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WO2012120433A1 - Phosphor composition for leds - Google Patents

Phosphor composition for leds Download PDF

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Publication number
WO2012120433A1
WO2012120433A1 PCT/IB2012/051018 IB2012051018W WO2012120433A1 WO 2012120433 A1 WO2012120433 A1 WO 2012120433A1 IB 2012051018 W IB2012051018 W IB 2012051018W WO 2012120433 A1 WO2012120433 A1 WO 2012120433A1
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WIPO (PCT)
Prior art keywords
phosphor
systems
doped
composition according
iii
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Application number
PCT/IB2012/051018
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French (fr)
Inventor
Peter Josef Schmidt
Matthias Heidemann
Andreas TÜCKS
Hans-Helmut Bechtel
Original Assignee
Koninklijke Philips Electronics N.V.
Philips Intellectual Property & Standards Gmbh
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Publication of WO2012120433A1 publication Critical patent/WO2012120433A1/en

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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7766—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing two or more rare earth metals
    • C09K11/7774—Aluminates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/0883—Arsenides; Nitrides; Phosphides
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/7729—Chalcogenides
    • C09K11/7731—Chalcogenides with alkaline earth metals
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/77342—Silicates
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/77347—Silicon Nitrides or Silicon Oxynitrides
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/77348—Silicon Aluminium Nitrides or Silicon Aluminium Oxynitrides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/48—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor body packages
    • H01L33/50—Wavelength conversion elements
    • H01L33/501—Wavelength conversion elements characterised by the materials, e.g. binder
    • H01L33/502—Wavelength conversion materials
    • H01L33/504—Elements with two or more wavelength conversion materials

Definitions

  • the present invention relates to the field of light emission diodes (LED). Particularly the invention relates to enhanced uniform emission phosphor-converting LED light assemblies (pcLED) and efficient manufacturing of the same.
  • LED light emission diodes
  • pcLED enhanced uniform emission phosphor-converting LED light assemblies
  • a phosphor composition for a LED comprising at least one Ce (III) doped phosphor and at least one Eu (II) doped phosphor whereby
  • the Ce(III) doped phosphor has a lowest lying 4f ⁇ 5d absorption band that peaks in the range > 440 to ⁇ 480 nm and has a spectral width (FWHM, full width at half maximum) in the range of > 2000 to ⁇ 4300 cm "1 ,
  • the Ce(III) doped phosphor has an emission band peaking in the range > 510 to ⁇ 570 nm
  • the Eu (II) doped phosphor has an emission band peaking in the range > 490 to ⁇ 570 nm; and whereby at least one absorption coefficient k in the range of 420 to 450 nm of the Eu(II) doped phosphor is 50% of the absorption coefficient k' at 380 nm.
  • LEDs can be manufactured, showing an extremely stable color point (usually a white color point, but this is not limiting: the invention can be used with LEDs to form other colors points as well) that is only slightly shifted by variations of the blue pump emission wavelength and thus shows significantly higher temperature and drive stability in combination with increased production yields.
  • an extremely stable color point usually a white color point, but this is not limiting: the invention can be used with LEDs to form other colors points as well
  • the LED color point also becomes a lot more stable as a function of temperature and drive current of the LED.
  • inventive phosphors are especially advantageous for applications which are designed for wafer level LED manufacturing where blue binning needs to be skipped.
  • the invention can be applied using conventional manufacturing techniques and avoiding sophisticated layouts of the production process.
  • a complete wafer of LEDs with typically a (blue) peak emission in the range of 430 to 470 nm can be manufactured with a single thickness of the phosphor layer, showing an extremely stable color point within a 7-step McAdam ellipses lying within one nominal CCT Category, as defined by ANSI NEMA ANSLG C78.377-2008 American National Standard for Electric Lamps— Specifications for the Chromaticity of Solid State Lighting Products.
  • the Ce(III) doped phosphor has a lowest lying 4f ⁇ 5d absorption band which has a spectral width (FWHM, full width at half maximum) in the range of > 2400 to ⁇ 4000 cm "1 .
  • the sum of the absorption coefficients of said lowest lying 4f ⁇ 5d absorption bands of (i) the Eu(II) doped phosphor and (ii) the Ce(III) doped phosphor has a minimum in the range > 380 to ⁇ 450 nm.
  • the Ce(III) doped phosphor has a smaller CIE 1931 y color coordinate and/or a smaller x color coordinate than the Eu(II) doped phosphor.
  • the difference in y color coordinate is > 0.01, preferably > 0.05 and most preferred > 0.07.
  • the difference in x color coordinate is > 0.02, preferably > 0.08 and most preferred > 0.13.
  • the Eu (II) doped phosphor has a lowest lying 4f ⁇ 5d absorption band in the spectral range > 300 to ⁇ 520, preferably 460, more preferred ⁇ 430 nm.
  • the lowest lying absorption band maximum of the Eu(II) doped phosphor is located at higher energies compared to the lowest lying absorption band maximum of the Ce(III) doped phosphor.
  • the at least one Ce(III) doped phosphor comprises a garnet material.
  • garnet material especially means and/or includes a material which comprises as a main constituent a material M ⁇ M ⁇ M ⁇ X-i ⁇ with M 1 selected out of the group Mg, Ca, Y, Na, Sr, Gd, La, Ce, Pr, Nd, Sm, Eu, Dy, Tb, Ho, Er, Tm, Yb, Lu or mixtures thereof, M n selected out of the group Al, Ga, Mg, Zn, Y, Ge, Sc, Zr, Ti, Hf or mixtures thereof, M in selected out of the group Al, Si, B, Ge, Ga, V, As, Zn or mixtures thereof, X selected out of the group O, S, N, F, CI, Br, I, OH and mixtures thereof and built of M n X 6 octahedra and M in X 4 tetrahedra in which each octa
  • each tetrahedron shares its vertices with four octahedra, so that the composition of the framework is (M n X3)2(M in X2)3.
  • Larger ions M 1 occupy positions of 8-coordination (dodecahedral) in the interstices of the framework, giving the final composition or M I 3M n 2 (M III X 4 )3.
  • the at least one Ce(III) doped phosphor essentially is a garnet material.
  • additives may also be present in the bulk compositions. These additives particularly include such species known to the art as fluxes. Suitable fluxes include alkaline earth - or alkaline - metal oxides, borates, phosphates and halides such as fluorides, ammonium chloride, Si0 2 and the like and mixtures thereof.
  • the at least one Eu (II) doped phosphor comprises, preferably essentially is a SiAlON material.
  • the phosphor composition furthermore comprises an orange to red emitting phosphor material having a peak emission > 600 nm and ⁇ 650 nm, preferably > 608 nm and ⁇ 640 nm and most preferred > 610 nm and ⁇ 630 nm. It has shown for many applications within the present invention that this leads to white light with a decreased correlated color temperature variation for a wide range of blue LEDs emitting at different wavelength, which is advantageous for many actual applications and/or uses of the present invention.
  • said orange to red emitting phosphor material preferably comprises - more preferably essentially is - a Eu(II) and/or Mn(IV) doped phosphor emitting in the red spectral range (peak emission > 580 nm).
  • the invention can be applied for a large range of correlated color temperatures with 1500K ⁇ CCT ⁇ 10000K.
  • said orange to red emitting phosphor material preferably comprises - more preferably essentially is - a material chosen out of the group comprising (Bai_ x _y_ z Sr x Ca y Eu z ) 2 Si5-a-bAl a N8-a- 4 bO a + 4 b with 0 ⁇ x ⁇ l, 0 ⁇ y ⁇ 0.75, 0.005 ⁇ z ⁇ 0.08, 0 ⁇ a ⁇ 0.2 and 0 ⁇ b ⁇ 0.2 (especially preferred (Bao. 4 Sro. 6 )i. 6Si 4 .95N7.80o.
  • the phosphor composition can be provided in powder form, e.g. contained in a silicon layer. It should be noted that the (at least) two phosphors which make up the inventive phosphor compositions may be provided as a mixture or there may be e.g. two layers, each containing essentially only one phosphor material.
  • the phosphor composition may be provided as a ceramic.
  • the present invention furthermore relates to a LED, preferably a pcLED comprising a phosphor composition according to the present invention. Moreover, it relates to a method of fabricating such LEDs on a wafer level scale.
  • the present invention furthermore relates to the use of the inventive phosphor composition for the reduction of binning in the manufacture of pcLEDs and/ or improvement of color stability in pcLEDs.
  • the present invention furthermore relates to a method of improving the color point stability in pcLEDs by using a inventive phosphor composition.
  • the present invention furthermore relates to a phosphor composition and/or a LED according to the present invention, being used in one or more of the following applications:
  • Fig. 1 shows an absorption spectrum of a Ce (III) doped phosphor according to Example I of the present invention
  • Fig. 2 shows an absorption spectrum of two Eu (II) doped phosphor according to Example I and II of the present invention
  • Fig. 3 shows an absorption spectrum of a silicon layer comprising an inventive phosphor composition
  • Fig. 4 shows an absorption spectrum of inventive phosphor compositions as well as a Ce (III) doped phosphor and a Eu(II) doped phosphor according to one embodiment of the present invention
  • Fig. 5 shows a diagram illustrating CIE 1976 color points of LEDs using an inventive phosphor composition according to a further embodiment of the present invention
  • Fig. 6 shows three emission spectra of LEDs using an inventive phosphor composition according to a further embodiment of the present invention
  • Fig. 7 shows resulting CIE 1976 color points for the LEDs of Fig. 6;
  • Fig. 8 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention
  • Fig. 9 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention.
  • Fig. 10 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention
  • Fig. 11 shows resulting CIE 1976 color points for phosphor converted LEDs using only the combination of one green phosphor with a read emitting phosphor compared to the embodiment of the present invention shown in figure 12;
  • Fig. 12 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention.
  • a further Eu-doped phosphor is Sr 0 .97Ga 2 S4:Euo.o3.
  • the absorption coefficient of Y2.9iAl 5 Oi2:Ceo.o9 is shown in Fig. 1, the absorption coefficient of (Sr 0 .9Ca 0 .i)o.96Si202N2:Euo.o4 (straight line) and BOSE (dotted line) is shown in Fig. 2.
  • a 100 ⁇ thick layer of silicone containing 16.2 vol% of a 67 vol% (Sr 0 .9Ca 0 .i)o.96Si202N2:Euo.o4 + 33 vol% Y2.9iAl 5 Oi2:Ceo.o9 mixture was prepared.
  • Fig 3 shows an absorption spectrum with a (desired) flat absorption curve in the blue spectral range (430 - 460 nm).
  • the increase of absorption of the Ce(III) doped garnet phosphor from 430 nm to 460 nm compensates the decrease of absorption of the Eu(II) phosphor leading to a wanted flattened absorption behavior of the mixture.
  • iAl 5 Oi2:Ceo.o mixture was prepared and attached to blue LED light sources with 440, 442 and 448 nm peak emission.
  • Fig 5 shows the CIE 1976 color points of the three LEDs and in comparison the color points of the pure constituents of the mixture. The v' variation of the mixture is greatly reduced compared the color points of the pure constituents of the mixture on top of the same LED light sources.
  • a silicone sheet of ⁇ 90 ⁇ thickness containing 16.2 vol% of a 67 vol% (Sr 0 .9Ca 0 .i)o.96Si202N2:Euo.o4 + 33 vol% Y2.9iAl 5 Oi2:Ceo.o9 mixture is attached to another silicone sheet of ⁇ 15 ⁇ thickness containing 16.2 vol% of a red light emitting
  • the stack is attached to various blue LED light sources (peak emission at 440, 442, and 448 nm) with the red light emitting sheet of the stack oriented to the LED emission surface.
  • Fig. 6 shows the three emission spectra of the LEDs; it clearly can be seen that - although the blue light varies - the overall emission spectra is nearly identical, i.e. no "binning" of the pcLEDs is necessary.
  • Fig. 7 shows the resulting CIE 1976 color points of the LEDs. All color points are located close to the center of the 3500 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
  • a silicone layer of ⁇ 56 ⁇ thickness was prepared containing 5.9 vol% (Sr 0 .9Ca 0 .i)o.96Si202N2:Euo.o4 + 5.9 vol% Y2.9iAl 5 Oi2:Ceo.o9 + 8.1 vol% red nitride phosphor (peak emission of about 620 nm) mixture and applied to blue emitting LEDs with peak emission ranging from 430 to 470 nm.
  • Fig. 8 shows the resulting CIE 1976 color points of the LEDs. All color points are located within the 3500 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
  • Fig. 9 shows the resulting CIE 1976 color points of the LEDs made with pure combination of a red nitride phosphor (peak emission of about 620 nm) with (i) a Celll (Y2. iAl 5 Oi2:Ceo.o ) [line curve] or (ii) a EuII phosphor ((Sr 0 .9Ca 0 .i)o. 6Si202N2:Euo.o4) [dashed curve] . Only for blue peak emission wavelengths centered to +/- 4nm around the centre 450nm wavelength, color points are located within the 3500 K ANSI C78.377.
  • Bao.98Sr 0 .98Si0 4 :Eu 2+ o.o4 (BOSE) + 4.3 vol% Y 2 .9iAl 5 Oi2:Ce 0 .o9 + 10.5 vol% red nitride phosphor (peak emission of about 620 nm) mixture was applied to blue emitting LEDs with peak emission ranging from 430 to 470 nm.
  • Fig. 10 shows the resulting CIE 1976 color points of the LEDs. All color points are located within the 2700 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
  • a silicone layer of ⁇ 260 ⁇ thickness was prepared containing 4.4 vol% Sr 4 . 9 Al 5 Si2i02N35:Euo.i + 3.4 vol% Lu2.88Al 5 Oi2:Ceo.i2 + 12.3 vol% red nitride phosphor (peak emission of about 609 nm) mixture and applied to blue emitting LEDs with peak emission ranging from 430 to 470 nm.
  • Fig. 12 shows the resulting CIE 1976 color points of the LEDs. All color points are located within the 2700 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
  • Fig. 11 shows the resulting CIE 1976 color points of the LEDs made with pure combination of a red nitride phosphor (peak emission of about 609 nm) with (i) a Ce(III) Lu2.88Al 5 Oi2:Ceo.i2 [dashed curve] or (ii) a Eu(II) phosphor (Sr 4 . 9 Al 5 Si2i02N35:Euo.i) [line curve].
  • the invention provides a method of fabricating phosphor coated LEDs on a wafer level scale. The method comprises the step of providing a growth wafer or substrate on which a plurality of LEDs is fabricated.
  • the LEDs may be epitaxially grown on the growth wafer or may have been bonded to a host substrate.
  • the wafer can be made of many materials such as sapphire, silicon carbide, aluminium nitride, and gallium nitride.
  • the LEDs may be fabricated from different material systems, with a preferred material system being Group-Ill nitride based.
  • Group-Ill nitrides refer to those semiconductor compounds formed between nitrogen and elements in the Group III of the periodic table, usually aluminum, gallium and indium.
  • the term also refers to ternary and quaternary compounds, such as AlGaN and AlInGaN.
  • the layers of the LEDs generally comprise an active layer/region sandwiched between first and second oppositely doped epitaxial layers, all of which are formed successively on the growth wafer.
  • the active region is arranged to emit light with a wavelength in the range 430 - 470 nm.
  • the LED layers can initially be formed as continuous layers across the growth wafer or substrate. Subsequently, the layers may be partitioned or separated into individual LEDs, for instance by etching down to the wafer through the active region and doped layers, thus forming open areas between the LEDs. Alternatively, the active region and doped layers can remain continuous layers on the wafer and can be separated into individual devices when the (phosphor coated) LED chips are singulated.
  • the method further comprises the step of providing a wavelength conversion material.
  • the wavelength conversion material comprises the phosphor composition according to the first aspect of the invention.
  • the wavelength conversion material is mounted over the plurality of LEDs on the wafer.
  • the wavelength conversion material comprises a phosphor/binder coating that covers each of the plurality of LEDs on the wafer.
  • the phosphor/binder coating can be applied using different known processes, such as dispensing, jet printing, screen printing, electrophoretic deposition, or electrostatic deposition.
  • the wavelength conversion material can be fabricated as a separate preform that can be bonded to or mounted over the LEDs on the wafer.
  • the pre-form may for instance be a sheet of a transparent matrix material, such as silicone, in which the phosphor is dispersed.
  • the pre-form may be a stack of such sheets as for instance described in Example III above.
  • the pre-form may be a ceramic slab comprising the phosphor composition.
  • Such a wafer scale slab may be glued to the LEDs on the wafer, or may be bonded to the substrate (f.i. a sapphire host substrate) onto which LEDs have been transferred from the growth wafer.
  • the method further comprises the step of singulating the individual LED chips from the wafer. This can be realized using known methods such as dicing, scribe and breaking, or etching. The singulating process separates each of the (phosphor coated) LED chips with each having substantially the same emission characteristics. This allows for a reliable and consistent fabrication of LED chips having substantially similar emission characteristics.
  • the singulated phosphor coated LED chips may be packaged. This can comprise mounting the LED chips in a package, to a submount, or to printed circuit board. This can be done without the need for further processing to add or remove phosphor in order to achieve a consistent color point.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Luminescent Compositions (AREA)
  • Led Device Packages (AREA)

Abstract

The invention relates to a phosphor composition for LEDs with flat absorption curve in the blue spectral range (430 - 460 nm) by having a Ce (III) doped phosphor and a Eu (II) doped phosphor. The increase of absorption of the Ce(III) doped phosphor from 430 nm to 460 nm compensates the decrease of absorption of the Eu(II) phosphor leading to a wanted flattened absorption behavior of the mixture.

Description

Phosphor composition for LEDs
FIELD OF THE INVENTION
The present invention relates to the field of light emission diodes (LED). Particularly the invention relates to enhanced uniform emission phosphor-converting LED light assemblies (pcLED) and efficient manufacturing of the same.
BACKGROUND OF THE INVENTION
Process related variations in blue pump wavelengths lead to a certain color distribution in phosphor converted LED lamps and thus may reduce the overall production yield caused by pcLEDs showing unwanted color points (so called "binning").
Although several solutions to this problem have been proposed in the art (e.g. in the US20060057753, there is still the continuing need for alternative approaches which are able to at least partly overcome the binning problem especially for applications on a waver level scale. SUMMARY OF THE INVENTION
It is an object of the present invention to provide a phosphor composition for LEDs by which the binning can at least be partly overcome, especially for applications on a waver level scale.
This object is solved by phosphor composition according to claim 1 of the present invention. Accordingly, a phosphor composition for a LED is provided comprising at least one Ce (III) doped phosphor and at least one Eu (II) doped phosphor whereby
the Ce(III) doped phosphor has a lowest lying 4f→ 5d absorption band that peaks in the range > 440 to < 480 nm and has a spectral width (FWHM, full width at half maximum) in the range of > 2000 to < 4300 cm"1,
- whereby the Ce(III) doped phosphor has an emission band peaking in the range > 510 to < 570 nm
whereby the Eu (II) doped phosphor has an emission band peaking in the range > 490 to < 570 nm; and whereby at least one absorption coefficient k in the range of 420 to 450 nm of the Eu(II) doped phosphor is 50% of the absorption coefficient k' at 380 nm. The absorption coefficient k is known as the complex part of the index of refraction and usually is wavelength dependent. It relates to the absorption index a in the Beer-Lambert law according to a = 4π λ.. It should be noted that k and k' both refer to the same Eu(II) doped phosphor.
Such a phosphor composition has shown for a wide range of applications within the present invention to have at least one of the following advantages:
Using the inventive phosphor composition, LEDs can be manufactured, showing an extremely stable color point (usually a white color point, but this is not limiting: the invention can be used with LEDs to form other colors points as well) that is only slightly shifted by variations of the blue pump emission wavelength and thus shows significantly higher temperature and drive stability in combination with increased production yields.
Using the inventive phosphor composition, the LED color point also becomes a lot more stable as a function of temperature and drive current of the LED.
The use of the inventive phosphors is especially advantageous for applications which are designed for wafer level LED manufacturing where blue binning needs to be skipped.
The invention can be applied using conventional manufacturing techniques and avoiding sophisticated layouts of the production process.
Using the inventive phosphor composition, a complete wafer of LEDs with typically a (blue) peak emission in the range of 430 to 470 nm (due to variations in the processing at an epitaxial level) can be manufactured with a single thickness of the phosphor layer, showing an extremely stable color point within a 7-step McAdam ellipses lying within one nominal CCT Category, as defined by ANSI NEMA ANSLG C78.377-2008 American National Standard for Electric Lamps— Specifications for the Chromaticity of Solid State Lighting Products.
According to a preferred embodiment of the invention, the Ce(III) doped phosphor has a lowest lying 4f→ 5d absorption band which has a spectral width (FWHM, full width at half maximum) in the range of > 2400 to < 4000 cm"1.
According to a preferred embodiment of the invention, the sum of the absorption coefficients of said lowest lying 4f→ 5d absorption bands of (i) the Eu(II) doped phosphor and (ii) the Ce(III) doped phosphor has a minimum in the range > 380 to < 450 nm.
According to a preferred embodiment of the invention, the Ce(III) doped phosphor has a smaller CIE 1931 y color coordinate and/or a smaller x color coordinate than the Eu(II) doped phosphor. Preferably the difference in y color coordinate is > 0.01, preferably > 0.05 and most preferred > 0.07. Preferably the difference in x color coordinate is > 0.02, preferably > 0.08 and most preferred > 0.13.
According to a preferred embodiment of the invention, the Eu (II) doped phosphor has a lowest lying 4f→5d absorption band in the spectral range > 300 to < 520, preferably 460, more preferred < 430 nm.
According to a preferred embodiment of the invention, the lowest lying absorption band maximum of the Eu(II) doped phosphor is located at higher energies compared to the lowest lying absorption band maximum of the Ce(III) doped phosphor.
According to a preferred embodiment of the invention, the at least one Ce(III) doped phosphor comprises a garnet material. The term "garnet material" especially means and/or includes a material which comprises as a main constituent a material M^M^M^X-i^ with M1 selected out of the group Mg, Ca, Y, Na, Sr, Gd, La, Ce, Pr, Nd, Sm, Eu, Dy, Tb, Ho, Er, Tm, Yb, Lu or mixtures thereof, Mn selected out of the group Al, Ga, Mg, Zn, Y, Ge, Sc, Zr, Ti, Hf or mixtures thereof, Min selected out of the group Al, Si, B, Ge, Ga, V, As, Zn or mixtures thereof, X selected out of the group O, S, N, F, CI, Br, I, OH and mixtures thereof and built of MnX6 octahedra and MinX4 tetrahedra in which each octahedron is joint to six others through vertex-sharing tetrahedra. Each tetrahedron shares its vertices with four octahedra, so that the composition of the framework is (MnX3)2(MinX2)3. Larger ions M1 occupy positions of 8-coordination (dodecahedral) in the interstices of the framework, giving the final composition
Figure imgf000005_0001
or MI3Mn 2(MIIIX4)3.
These materials have proven themselves in practice since in most applications they fulfill the criteria for a phosphor according to the present invention. According to a preferred embodiment of the invention, the at least one Ce(III) doped phosphor essentially is a garnet material.
The term "essentially" means especially > 95 %, preferably > 97 % and most preferred > 99 % wt-%. However, in some applications, trace amounts of additives may also be present in the bulk compositions. These additives particularly include such species known to the art as fluxes. Suitable fluxes include alkaline earth - or alkaline - metal oxides, borates, phosphates and halides such as fluorides, ammonium chloride, Si02 and the like and mixtures thereof.
According to a preferred embodiment of the invention, the at least one Ce(III) doped phosphor comprises, preferably essentially is a material with the following structure M3-xAl5_yGayOi2:Cex (M = Y, Lu, Gd), 0 < x < 1, 0 < y < 0.5. According to a preferred embodiment of the invention, the at least one Eu (II) doped phosphor comprises, preferably essentially is a SiAlON material.
According to a preferred embodiment of the invention, the at least one Eu (II) doped phosphor comprises, preferably essentially is a material chosen out of the group comprising Sri_xMx Si202N2:Eu (M = Ca, Ba) with 0 < x < 0.25 , M2Si04:Eu (M = Sr, Ca, Ba), M3Si60i2N2:Eu (M = Ba, Sr, Ca) or Sr5_y_z_aMySi23_xAl3+xOx+2aN37-x-2a:Euz with M = Ca, Ba; 0 < x < 7, 0 < y < 5, 0.0001 < z < 0.5, and 0 < a < 1.5, SrGa2S4:Eu, S
2xAlz+2xOzN8-z:Eux 0.005 < x < 0.04, 0.1 < z < 0.5 or mixtures thereof.
According to a preferred embodiment of the invention the phosphor composition furthermore comprises an orange to red emitting phosphor material having a peak emission > 600 nm and < 650 nm, preferably > 608 nm and < 640 nm and most preferred > 610 nm and < 630 nm. It has shown for many applications within the present invention that this leads to white light with a decreased correlated color temperature variation for a wide range of blue LEDs emitting at different wavelength, which is advantageous for many actual applications and/or uses of the present invention.
Preferably said orange to red emitting phosphor material preferably comprises - more preferably essentially is - a Eu(II) and/or Mn(IV) doped phosphor emitting in the red spectral range (peak emission > 580 nm). In this way the invention can be applied for a large range of correlated color temperatures with 1500K < CCT < 10000K.
In a more particulate preferred embodiment of the present invention, said orange to red emitting phosphor material preferably comprises - more preferably essentially is - a material chosen out of the group comprising (Bai_x_y_zSrxCayEuz)2Si5-a-bAlaN8-a-4bOa+4b with 0 < x < l, 0 < y < 0.75, 0.005 < z < 0.08, 0 < a < 0.2 and 0 < b < 0.2 (especially preferred (Bao.4Sro.6)i. 6Si4.95N7.80o.2 :Eu0.o4), Mi_x_y_zSii+x_zAli_x+zN3_xOx:Euy,Cez with M = Ca, Sr, Ba, Mg, 0 < x < 0.05, 0.002 < y < 0.05, 0 < z < 0.08 (especially preferred
(Cao.5Sro.5)o. 75Sii.oi5Alo.985N2.9850o.oi5:Euo.oi), Mi_xSi_ySey:Eux, with M = Ca, Sr, Mg
(especially preferred Cao.9995So.2Seo.8:Euo.ooos), A2Sii_xF6:Mnx with A = K, Na, Li, Rb
(especially preferred K2Sio.95F6:Mno.o5) or mixtures thereof.
The phosphor composition can be provided in powder form, e.g. contained in a silicon layer. It should be noted that the (at least) two phosphors which make up the inventive phosphor compositions may be provided as a mixture or there may be e.g. two layers, each containing essentially only one phosphor material.
Alternatively the phosphor composition may be provided as a ceramic. The present invention furthermore relates to a LED, preferably a pcLED comprising a phosphor composition according to the present invention. Moreover, it relates to a method of fabricating such LEDs on a wafer level scale.
The present invention furthermore relates to the use of the inventive phosphor composition for the reduction of binning in the manufacture of pcLEDs and/ or improvement of color stability in pcLEDs.
The present invention furthermore relates to a method of improving the color point stability in pcLEDs by using a inventive phosphor composition.
The present invention furthermore relates to a phosphor composition and/or a LED according to the present invention, being used in one or more of the following applications:
office lighting systems
household application systems
shop lighting systems,
home lighting systems,
accent lighting systems,
spot lighting systems,
theater lighting systems,
fiber-optics application systems,
projection systems,
self-lit display systems,
pixilated display systems,
segmented display systems,
warning sign systems,
medical lighting application systems,
indicator sign systems, and
decorative lighting systems
portable systems
automotive applications
green house lighting systems
The aforementioned components, as well as the claimed components and the components to be used in accordance with the invention in the described embodiments, are not subject to any special exceptions with respect to their size, shape, material selection and technical concept such that the selection criteria known in the pertinent field can be applied without limitations.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional details, features, characteristics and advantages of the object of the invention are disclosed in the sub-claims, the figures and the following description of the respective figures and examples, which— in an exemplary fashion— show several embodiments and examples of inventive phosphor compositions according to the invention.
Fig. 1 shows an absorption spectrum of a Ce (III) doped phosphor according to Example I of the present invention;
Fig. 2 shows an absorption spectrum of two Eu (II) doped phosphor according to Example I and II of the present invention;
Fig. 3 shows an absorption spectrum of a silicon layer comprising an inventive phosphor composition;
Fig. 4 shows an absorption spectrum of inventive phosphor compositions as well as a Ce (III) doped phosphor and a Eu(II) doped phosphor according to one embodiment of the present invention;
Fig. 5 shows a diagram illustrating CIE 1976 color points of LEDs using an inventive phosphor composition according to a further embodiment of the present invention;
Fig. 6 shows three emission spectra of LEDs using an inventive phosphor composition according to a further embodiment of the present invention;
Fig. 7 shows resulting CIE 1976 color points for the LEDs of Fig. 6;
Fig. 8 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention;
Fig. 9 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention;
Fig. 10 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention;
Fig. 11 shows resulting CIE 1976 color points for phosphor converted LEDs using only the combination of one green phosphor with a read emitting phosphor compared to the embodiment of the present invention shown in figure 12;
Fig. 12 shows resulting CIE 1976 color points for phosphor converted LEDs according to a further embodiment of the present invention. EXAMPLES
The invention will further be understood by the following Examples which merely for illustration and which is non-binding.
In the following Examples the listed phosphor materials are used, whose spectral data is given in Table I and Table II below:
TABLE I : Ce-doped phosphors
Figure imgf000009_0001
TABLE II : Eu-doped phosphors
Figure imgf000009_0002
A further Eu-doped phosphor is Sr0.97Ga2S4:Euo.o3.
The absorption coefficient of Y2.9iAl5Oi2:Ceo.o9 is shown in Fig. 1, the absorption coefficient of (Sr0.9Ca0.i)o.96Si202N2:Euo.o4 (straight line) and BOSE (dotted line) is shown in Fig. 2.
EXAMPLE I
In a first Example, a 100 μιη thick layer of silicone containing 16.2 vol% of a 67 vol% (Sr0.9Ca0.i)o.96Si202N2:Euo.o4 + 33 vol% Y2.9iAl5Oi2:Ceo.o9 mixture was prepared. Fig 3 shows an absorption spectrum with a (desired) flat absorption curve in the blue spectral range (430 - 460 nm). The increase of absorption of the Ce(III) doped garnet phosphor from 430 nm to 460 nm compensates the decrease of absorption of the Eu(II) phosphor leading to a wanted flattened absorption behavior of the mixture.
In order to illustrate the compensation, a more detailed curve is shown in Fig. 4.
EXAMPLE II
In a second example, a 90 μιη thick layer of silicone containing 20 vol% of a 60 vol% (Sr0.9Ca0.i)o. 6Si202N2:Euo.o4 + 40 vol% Y2. iAl5Oi2:Ceo.o mixture was prepared and attached to blue LED light sources with 440, 442 and 448 nm peak emission. Fig 5 shows the CIE 1976 color points of the three LEDs and in comparison the color points of the pure constituents of the mixture. The v' variation of the mixture is greatly reduced compared the color points of the pure constituents of the mixture on top of the same LED light sources. EXAMPLE III
A silicone sheet of ~ 90 μιη thickness containing 16.2 vol% of a 67 vol% (Sr0.9Ca0.i)o.96Si202N2:Euo.o4 + 33 vol% Y2.9iAl5Oi2:Ceo.o9 mixture is attached to another silicone sheet of ~ 15 μιη thickness containing 16.2 vol% of a red light emitting
(BaSr)i.96Si5N8:Euo.o4 powder. The stack is attached to various blue LED light sources (peak emission at 440, 442, and 448 nm) with the red light emitting sheet of the stack oriented to the LED emission surface.
Fig. 6 shows the three emission spectra of the LEDs; it clearly can be seen that - although the blue light varies - the overall emission spectra is nearly identical, i.e. no "binning" of the pcLEDs is necessary.
Fig. 7 shows the resulting CIE 1976 color points of the LEDs. All color points are located close to the center of the 3500 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations. EXAMPLE IV
A silicone layer of ~ 56 μιη thickness was prepared containing 5.9 vol% (Sr0.9Ca0.i)o.96Si202N2:Euo.o4 + 5.9 vol% Y2.9iAl5Oi2:Ceo.o9 + 8.1 vol% red nitride phosphor (peak emission of about 620 nm) mixture and applied to blue emitting LEDs with peak emission ranging from 430 to 470 nm. Fig. 8 shows the resulting CIE 1976 color points of the LEDs. All color points are located within the 3500 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
In contrast to the above embodiment, Fig. 9 shows the resulting CIE 1976 color points of the LEDs made with pure combination of a red nitride phosphor (peak emission of about 620 nm) with (i) a Celll (Y2. iAl5Oi2:Ceo.o ) [line curve] or (ii) a EuII phosphor ((Sr0.9Ca0.i)o. 6Si202N2:Euo.o4) [dashed curve] . Only for blue peak emission wavelengths centered to +/- 4nm around the centre 450nm wavelength, color points are located within the 3500 K ANSI C78.377.
EXAMPLE V
A silicone layer of - 140 μιη thickness containing 5.2 vol%
Bao.98Sr0.98Si04:Eu2+o.o4 (BOSE) + 4.3 vol% Y2.9iAl5Oi2:Ce0.o9 + 10.5 vol% red nitride phosphor (peak emission of about 620 nm) mixture was applied to blue emitting LEDs with peak emission ranging from 430 to 470 nm.
Fig. 10 shows the resulting CIE 1976 color points of the LEDs. All color points are located within the 2700 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
EXAMPLE VI
A silicone layer of ~ 260 μιη thickness was prepared containing 4.4 vol% Sr4.9Al5Si2i02N35:Euo.i + 3.4 vol% Lu2.88Al5Oi2:Ceo.i2 + 12.3 vol% red nitride phosphor (peak emission of about 609 nm) mixture and applied to blue emitting LEDs with peak emission ranging from 430 to 470 nm.
Fig. 12 shows the resulting CIE 1976 color points of the LEDs. All color points are located within the 2700 K ANSI C78.377 A color bin, thus the influence of blue pump bin variations are greatly reduced compared to binary green/yellow + red phosphor combinations.
In contrast to the above embodiment, Fig. 11 shows the resulting CIE 1976 color points of the LEDs made with pure combination of a red nitride phosphor (peak emission of about 609 nm) with (i) a Ce(III) Lu2.88Al5Oi2:Ceo.i2 [dashed curve] or (ii) a Eu(II) phosphor (Sr4.9Al5Si2i02N35:Euo.i) [line curve]. According to another aspect the invention provides a method of fabricating phosphor coated LEDs on a wafer level scale. The method comprises the step of providing a growth wafer or substrate on which a plurality of LEDs is fabricated. For instance the LEDs may be epitaxially grown on the growth wafer or may have been bonded to a host substrate. The wafer can be made of many materials such as sapphire, silicon carbide, aluminium nitride, and gallium nitride. The LEDs may be fabricated from different material systems, with a preferred material system being Group-Ill nitride based. Group-Ill nitrides refer to those semiconductor compounds formed between nitrogen and elements in the Group III of the periodic table, usually aluminum, gallium and indium. The term also refers to ternary and quaternary compounds, such as AlGaN and AlInGaN. The layers of the LEDs generally comprise an active layer/region sandwiched between first and second oppositely doped epitaxial layers, all of which are formed successively on the growth wafer. Preferably, the active region is arranged to emit light with a wavelength in the range 430 - 470 nm. The LED layers can initially be formed as continuous layers across the growth wafer or substrate. Subsequently, the layers may be partitioned or separated into individual LEDs, for instance by etching down to the wafer through the active region and doped layers, thus forming open areas between the LEDs. Alternatively, the active region and doped layers can remain continuous layers on the wafer and can be separated into individual devices when the (phosphor coated) LED chips are singulated.
The method further comprises the step of providing a wavelength conversion material. The wavelength conversion material comprises the phosphor composition according to the first aspect of the invention. The wavelength conversion material is mounted over the plurality of LEDs on the wafer. In one embodiment, the wavelength conversion material comprises a phosphor/binder coating that covers each of the plurality of LEDs on the wafer. The phosphor/binder coating can be applied using different known processes, such as dispensing, jet printing, screen printing, electrophoretic deposition, or electrostatic deposition. Alternatively, the wavelength conversion material can be fabricated as a separate preform that can be bonded to or mounted over the LEDs on the wafer. The pre-form may for instance be a sheet of a transparent matrix material, such as silicone, in which the phosphor is dispersed. Alternatively, the pre-form may be a stack of such sheets as for instance described in Example III above. Alternatively still, the pre-form may be a ceramic slab comprising the phosphor composition. Such a wafer scale slab may be glued to the LEDs on the wafer, or may be bonded to the substrate (f.i. a sapphire host substrate) onto which LEDs have been transferred from the growth wafer. The method further comprises the step of singulating the individual LED chips from the wafer. This can be realized using known methods such as dicing, scribe and breaking, or etching. The singulating process separates each of the (phosphor coated) LED chips with each having substantially the same emission characteristics. This allows for a reliable and consistent fabrication of LED chips having substantially similar emission characteristics. Advantageously, with this fabrication method one avoids the need to measure the individual emission characteristics of the "naked" (i.e. non-phosphor coated) LED chips, generate a mapping of these characteristics over the wafer, and adjust the (f.i. amount or concentration) wavelength conversion material in accordance with the mapping to obtain a substantially single color point of all the LEDs on the wafer.
The singulated phosphor coated LED chips may be packaged. This can comprise mounting the LED chips in a package, to a submount, or to printed circuit board. This can be done without the need for further processing to add or remove phosphor in order to achieve a consistent color point.
It is understood that the method described above does not necessarily have to be applied to a full wafer. It can also be applied in processing less than a full wafer.
Alternatively, it can be applied in processing a group of LEDs separated as a group from the wafer.
The particular combinations of elements and features in the above detailed embodiments are exemplary only; the interchanging and substitution of these teachings with other teachings in this and the patents/applications incorporated by reference are also expressly contemplated. As those skilled in the art will recognize, variations, modifications, and other implementations of what is described herein can occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed.
Accordingly, the foregoing description is by way of example only and is not intended as limiting. 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 measured cannot be used to advantage. The invention's scope is defined in the following claims and the equivalents thereto. Furthermore, reference signs used in the description and claims do not limit the scope of the invention as claimed.

Claims

CLAIMS:
1. A phosphor composition for a LED is comprising at least one Ce (III) doped phosphor and at least one Eu (II) doped phosphor whereby
the Ce(III) doped phosphor has a lowest lying 4f→ 5d absorption band that peaks in the range > 440 to < 480 nm and has a spectral width (FWHM, full width at half maximum) in the range of > 2000 to < 4300 cm"1,
whereby the Ce(III) doped phosphor has an emission band peaking in the range > 510 to < 570 nm
whereby the Eu (II) doped phosphor has an emission band peaking in the range > 490 to < 570 nm
- and whereby at least one absorption coefficient k in the range of 420 to 450 nm of the Eu(II) doped phosphor is 50% of the absorption coefficient k' at 380 nm.
2. The phosphor composition according to claim 1, whereby the Ce(III) doped phosphor has a lowest lying 4f→ 5d absorption band which has a spectral width (FWHM, full width at half maximum) in the range of > 2400 to < 4000 cm"1.
3. The phosphor composition according to claim 1 or 2, whereby the sum of the absorption coefficient of said lowest lying 4f→ 5d absorption bands of the Eu(II) doped phosphor and of the Ce(III) doped phosphor has a minimum in the range > 380 to < 450 nm.
4. The phosphor composition according to any of the claims 1 to 3, whereby the Eu (II) doped phosphor has a lowest lying 4f→5d absorption band in the spectral range > 370 to < 460 nm.
5. The phosphor composition according to any of the claims 1 to 4, whereby the
Ce(III) doped phosphor comprises a garnet material.
6. The phosphor composition according to any of the claims 1 to 5, whereby the at least one Eu (II) doped phosphor comprises a SiAlON-material.
7. The phosphor composition according to any of the claims 1 to 6, whereby the at least one Ce(III) doped phosphor comprises a material with the following structure M3_ xAl5_yGayOi2:Cex (M = Y, Lu, Gd).
8. The phosphor composition according to any of the claims 1 to 7 whereby the Eu (II) doped phosphor comprises a material chosen out of the group comprising Sri_xMx Si202N2:Eu (M = Ca, Ba) with 0 < x < 0.25 , M2Si04:Eu (M = Sr, Ca, Ba), M3Si60i2N2:Eu (M = Ba, Sr, Ca) or Sr5_y_z_aMySi23_xAl3+xOx+2aN37-x-2a:Euz with M = Ca, Ba; 0 < x < 7, 0 < y < 5, 0.0001 < z < 0.5, and 0 < a < 1.5, SrGa2S4:Eu, Si6-z-2xAlz+2xOzN8-z:Eux 0.005 < x < 0.04, 0.1 < z < 0.5 or mixtures thereof.
9. Use of a phosphor composition according to any of the claims 1 to 8 for the reduction of binning in the manufacture of pcLEDs and/or improvement of the color stability in pcLEDs.
10. A system comprising a phosphor composition according to any of the claims 1 to 8, the system being used in one or more of the following applications:
office lighting systems
household application systems
shop lighting systems,
home lighting systems,
accent lighting systems,
spot lighting systems,
theater lighting systems,
fiber-optics application systems,
projection systems,
self-lit display systems,
pixilated display systems,
segmented display systems,
warning sign systems,
medical lighting application systems,
indicator sign systems, and
decorative lighting systems portable systems
automotive applications
green house lighting systems
11. A method for fabricating phosphor coated LEDs on a wafer level scale, the method comprising:
providing a wafer on which a plurality of LEDs are fabricated;
providing a wavelength conversion material comprising the phosphor composition according to any of the claims 1 to 8;
mounting the wavelength conversion material over the wafer for forming phosphor coated LEDs;
singulating individual phosphor coated LEDs from the wafer.
12. A method of improving the color point stability in pcLEDs by using a phosphor composition according to any of the claims 1 to 8.
PCT/IB2012/051018 2011-03-10 2012-03-05 Phosphor composition for leds WO2012120433A1 (en)

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