U.S. patent application number 13/802956 was filed with the patent office on 2013-08-08 for led module.
This patent application is currently assigned to Koninklijke Philips Electronics N.V.. The applicant listed for this patent is Koninklijke Philips Electronics N.V.. Invention is credited to Thomas DIEDERICH, Berno HUNSCHE, Hendrik Johannes Boudewijn JAGT, Hendrik Adrianus van SPRANG.
Application Number | 20130200416 13/802956 |
Document ID | / |
Family ID | 41057322 |
Filed Date | 2013-08-08 |
United States Patent
Application |
20130200416 |
Kind Code |
A1 |
van SPRANG; Hendrik Adrianus ;
et al. |
August 8, 2013 |
LED MODULE
Abstract
The present invention relates to a LED module which converts
pump light from a LED chip (120) to light at another wavelength,
which is emitted from the module. The conversion takes place in a
portion of a luminescent material (124). The color purity of the
LED module is enhanced by reducing any leakage of pump light using
a reflector in combination with an absorber. In one embodiment, the
absorber is integrated as one or several thin absorbing layers
between the layers of a multi-layer reflection filter (126); this
may yield an even higher reduction of pump light leakage from the
module.
Inventors: |
van SPRANG; Hendrik Adrianus;
(Waalre, NL) ; JAGT; Hendrik Johannes Boudewijn;
(Eindhoven, NL) ; HUNSCHE; Berno; (Langerwehe,
DE) ; DIEDERICH; Thomas; (Stolberg, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Koninklijke Philips Electronics N.V.; |
Eindhoven |
|
NL |
|
|
Assignee: |
Koninklijke Philips Electronics
N.V.
Eindhoven
NL
|
Family ID: |
41057322 |
Appl. No.: |
13/802956 |
Filed: |
March 14, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12994867 |
Nov 29, 2010 |
8410504 |
|
|
PCT/IB09/52264 |
May 29, 2009 |
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13802956 |
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Current U.S.
Class: |
257/98 |
Current CPC
Class: |
H01L 33/50 20130101;
H01L 2224/48091 20130101; H05B 33/22 20130101; H01L 2224/48247
20130101; H01L 2224/48091 20130101; H01L 2924/00014 20130101; H01L
33/44 20130101 |
Class at
Publication: |
257/98 |
International
Class: |
H01L 33/50 20060101
H01L033/50 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2008 |
EP |
08157943.5 |
Claims
1. A light source, comprising a LED chip for emitting excitation
light in a first wavelength range; a wavelength converter for
converting excitation light to converted light in a second
wavelength range; a multi-layer reflector for transmitting
converted light, and for reflecting excitation light onto the
wavelength converter, the reflector comprising a plurality of
alternating layers of at least two different materials having at
least two different indices of refraction; and an absorption layer,
arranged for absorbing unconverted excitation light and located
between layers of the multi-layer reflector.
2. The light source according to claim 1, wherein the wavelength
converter is located between the multi-layer reflector and the LED
chip.
3. The light source according to claim 2, wherein the multi-layer
reflector, the absorption layer, the wavelength converter and the
LED chip are joined to form a single stack.
4. The light source according to claim 1, wherein at least one
fourth of the total number of multi-layer reflector layers is
located on each side of the absorption layer.
5. The light source according to claim 1, wherein the multi-layer
reflector is parabolic.
6. The light source of claim 1, further comprising a separate
hemispherical absorber positioned around the luminescent wavelength
converter so that converted light from the luminescent wavelength
converter passes through the separate hemispherical absorber at a
normal angle of incidence and excitation light leaking through the
multi-layer reflector passes through the separate hemispherical
absorber at an oblique angle
7. The light source of claim 1, further comprising a lens enclosing
the LED chip, the luminescent wavelength converter and the
multi-layer reflector incorporating the absorption layer.
8. The light source of claim 7, wherein the lens is
hemispherical.
9. A light-emitting diode (LED) module comprising: a light-emitting
diode (LED) chip and a luminescent wavelength converter mounted
side by side on a sub-mount; a pair of electrical terminals
providing electrical current to the LED chip; a parabolic
multi-layer reflector incorporating an absorption layer; and a
hemispherical lens enclosing the LED chip, the luminescent
wavelength converter mounted side by side on the sub-mount and the
parabolic multi-layer reflector incorporating the absorption
layer.
10. The LED module of claim 9, wherein the LED chip emits
excitation light in a first wavelength range.
11. The LED module of claim 10, wherein the wavelength converter
converts excitation light to converted light in a second wavelength
range.
12. The LED module of claim 9, wherein the parabolic multi-layer
reflector comprises a plurality of alternating layers of at least
two different materials having at least two different indices of
refraction.
13. The LED module of claim 9, wherein the incorporated absorption
layer reduces the parabolic multi-layer reflector's transmission of
any excitation light impinging on the parabolic multi-layer
reflector at substantially oblique angles.
14. The LED module of claim 9, further comprising a separate
hemispherical absorber positioned around the luminescent wavelength
converter so that converted light from the luminescent wavelength
converter passes through the separate hemispherical absorber at a
normal angle of incidence and excitation light leaking through the
reflector parabolic multi-layer reflector passes through the
separate hemispherical absorber at an oblique angle.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a lightsource, comprising a
LED chip adapted for emitting excitation light in a first
wavelength range; a wavelength converter adapted for converting
excitation light to converted light in a second wavelength range;
and a reflector, adapted for transmitting converted light, and for
reflecting excitation light onto the wavelength converter.
BACKGROUND OF THE INVENTION
[0002] U.S. Pat. No. 7,245,072 B2 discloses a LED module comprising
a LED, a layer of a phosphor material, and a birefringent polymeric
multi-layer reflection filter. The phosphor material, which is
located between the reflection filter and the LED, emits visible
light when illuminated with ultraviolet (LTV) excitation light by
the LED, and the filter serves for removing remaining, unconverted
UV light from the optical output of the LED module. By using
birefringent polymers in the reflector layer, better filtering of
UV light having an oblique angle of incidence onto the filter is
reported.
[0003] The use of multiple birefringent layers in the reflector
however leads to complicated devices and/or fabrication
methods.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a less
complicated technique for removing excitation light from the light
output of a LED module. To this end, there is provided a
lightsource, comprising a LED chip adapted for emitting excitation
light in a first wavelength range; a wavelength converter adapted
for converting excitation light to converted light in a second
wavelength range; a reflector, adapted for transmitting converted
light, and for reflecting excitation light onto the wavelength
converter; and an absorption layer, arranged for absorbing
unconverted excitation light. The absorption layer assists in
decreasing the amount of emitted excitation light.
[0005] Preferably, the reflector is a multilayer reflector
comprising a plurality of alternating layers of at least two
different materials having at least two different indices of
refraction. Such reflectors may be given a high wavelength
selectivity at a substantially normal angle of incidence of the
light.
[0006] Preferably, the absorption layer is located between layers
of the reflector. This configuration may even further reduce the
amount of transmitted excitation light impinging on the reflector
at an angle of incidence that deviates from the reflection filter's
surface normal, and/or reduce the required number of process steps
in the fabrication of an efficient filter. More preferably, at
least one fourth of the total number of reflector layers is located
on each side of the absorber.
[0007] Preferably, the wavelength converter is located between the
reflector and the LED chip, as this configuration is beneficial
from a conversion efficiency point of view. Preferably, the
reflector, the absorption layer, the wavelength converter and the
LED chip are joined to form a single device. This is a very compact
and efficient configuration that is inexpensive to fabricate.
Preferably, the multi-layer reflector and the absorber have a total
thickness of less than 2000 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] This and other aspects of the present invention will now be
described in more detail, with reference to the appended drawings
showing a currently preferred embodiment of the invention.
[0009] FIG. 1 is a schematic sectional view of a LED module
comprising a LED chip, luminescent converter, a reflector and an
absorber.
[0010] FIG. 2 is a schematic sectional view of the LED and e
luminescent converter in FIG. 1.
[0011] FIG. 3 is a schematic sectional view of a LED module laving
the luminescent converter, reflector, and absorber integrated with
the LED chip.
[0012] FIG. 4 is a schematic sectional view of the LED in FIG.
3.
[0013] FIG. 5 is a graph, illustrating the transmittance of a
multi-layer reflector.
[0014] FIG. 6 is a graph, illustrating the transmittance of a
multi-layer reflector comprising an absorber layer.
[0015] FIG. 7 is a schematic sectional view of a LED module,
showing an alternative geometric configuration of the luminescent
converter and the reflector.
[0016] FIG. 8 is a schematic sectional view of the LED, the
luminescent converter, and the reflector in FIG. 7.
[0017] FIG. 9 is a schematic sectional view of a LED module,
showing yet another alternative geometric configuration of the
luminescent converter and the reflector.
[0018] FIG. 10 is a schematic sectional view of the LED and the
reflector in FIG. 9.
[0019] FIG. 11 is a schematic sectional view of a LED module,
showing still another alternative geometric configuration of the
luminescent converter and the reflector.
[0020] FIG. 12 is a schematic sectional view of the LED and the
reflector in FIG. 11.
DETAILED DESCRIPTION
[0021] Light emitting diodes, LEDs, are used her a wide variety of
applications. Often, a luminescent converter is integrated into the
LED module to create light of a different color than the light
originally emitted from the LED.
[0022] In order to obtain a pure color of the light emitted from a
LED module using luminescent conversion, it is important that no
excitation light be allowed to exit from the LED module. This is
particularly important in applications where the required color
temperature is specified by standards and regulations. To this end,
a filter is sometimes disposed in the LED module in order to filter
away any remaining excitation light from the LED module output.
[0023] FIG. 1 schematically illustrates an exemplary embodiment of
a LED module 10 comprising a LED 12. The LED 12 is fed with
electrical current via terminals 14, 16, and the output light of
the LED 12 is coupled out of the LED module 10 via an essentially
hemispherical lens 18. The LED is arranged to emit ultraviolet (UV)
light, and a phosphor layer 24 converts the UV light to white
light, i.e. to a mixture of red, green, and blue light. Total
conversion of the UV light is not achieved as the phosphor layer
would then have to be too thick, leading to a high re-absorption of
red, green, and blue light. Therefore, in order to reduce the
emission of UV light from the module 10, the lens 118 comprises a
reflector 26, which reflects UV light and transmits visible light.
A wavelength selective absorption layer 28 on the surface of the
lens significantly reduces any leakage of UV light. The wavelength
selectivity of the absorption layer 28 is such that its absorption
is higher in the UV wavelength range than in the visible wavelength
range. Throughout this disclosure, an absorption layer is defined
as a layer consisting of material(s) having an extinction
coefficient k>0.005 in the excitation wavelength range. An
absorption layer is intended to be located in the light path from
the light emitting surface of the LED chip and/or the luminescent
converter, to the LED module tight output surface; structures such
as electrical wiring, opaque LED chip submounts or the like are not
considered absorber layers in this sense.
[0024] FIG. 2 shows the LED 12 and the phosphor layer 24 of FIG. 1
more in detail. A LED chip 20 is located on a submount 22.
Electrical current is fed to the top electrode of the LED chip 20
through a wire 30.
[0025] FIG. 3 schematically illustrates an exemplary embodiment of
a LED module 110 comprising a LED 112.
[0026] FIG. 4 shows the LED 112 of FIG. 3 more in detail. A LED
chip 120 is flip-chip mounted onto a submount 122. Electrical
current is fed to the top electrode of the LED chip 120 through a
conductor 130 in a via-hole. The LED chip 120 emits blue excitation
light in the wavelength range 400-470 nm, with a peak wavelength of
about 450 nm. The excitation light is converted to amber light at
about 600 nm by a luminescent phosphor material layer 124 attached
to or deposited on the LED chip 120; in this particular example,
the phosphor material is a LUMIRAMIC.RTM. comprising
(BaSr).sub.2Si.sub.5N.sub.8:Eu, i.e. Barium Strontium Silicon
Nitride doped with Europium. Its emission wavelength characteristic
may be varied by changing the ratio between Barium and Strontium;
in this case, 85% Ba and 15% Sr is used. On top of the
LUMIRAMIC.RTM. layer 124, there is a multi-layer reflector coating
126, which incorporates an absorbing layer. Locating the reflector
directly on the LUMIRAMIC.RTM. layer has the advantage of
reflecting back a larger portion of the unconverted excitation
light onto the LUMIRAMIC.RTM. layer, and thus increasing the
conversion efficiency.
[0027] A multi-layer reflector is a type of interference filter
that consists of several alternating layers having different
indices of refraction; their wavelength response can be designed
relatively freely, and they can be designed to give a high
suppression of the excitation light. Multi-layer reflectors are
therefore very well suited for removing excitation light from the
LED module output.
[0028] However, as the transparency of a typical interference
filter coating varies with the angle of incidence of the light
impinging on the interference filter coating, some excitation light
will leak through the filter due to the fact that LEDs and
wavelength converters typically do not produce a collimated
output.
[0029] Table 1 gives an example of the structure of a multi-layer
reflector that is not provided with an internal absorber layer; its
corresponding transmittance as a function of angle of incidence,
relative to the reflector surface normal, is given in FIG. 5. The
filter is made up of alternating layers of SiO.sub.2, having a
refractive index of approx. 1.46, and Nb.sub.2O.sub.5, with a
refractive index of approx. 2.39. Layer no. 1 is adjacent to a
LUMIRAMIC.RTM.
TABLE-US-00001 TABLE 1 Layer Material d (nm) 1 Nb.sub.2O.sub.5
22.43 2 SiO.sub.2 47.46 3 Nb.sub.2O.sub.5 58.51 4 SiO.sub.2 37.19 5
Nb.sub.2O.sub.5 56.08 6 SiO.sub.2 58.00 7 Nb.sub.2O.sub.5 167.17 8
SiO.sub.2 61.99 9 Nb.sub.2O.sub.5 163.83 10 SiO.sub.2 62.79 11
Nb.sub.2O.sub.5 164.02 12 SiO.sub.2 86.66 13 Nb.sub.2O.sub.5 31.59
14 SiO.sub.2 86.17 15 Nb.sub.2O.sub.5 38.59 16 SiO.sub.2 78.94 17
Nb.sub.2O.sub.5 56.06 18 SiO.sub.2 32.39 19 Nb.sub.2O.sub.5 81.56
20 SiO.sub.2 39.43 21 Nb.sub.2O.sub.5 179.54 22 SiO.sub.2 55.61 23
Nb.sub.2O.sub.5 164.17 24 SiO.sub.2 67.07 25 Nb.sub.2O.sub.5 162.12
26 SiO.sub.2 60.98 27 Nb.sub.2O.sub.5 74.36 28 SiO.sub.2 21.77 29
Nb.sub.2O.sub.5 63.28 30 SiO.sub.2 52.35 31 Nb.sub.2O.sub.5 295.69
32 SiO.sub.2 51.12 33 Nb.sub.2O.sub.5 159.13 34 SiO.sub.2 71.99 35
Nb.sub.2O.sub.5 154.03 36 SiO.sub.2 72.77 37 Nb.sub.2O.sub.5 153.48
38 SiO.sub.2 63.71 39 Nb.sub.2O.sub.5 146.28 40 SiO.sub.2 77.15 41
Nb.sub.2O.sub.5 5.71 Total Thickness 3583.18
converter, and layer no. 41 is adjacent to a lens having a
refractive index of about 1.5; d signifies the thickness of each
layer in nanometers.
[0030] Table 2 gives an example of the structure of the multi-layer
reflector 126 of the LED module described above with reference to
FIGS. 2-3, wherein the filter incorporates an integrated absorber
layer of Fe.sub.2O.sub.3. The filter's transmittance as a function
of angle of incidence is given in FIG. 6. Layer no. 1 is adjacent
to the LUMIRAMIC.RTM. converter 124 and layer no. 17 is adjacent to
the lens 18, which consists of SiO.sub.2. Note that the thickness
of the reflection filter is approximately one third of the
thickness of the reflection filter of table it. Also, the absorber
layer is an integral part of the reflector and contributes to the
reflective properties of the device, since Fe.sub.2O.sub.3 has an
index of refraction of 3.11, significantly different from the index
of refraction of the adjacent Nb.sub.2O.sub.5 layers. The
reflection filter multilayer structure surrounding the thin
absorbing Fe.sub.2O.sub.3 layer, on the other hand, enhances the
absorption of the thin Fe.sub.2O.sub.3 layer.
TABLE-US-00002 TABLE 2 Layer Material d (nm) 1 Nb.sub.2O.sub.5
149.61 2 SiO.sub.2 46.59 3 Nb.sub.2O.sub.5 162.56 4 SiO.sub.2 59.38
5 Nb.sub.2O.sub.5 160.02 6 SiO.sub.2 62.68 7 Nb.sub.2O.sub.5 78.00
8 Fe.sub.2O.sub.3 8.40 9 Nb.sub.2O.sub.5 80.66 10 SiO.sub.2 64.37
11 Nb.sub.2O.sub.5 46.08 12 SiO.sub.2 72.79 13 Nb.sub.2O.sub.5
31.75 14 SiO.sub.2 95.16 15 Nb.sub.2O.sub.5 44.42 16 SiO.sub.2
53.56 17 Nb.sub.2O.sub.5 31.17 Total Thickness 1247.19
[0031] The significant difference between the angular dependencies
of the two filters of the graphs in FIGS. 5-6 is impressive. By
integrating only a thin layer of an absorber into the filter, the
filter can not only be made thinner and fabricated using fewer
process steps; also the angular dependency of the transmittance of
blue light is significantly reduced, and higher-order transmission
spikes at tow angles are removed.
[0032] FIG. 7 schematically illustrates an exemplary embodiment of
a LED module 210 comprising a LED 212 and a separate
phosphor/reflector/absorber portion 224/226. The configuration of
the LED 212 and the phosphor/reflector/absorber portion is
illustrated more in detail in FIG. 8, which shows a multi-layer
reflector 226, comprising a plurality of transparent, alternating
reflector layers and a plurality of integrated absorber layers
deposited onto a layer of phosphor 224.
[0033] FIGS. 9 and 10 illustrate an alternative geometry of the LED
module, wherein the LED chip 320 and the luminescent converter 324
are mounted side by side on a submount 322. Excitation light from
the LED chip is reflected onto the luminescent converter 324 by an
essentially parabolic multi-layer reflector 326, which also
incorporates an absorber layer. The reflector 326 is arranged to
transmit the converted light from the luminescent converter, and
the absorption layer reduces the reflector's 326 transmission of
any excitation light impinging on the reflector 326 at
substantially oblique angles.
[0034] The geometric separation of the LED chip 320 and the
luminescent converter 324 also makes it possible to locate and
extend a separate hemispherical absorber (not shown) around the
luminescent converter, such that converted light from the
luminescent converter will pass through the separate absorber at a
normal angle of incidence, and excitation light leaking through the
reflector will pass through the separate absorber at an oblique
angle. This will mike the path through the absorber longer for the
excitation light than for the converted light.
[0035] FIGS. 11 and 12 show an embodiment illustrating how a
geometric separation of the LED chip from the luminescent converter
may enable different absorption levels of excitation light and
converted light, respectively, and thereby contribute to improving
the colour temperature of a LED module. A wavelength selective
reflector 426 reflects the light from a LED chip 420 onto a
luminescent converter 424. Converted lightfrom the luminescent
converter passes through the reflector, and then through an
absorber 428 at a normal angle of incidence. Any excitation light
from the LED chip 420 that may leak through the wavelength
selective reflector 426 will pass through the absorber 428 at an
oblique angle. This will make the path through the absorber 428
longer for the excitation light than for the converted light.
[0036] In summary, the invention relates to a LED module which
converts pump light from a LED chip to light at another wavelength,
which is emitted from the module. The conversion takes place in a
portion of a luminescent material. The color purity of the LED
module is enhanced by reducing any leakage of pump light using a
reflector in combination with an absorber. In one embodiment, the
absorber is integrated as one or several thin absorbing layers
between the layers of a multi-layer interference filter; this may
yield an even higher reduction of pump light leakage from the
module.
[0037] The person skilled in the art realizes that the present
invention by no means is limited to the preferred embodiments
described above. On the contrary, many modifications and variations
are possible within the scope of the appended claims. For example,
the invention is not limited to absorption layers of
Fe.sub.2O.sub.3; also other materials featuring an absorption in
the excitation wavelength range may be used, for example but not
limited to zinc iron oxide, titanium iron oxide, vanadium oxide,
bismuth oxide, copper oxide, bismuth vanadate, zirconium
praseodymium silicate, or any mixture thereof.
[0038] Neither is the invention limited to luminescent layers of
LUMIRAMIC.RTM. or other phosphorescent materials; any atomic or
molecular species or solid-state compounds that convert at least a
part of incident electromagnetic radiation to electromagnetic
radiation with a characteristic signature may be used, such as
fluorescent dyes or luminescent quantum dots.
[0039] In the examples above, the multi-layer reflectors comprise
alternating layers of Nb.sub.2O.sub.5 and SiO.sub.2. Other
combinations of two or more different materials, having different
indices of refraction, may be used and are covered by the appended
claims. Further, the reflector is not limited to multi-layer
reflectors; any type of wavelength selective reflector capable of
reflecting the excitation wavelength while at the same time
transmitting the converted wavelength may be used. The absorber may
consist of one or several absorbing layers integrated in the
reflector, or it may be a separate absorber located elsewhere in
the LED module. Even though the entire LED module preferably is
comprised in a single housing, it may also be divided between
separate housings. Different parts of the device may be separated
between different modules, which, when cooperating, obtain the same
function as claimed. Further, even though in the examples above,
blue or UV light is used to generate amber or white light, other
combinations are also covered by the appended claims. The invention
is not limited to LED chips or luminescent converters emitting
visible light; they may as well emit in the IR and UV regions. Nor
is the invention limited to LED:s emitting excitation light in a
broadband optical spectrum. Also narrow-band LED:s incorporating
any type of optical feed-back and stimulated emission, such as
diode lasers, are within the scope of the claim. Features disclosed
in separate embodiments in the description above may be
advantageously combined.
[0040] The use of the indefinite article "a" or "an" in this
disclosure does not exclude a plurality. Any reference signs in the
claims should not be construed as limiting the scope.
* * * * *