U.S. patent application number 14/618406 was filed with the patent office on 2015-06-11 for led assembly.
The applicant listed for this patent is KONINKLIJKE PHILIPS N.V.. Invention is credited to HANS-HELMUT BECHTEL, THOMAS DIEDERICH, MATTHIAS HEIDEMANN, PETER JOSSEF SCHMIDT.
Application Number | 20150162503 14/618406 |
Document ID | / |
Family ID | 42035569 |
Filed Date | 2015-06-11 |
United States Patent
Application |
20150162503 |
Kind Code |
A1 |
BECHTEL; HANS-HELMUT ; et
al. |
June 11, 2015 |
LED ASSEMBLY
Abstract
A light emission diode (LED) assembly, comprising a LED die
(10), a phosphor layer (12), and a filter layer (14), wherein said
filter layer (14) is developed in such a manner that light rays
with a wavelength of about 400 nm to 500 nm, preferably of about
420 nm to 490 nm, emitted from the LED die (10) are at least
partially reflected depending on their emission angle to the normal
on the filter layer (14). With the inventive LED assembly it is
possible to provide a LED assembly which solves the yellow ring
problem without a reduction of the efficiency of the LED
assembly.
Inventors: |
BECHTEL; HANS-HELMUT;
(EINDHOVEN, NL) ; HEIDEMANN; MATTHIAS; (EINDHOVEN,
NL) ; SCHMIDT; PETER JOSSEF; (EINDHOVEN, NL) ;
DIEDERICH; THOMAS; (EINDHOVEN, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KONINKLIJKE PHILIPS N.V. |
EINDHOVEN |
|
NL |
|
|
Family ID: |
42035569 |
Appl. No.: |
14/618406 |
Filed: |
February 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13131384 |
May 26, 2011 |
8957439 |
|
|
PCT/IB09/55380 |
Nov 27, 2009 |
|
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14618406 |
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Current U.S.
Class: |
257/98 |
Current CPC
Class: |
H01L 33/60 20130101;
H01L 2924/12041 20130101; H01L 33/46 20130101; H01L 33/50 20130101;
H01L 2924/12041 20130101; H01L 24/32 20130101; H01L 33/58 20130101;
H01L 2924/00 20130101 |
International
Class: |
H01L 33/50 20060101
H01L033/50; H01L 33/60 20060101 H01L033/60; H01L 33/58 20060101
H01L033/58 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 2, 2008 |
EP |
08170458.7 |
Claims
1. A device comprising: a light emitting diode that emits first
light; a color converter that is stimulated by the first light to
emit second light; and a filter that reflects 10% to 50% of the
first light emitted at angles between 0.degree. and 40.degree. and
fully transmits first light emitted at larger angles.
2. The device of claim 1 wherein the first light comprises light
with a wavelength between 400 nm and 500 nm.
3. The device of claim 1 wherein the color converter comprises a
phosphor.
4. The device of claim 1 wherein the filter comprises a dielectric
structure comprising alternating low refractive index and high
refractive index materials.
5. The device of claim 4 wherein the low refractive index materials
have a refractive index between 1.2 and 1.8 and the high refractive
index materials have a refractive index between 1.6 and 3.
6. The device of claim 4 wherein the low index material comprises
Nb.sub.2O.sub.5 and the high refractive index material comprises
SiO.sub.2.
7. The device of claim 1 wherein the rest of the first light
emitted at angles between 0.degree. and 40.degree. is transmitted
by the filter without reflection.
8. A device comprising: a light emitting diode that emits first
light; a color converter that is stimulated by the first light to
emit second light; and a filter that partially reflects the first
light emitted at angles between 0.degree. and 30.degree. and fully
transmits the first light emitted at angles between 30.degree. and
90.degree..
9. The device of claim 8 wherein the first light is blue and the
second light is yellow.
10. The device of claim 8 wherein the filter is disposed between
the light emitting diode and the color converter.
11. The device of claim 8 wherein the color converter is disposed
between the light emitting diode and the filter.
12. The device of claim 8 wherein the color converter is a first
phosphor layer, the device further comprising a second phosphor
layer, wherein the filter is disposed between the first phosphor
layer and the second phosphor layer.
13. The device of claim 8 wherein the color converter comprises a
luminescent ceramic.
14. The device of claim 8 wherein the color converter comprises a
phosphor embedded in a transparent matrix material.
15. A device comprising: a light emitting diode that emits blue
light; a phosphor layer disposed in a path of the blue light,
wherein the phosphor layer is stimulated by the blue light to emit
yellow light; and a filter that reflects a portion of the blue
light such that the blue light and the yellow light have the same
ratio over emission angles from 0.degree. to 90.degree..
16. The device of claim 15 wherein the filter reflects 10% to 50%
of the blue light.
17. The device of claim 15 wherein blue light at an emission angle
near normal is reflected by the filter more than blue light at an
emission angle far from normal.
18. The device of claim 15 wherein the filter comprises alternating
low refractive index and high refractive index materials.
19. The device of claim 18 wherein the filter comprises nine layers
of low refractive index material and nine layers of high refractive
index material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/131,384, filed May 26, 2011, to be issued
as U.S. Pat. No. 8,957,439 on Feb. 17, 2015, which is a 371(c)
national stage entry of PCT/IB09/55380 filed on Nov. 27, 2009,
which is the international application of EP 08170458.7 filed on
Dec. 2, 2008. U.S. Pat. No. 8,957,439 and EP 08170458.7 are
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to the field of light emission diode
(LED) assemblies. Particularly the invention relates to enhanced
emission phosphor-converting LED light assemblies (pcLED). Such
assemblies are often employed to provide white light.
BACKGROUND OF THE INVENTION
[0003] White light emitting LEDs generally comprise a blue emitting
LED combined with a phosphor layer that is stimulated by the blue
emission of the LED into emitting yellow light, the combination of
the yellow and blue emissions providing a white light. For normal
direction, vertical to the surface of the LED die or vertical to
the surface of the phosphor layer with an emission angle of
0.degree., the path length in the phosphor layer of the light rays
emitted by the blue emitting LED is equal to the thickness of the
phosphor layer. For increasing emission angles the path length for
blue light rays increases. Accordingly the fraction of absorbed
blue light rays by the phosphor layer is lower for the light rays
with an emission angle of 0.degree. than for the light rays with an
increasing emission angle. Since the converted light emitted by the
phosphor layer always has a Lambertian over angle distribution, the
white light emitted by the LED has a higher correlated colour
temperature for normal emission with an emission angle of about
0.degree.. Generally, the phosphor layer is a
Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (YAG:Ce). In case of such a
YAG:Ce phosphor layer emitted light becomes yellowish with
increasing emission angle, perceived as yellow ring. To solve the
yellow ring problem it is known to increase the scattering power of
the phosphor layer and/or to add a scattering layer on top of the
phosphor layer. For both, the reduction of the yellow ring problem
results in a reduction of the LED efficiency, since scattering is
accompanied by light reflection leading to light losses. In
particular, scattering of the down-converted phosphor emission
leads to reflection with accompanied reflection losses.
SUMMARY OF THE INVENTION
[0004] Its is an object of the invention to provide a light
emission diode (LED) assembly which solves the above stated yellow
ring problem without a reduction of the efficiency of the LED
assembly.
[0005] The light emission diode (LED) assembly according to the
invention comprises a LED die, a phosphor layer, and a filter
layer, wherein said filter layer is developed in such a manner that
light rays with a wavelength of about 400 nm to 500 nm, preferably
of about 420 nm to 490 nm, emitted from the LED die are at least
partially reflected depending on their emission angle to the normal
on the filter layer.
[0006] The LED die is preferably a blue emitting LED. The phosphor
layer is preferably Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ (YAG:Ce). The
filter layer is preferably a dielectric filter layer. This filter
layer realises a full transmission for light rays emitted by the
LED die independently from their wavelength within the visible
range for large emission angles, preferably emission angle between
30.degree. to 90.degree., to the normal of the filter. For smaller
emission angles, preferably emission angles between 0.degree. to
30.degree. to the normal on the filter layer, partial reflections
of the light rays with a wavelength of about 400 nm to 500 nm are
provided. Light rays with a wavelength of about 400 nm to 500 nm
are blue light rays emitted by the LED die. The partial reflections
of the blue light rays emitted by the LED die depending on their
emission angle to the normal on the filter layer realizes a uniform
over angle emission without loss of efficiency of the light emitted
by LED. The normal on the filter layer is along the axis vertical
to the plain surface of the filter layer.
[0007] For uniform white light emitted by the LED die the emitted
intensity ratio of directly emitted light from the LED die and
converted light from the phosphor layer has to be constant under
all angles. Usually light emitted by the LED provides a
cudgel-shaped form in the area of small emission angle, preferably
an emission angle of about 0.degree. to 30 .degree. to the normal
on the filter layer. However, the yellow light emitted by the LED
die usually provides a ball-shaped form over the whole emission
angle of about 0.degree. to 90.degree.. Thus, there are areas,
especially at larger emission angles, preferably between 30.degree.
to 90.degree. where the ratio of blue light to yellow light
decreases. Emissions under these angles cause the yellow ring
problem. By reflection of a certain amount of the blue light for
small emission angles of about 0.degree. to 30.degree. it is
possible to transform the cudgel-shaped form of the blue light into
a ball-shaped form so that the blue light and the yellow light have
the same ratio over the whole emission angle from 0.degree. to
90.degree.. Thus, a superposition of yellow light and blue light
over the whole emission angle is obtained so that uniform white
light is emitted by the LED assembly over the whole emission angle
without a yellow ring problem.
[0008] Preferably, the filter layer reflects the light rays with an
emission angle of about 0.degree. to 30.degree., preferably of
about 0.degree. to 20.degree., to the normal on the filter layer.
The reflected light rays are blue light rays of the emitted light
of the LED die with a wavelength of about 400 nm to 500 nm,
preferably of about 420 nm to 490 nm.
[0009] In a preferred embodiment of the invention about 10% to 50%,
preferably of about 15% to 30%, of the light rays emitted by the
LED die are reflected by the filter layer depending on their
emission angle. The reflected light rays are blue light rays of the
emitted light of the LED die with a wavelength of about 400 nm to
500 nm, preferably of about 420 nm to 490 nm. Thus, about 10% to
50%, preferably 15% to 40%, of the blue light rays emitted by the
LED with an emission angle of about 0.degree. to 40.degree.,
preferably of about 0.degree. to 30.degree., to the normal on the
filter layer are reflected. The rest of the blue light rays emitted
by the LED with an emission angle of about 0.degree. to 40.degree.,
preferably of about 0.degree. to 30.degree., pass the filter layer
without a reflection.
[0010] The filter layer comprises preferably a dielectric layer
coating of alternating low and high refractive index materials. The
alternating low and high refractive index materials may be chosen
in such a manner that a well directed reflection of the blue light
emitted by the LED die can be achieved.
[0011] The materials of the dielectric coating layer are preferably
transparent for wavelength between 400 nm and 800 nm with a
refractive index of the high refractive index materials in the
range of 1.6 to 3 and with a refractive index of the low refractive
index materials in the range of 1.2 to 1.8. The absorption
coefficient of the index materials is <0.00001 for
wavelength>480 nm and <0.003 for wavelength>400 nm.
Nb.sub.2O.sub.5 (nobium oxide) is preferably used as high
refractive index material and SiO.sub.2 (silicon oxide) is
preferably used as low refractive index material.
[0012] Preferably, the filter layer comprises nine layers of the
high refractive index materials and nine layers of the low
refractive index materials. The layers may be applied by thin film
deposition techniques like chemical vapour deposition or
sputtering.
[0013] According to a preferred embodiment of the invention, the
filter layer is arranged between the LED die and the phosphor
layer. Thus, the filter layer is positioned on top of the LED die
and the phosphor layer is positioned on top of the filter
layer.
[0014] Due to another embodiment of the invention, the phosphor
layer is arranged on top of the LED die and the filter layer is
arranged on top of the phosphor layer.
[0015] Additionally, it is possible according to a further
embodiment of the invention, to provide a LED assembly with a first
phosphor layer and a second phosphor layer, wherein the filter
layer is arranged between the first phosphor layer and the second
phosphor layer. Preferably, the first phosphor layer is positioned
on top of the LED die.
[0016] The phosphor layer may comprise a Lumiramic plate and/or
phosphor powder embedded in a transparent matrix material. The
Lumiramic plate is a poly-crystalline ceramic plate of Ce (III)
doped yttrium gadolinium garnet (Y, GdAG:Ce). To combine such a
Lumiramic plate with a blue light emitting LED die to produce white
light in the range of 5000 K correlated color temperature is very
advantageously. Scattering and light extraction means of the
Lumiramic ceramic color converter plates enable production of
reliable and efficient white pcLEDs. Measurement of the optical
properties of the Lumiramic plates before the final LED assembly
allows pick and place packaging with exact targeting of the desired
white color point of the LED.
[0017] Preferably, the LED assembly may provide a transparent glass
plate which functions as a substrate for the filter layer. Thus,
the filter layer does not have to be applied directly on the LED
die or the phosphor layer. The filter layer can be easily applied
to the transparent glass plate and after applying the filter layer
on the glass plate it is arranged to the LED assembly.
[0018] According to a preferred embodiment of the invention, the
filter layer has a total thickness of 750 nm to 950 nm, preferably
of about 800 nm to 900 nm.
[0019] Further, according to an embodiment of the invention, the
phosphor layer has a thickness of about 80 .mu.m to 150 .mu.m,
preferably of about 100 .mu.m to 130 .mu.m.
[0020] Moreover, the layers of high refractive index materials
preferably vary in thickness from 5 nm to about 70 nm and the
layers of low refractive index materials preferably vary in
thickness from about 20 nm to about 300 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiments described
hereinafter.
[0022] In the drawings:
[0023] FIG. 1 is a schematic view of a first embodiment of a light
emitting diode assembly according to the invention;
[0024] FIG. 2 is a graph showing the transmittance of the inventive
filter layer depending on the emission angle and the wavelength of
the light emitted by the LED die;
[0025] FIG. 3 is a graph showing geometrical distance of color
coordinates to the color coordinates in normal emission in Uniform
Color Space (CIE 1976) of a white LED assembly;
[0026] FIG. 4 is a schematic view of a second embodiment of a light
emitting diode assembly according to the invention; and
[0027] FIG. 5 is a schematic view of a third embodiment of a light
emitting diode assembly according to the invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0028] FIG. 1 shows a first embodiment of a light emission diode
(LED) assembly according to the invention with a LED die 10, a
phosphor layer 12 and a filter layer 14. The led die 10, the
phosphor layer 12 and the filter 14 are preferably covered by a
semicircle-shaped housing 16 that can have a reflecting coating
applied to the interior wall thereof. The LED die 10 that emits
blue light with a wavelength of about 400 nm to 500 nm is
positioned at the bottom 18 of the LED assembly. On the top of the
LED die 10 the phosphor layer 12 is positioned. The phosphor layer
12 emits yellow light with a wavelength of about 570 nm to 590 nm.
The phosphor layer 12 may comprise a Lumiramic plate and/or a
phosphor powder embedded in a transparent matrix material. The
thickness of the phosphor layer 12 is about 100 .mu.m to 120 .mu.m.
On the top of the phosphor layer 12 the filter layer 14 is
positioned. The filter layer 12 comprises a dielectric layer
coating of alternating low and high reflective index materials,
like Nb.sub.2O.sub.5 and SiO.sub.2.
[0029] FIG. 2 shows a graph showing the transmittance of the
inventive filter layer 14 depending on the emission angle and the
wavelength of the light emitted by the LED die 10. The filter layer
14 shown in this graph has a layer construction shown in the
following table 1:
TABLE-US-00001 TABLE 1 Layer Material Thickness [nm] 1
Nb.sub.2O.sub.5 15.04 2 SiO.sub.2 40.81 3 Nb.sub.2O.sub.5 19.95 4
SiO.sub.2 62.79 5 Nb.sub.2O.sub.5 11.03 6 SiO.sub.2 554.43 7
Nb.sub.2O.sub.5 1.32 8 SiO.sub.2 101.21 9 Nb.sub.2O.sub.5 13.57 10
SiO.sub.2 76.41 11 Nb.sub.2O.sub.5 19.62 12 SiO.sub.2 58.04 13
Nb.sub.2O.sub.5 15.14 14 SiO.sub.2 72.37 15 Nb.sub.2O.sub.5 15.13
16 SiO.sub.2 97.54 17 Nb.sub.2O.sub.5 12.78 18 SiO.sub.2 90.31 19
Nb.sub.2O.sub.5 7.44 20 SiO.sub.2 66.31 21 Nb.sub.2O.sub.5 3.68
[0030] The different lines shown in the graph are the different
emission angles 0.degree., 26.degree.; 40.degree. and 77.degree..
As it can be seen, for large emission angles, like 40.degree. and
77.degree., light rays independent from its wavelength are able to
pass the filter layer 14 without any reflection or absorption. At
this emission angle the transmission of the emitted light rays,
especially the blue emitted light rays, is about 100%. For small
emission angles, like 0.degree. and 26.degree., blue light rays
with a wavelength of 400 nm to 500 nm are not completely able to
pass the filter layer. At this emission angle the transmission of
the emitted light rays is about 80%. About 20% of the blue light
rays are reflected by the filter layer 14. The yellow light rays of
the phosphor layer 12 with a wavelength of about 520 nm to 650 nm
are fully able to pass the filter layer independent from the
emission angle. Thus, the filter layer 14 only reflects some of the
blue emitted light rays. The partial reflections of blue light rays
emitted by the LED die 10 depending on their emission angle to the
normal on the filter layer 14 realizes a uniform over angle
emission without loss of efficiency of the light emitted by the LED
die 10, because blue light reflected at the filter layer is
absorbed by the phosphor layer and converted to phosphor
emission.
[0031] The filter layer 14 can also have the layer construction
shown in the following table 2:
TABLE-US-00002 TABLE 2 Layer Material Thickness [nm] 1
Nb.sub.2O.sub.5 25.85 2 SiO.sub.2 33.7 3 Nb.sub.2O.sub.5 29.11 4
SiO.sub.2 36.26 5 Nb.sub.2O.sub.5 11.19 6 SiO.sub.2 35.9 7
Nb.sub.2O.sub.5 11.91 8 SiO.sub.2 95.52 9 Nb.sub.2O.sub.5 14.5 10
SiO.sub.2 114.43 11 Nb.sub.2O.sub.5 22.39 12 SiO.sub.2 50.5 13
Nb.sub.2O.sub.5 32.33 14 SiO.sub.2 27.98 15 Nb.sub.2O.sub.5 31.87
16 SiO.sub.2 68.13 17 Nb.sub.2O.sub.5 12.63 18 SiO.sub.2 203.49
[0032] FIG. 3 shows the geometrical distance of color coordinates
to the color coordinates in normal emission in Uniform Color Space
(CIE 1976) of a white LED assembly without (full line) and with
(dashed line) an inventive filter layer depending from the emission
angle of the emitted light rays. As it can be seen in the graph,
with the inventive filter layer 14 it is possible to obtain an
almost constant color of the light rays emitted of the LED assembly
independent from the emission angle of the light rays.
[0033] FIG. 4 shows a schematic view of a second embodiment of a
light emitting diode assembly according to the invention. In this
embodiment the filter layer 14 is arranged between the LED die 10
and the phosphor layer 12.
[0034] FIG. 5 shows a schematic view of a third embodiment of a
light emitting diode assembly according to the invention, whereas
the LED assembly comprises a first phosphor layer 12 and a second
phosphor layer 20. The filter layer 14 is arranged between the
first phosphor layer 12 and the second phosphor layer 20, whereas
the first phosphor layer 12 is positioned on top of the LED die
10.
[0035] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive, the invention is not limited to the disclosed
embodiments.
[0036] Other variations to the disclosed embodiments can be
understood and effected by those skilled in the art in practicing
the claimed invention, from a study of the drawings, the
disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. The
mere fact that certain measures are recited in mutually different
dependent claims does not indicate that a combination of these
measures cannot be used to advantage. Any reference signs in the
claims should not be construed as limiting the scope.
* * * * *