of fumed silica powder (CAB-O-SIL.RTM. HS-5, Cabot Corporation),
and 10 ml of ethanol were well mixed by mortar and pestle until the
mixture slurry solution became very smooth. By blowing hot air from
a dryer and keeping the pestle moving, ethanol was completely
removed, and dry powders were obtained. Then 120 mg of the dry
powders were spread out into a 3 mm diameter die (Product#:
0012-6646, 3 mm KBr Die Set, International Crystal Laboratories,
Inc), followed by applying a pressure of 4000 psi using hydraulic
press. Then the obtained plates were sintered at 800.degree. C. for
2 hrs (heating rate of 2.degree. C./min) using a box electrical
furnace under an air ambient, and then at 1500.degree. C. for 5 hrs
(heating rate is 5.degree. C./min) using tube electrical furnace
under vacuum. The crystalline phase of all ceramic plate samples
was determined as yttrium aluminum garnet by XRD.
Example 1.5
Preparation of Sintered Ceramic Plates of
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce Phosphor Material
[0095] The procedure of Example 1.4 was followed except that 4 g of
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce, as prepared in Example 1.2,
and the obtained plates were sintered at 1400.degree. C. for 5 hrs
under vacuum.
Example 2
Laminated Composite of Emissive Layers
[0096] The following example demonstrates the emission of warm
white light by a composite formed by lamination.
Example 2.1
Non-Emissive Layers for Laminated Composite
[0097] A 50 ml high purity Al.sub.2O.sub.3 ball mill jar was filled
with 55 g of Y.sub.2O.sub.3-stabilized ZrO.sub.2 ball of 3 mm
diameter. Then, in a 20 ml glass vial, 0.153 g dispersant (Flowlen
G-700. Kyoeisha), 2 ml xylene (Fisher Scientific, Laboratory grade)
and 2 ml ethanol (Fisher Scientific, reagent alcohol) were mixed
until the dispersant was dissolved completely. The dispersant
solution and tetraethoxysilane as sintering aid (0.038 g, Fluka)
were added to a ball mill jar.
[0098] Y.sub.2O.sub.3 powder (3.984 g, 99.99%, lot N-YT4CP, Nippon
Yttrium Company Ltd.) with a BET surface area of 4.6 m.sup.2/g and
Al.sub.2O.sub.3 powder (2.998 g, 99.99%, grade AKP-30, Sumitomo
Chemicals Company Ltd.) with a BET surface area of 6.6 m.sup.2/g
were added to ball mill jar. The total powder weight was 7.0 g and
the ratio of Y.sub.2O.sub.3 to Al.sub.2O.sub.3 was at a
stoichiometric ratio of 3:5. A first slurry was produced by mixing
the Y.sub.2O.sub.3 powder, the Al.sub.2O.sub.3 powder, dispersant,
tetraethoxysilane, xylenes, and ethanol by ball milling for 24
hours.
[0099] A solution of binder and plasticizers was prepared by
dissolving 3.5 g poly(vinyl butyral-co-vinyl alcohol-co-vinyl
acetate) (Aldrich), 1.8 g benzyl n-butyl phthalate (98%, Alfa
Aesar), and 1.8 g polyethylene glycol (Mn=400, Aldrich) in 12 ml
xylene (Fisher Scientific, Laboratory grade) and 12 ml ethanol
(Fisher Scientific, reagent alcohol). A second slurry was produced
by adding 4 g of the binder solution into the first slurry and then
milling for another 24 hours. When ball milling was complete, the
second slurry was passed through a syringe-aided metal screen
filter with pore size of 0.05 mm. Viscosity of second slurry was
adjusted to 400 centipoise (cP) by evaporating solvents in the
slurry while stirring at room temperature. The slurry was then cast
on a releasing substrate, e.g., silicone coated Mylar.RTM. carrier
substrate (Tape Casting Warehouse) with an adjustable film
applicator (Paul N. Gardner Company, Inc.) at a cast rate of 30
cm/min. The blade gap on the film applicator was set at 0.508 mm
(20 mil). The cast tape was dried overnight at ambient atmosphere
to produce a green sheet of about 140 .mu.m thickness.
Example 2.2
YAG:Ce Layers
[0100] Plasma-produced yttrium aluminum oxide (with stoichiometry
Y:Al:O=3:5:12) powders (5.2 g) containing 0.2 mol % cerium with
respect to yttrium with a BET surface area of about 20 m.sup.2/g
was added to a high purity alumina combustion boat followed by
annealing in a tube furnace (MTI GSL-1600) at heating ramp of
3-5.degree. C./min to 1250.degree. C. in air or 3% H.sub.2/97%
N.sub.2 for 2 hrs. Then, it was cooled down to room temperature at
a ramp of 5.degree. C./min. Yellow color powder with a BET surface
area of 4.6 m.sup.2/g was obtained after annealing.
[0101] A 50 ml high purity Al.sub.2O.sub.3 ball mill jar was filled
with 24 g Y.sub.2O.sub.3 stabilized ZrO.sub.2 ball of 3 mm
diameter. Then, in a 20 ml glass vial, 0.084 g dispersant (Flowlen
G-700. Kyoeisha), 2 ml xylene (Fisher Scientific, Laboratory
grade), and 2 ml ethanol (Fisher Scientific, reagent alcohol) were
mixed until the dispersant was dissolved completely. The dispersant
solution and tetraethoxysilane as a sintering aid (0.045 g 99.0%
pure, Fluka) were added to a ball mill jar. The annealed plasma YAG
powder (3.0 g) with a BET surface area of 4.6 m.sup.2/g, was added
to a ball mill jar. The first slurry was produced by mixing the YAG
powder, dispersant, tetraethoxysilane, xylenes, and ethanol by ball
milling for 24 hours.
[0102] A solution of binder and plasticizers was prepared by
dissolving 5.25 g poly(vinyl butyral-co-vinyl alcohol-co-vinyl
acetate) (Aldrich), 2.6 g benzyl n-butyl phthalate (98%, Alfa
Aesar), and 2.6 g polyethylene glycol (Mn=400, Aldrich) in 18 ml
xylene (Fisher Scientific, Laboratory grade) and 18 ml ethanol
(Fisher Scientific, reagent alcohol). A second slurry was produced
by adding 1.2 g of the binder solution into the first slurry and
then milling another 24 hours. When ball milling was complete, the
second slurry was passed through a syringe-aided metal screen
filter with pore size of 0.05 mm. The viscosity of the second
slurry was adjusted to 400 centipoise (cP) by evaporating solvents
in the slurry while being stirred at room temperature. The slurry
was then cast on a releasing substrate, e.g., silicone coated
Mylar.RTM. carrier substrate (Tape Casting Warehouse) with an
adjustable film applicator (Paul N. Gardner Company, Inc.) at a
cast rate of 30 cm/min. The blade gap on the film applicator was
set at 0.508 mm (20 mil). The cast tape was dried overnight at
ambient atmosphere to produce a yellow-colored green sheet of about
140 .mu.m thickness.
Example 2.3
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce
[0103] The procedure of Example 2.2 was followed except that 3.0 g
of Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce, which contained 1 mol %
cerium with respect to lutetium, as prepared in Example 1.2, were
used instead of YAG:Ce powder.
Example 2.4
Laminating Layers
[0104] The dried cast tape of the first phosphor material (300
.mu.m thickness) comprising the annealed plasma YAG:Ce powders, the
dried cast tape of the non-emissive material (100 .mu.m thickness)
comprising YAG with no Ce powder, as well as the dried cast tape
comprising the annealed plasma
Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce powders (250 .mu.m thickness)
were cut into circular shapes of 13 mm diameter with a metal
puncher. The respective pieces of punched circular-shaped tapes
were placed between circular dies with mirror-polished surfaces and
heated on a hot plate to 80.degree. C., and subsequently compressed
in a hydraulic press at a uniaxial pressure of 5 metric tons for 5
minutes. Laminated composites of emissive (first phosphor material
and second phosphor material) and non-emissive layers were thus
produced.
[0105] For debinding, laminated green sheets were sandwiched
between ZrO.sub.2 cover plates (1 mm in thickness, grade 42510-X,
ESL Electroscience Inc.) and placed on an Al.sub.2O.sub.3 plate of
5 mm thickness. The sandwiched laminate was then heated in a tube
furnace in air at a ramp rate of 0.5.degree. C./min to 800.degree.
C. and held for 2 hours to remove the organic components from the
green sheets to generate a preform.
[0106] After debinding, the preforms were annealed at 1500.degree.
C. in a vacuum of 10.sup.-1 Torr for 5 hours at a heating rate of
1.degree. C./min to complete conversion from non-garnet phases of
Y--Al--O in the non-emissive layer, including, but not limited to,
amorphous yttrium oxides, YAP, YAM or Y.sub.2O.sub.3 and
Al.sub.2O.sub.3 to yttrium aluminum garnet (YAG) phase, and the
conversion from amorphous Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce to
crystallized Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce phase as well as
increase the final YAG and Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce
grain size.
[0107] Following the first annealing, the preforms were further
sintered in a vacuum of 10.sup.-3 Torr at about 1650.degree. C. for
2 hours at a heating rate of 5.degree. C./min and a cooling rate of
10.degree. C./min to room temperature to produce a translucent
YAG/YAG:Ce/Lu.sub.2CaMg.sub.2Si.sub.3O.sub.12:Ce/YAG ceramic sheet
of about 0.60 mm thickness. When the laminated green sheets were
annealed in the furnace with a graphite heater and carbon felt
lining, the preforms were embedded in sacrificial undoped YAG
powders of 1 to 5 .mu.m particle size to prevent the samples from
being partially reduced to constituent metals due to strong
reducing atmosphere. Brownish sintered ceramic sheets were
reoxidized in a furnace under vacuum at 1400.degree. C. for 2 hrs
at heating and cooling rates of 10.degree. C./min and 20.degree.
C./min respectively.
Example 2.5
Optical Measurements
[0108] Chromaticity measurements were performed with Otsuka
Electronics MCPD 7000 multi channel photo detector system together
with required optical components such as optical fibers (Otuka
Electronics), 12-inch diameter integrating spheres (Gamma
Scientific, GS0IS12-TLS, calibration light source (Gamma
Scientific, GS-IS12-OP1) configured for total flux measurement, and
excitation light source (Cree blue-LED chip, dominant wavelength
455 nm, C455EZ1000-52001).
[0109] A blue LED with a peak wavelength of 455 nm was then placed
at the central position of the integrating sphere and was operated
with a drive current of 25 mA. First the radiation power from the
bare blue LED chip as excitation light was acquired. The light
emitting face distance of LED chip was 1 mm. A diced 2 mm.times.2
mm laminated sample was coated with paraffin oil having similar
refractive index as common encapsulation resin such as epoxy (for
example about 1.75) was then mounted a distance of about 100 .mu.m
from LED chip. The radiation power of the combination of the
composite laminate and the blue LED was then acquired.
[0110] As shown in FIG. 4, the composite YAG:Ce and Lu1 laminate,
which was prepared according to Examples 2.1-2.5, had CIE
coordinates with Cy of about 0.3986.+-.0.0025 and Cx of about
0.4328.+-.0.0025, indicating a white light having a CT of about
3025K ("warm white"). The resultant composite exhibited a CRI of
about 70. Meanwhile, FIG. 5 shows the emission spectrum the same
YAG:Ce and Lu1 laminate by a blue LED with a peak wavelength of 455
nm.
* * * * *