WO2010041195A1 - Blue emitting sion phosphor - Google Patents

Blue emitting sion phosphor Download PDF

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Publication number
WO2010041195A1
WO2010041195A1 PCT/IB2009/054361 IB2009054361W WO2010041195A1 WO 2010041195 A1 WO2010041195 A1 WO 2010041195A1 IB 2009054361 W IB2009054361 W IB 2009054361W WO 2010041195 A1 WO2010041195 A1 WO 2010041195A1
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Prior art keywords
light emitting
emitting device
phosphor
systems
material according
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PCT/IB2009/054361
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French (fr)
Inventor
Andreas Tuecks
Peter J. Schmidt
Hans-Helmut Bechtel
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Philips Intellectual Property & Standards Gmbh
Koninklijke Philips Electronics N. V.
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Publication of WO2010041195A1 publication Critical patent/WO2010041195A1/en

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    • H—ELECTRICITY
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    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B33/00—Electroluminescent light sources
    • H05B33/12—Light sources with substantially two-dimensional radiating surfaces
    • H05B33/14—Light sources with substantially two-dimensional radiating surfaces characterised by the chemical or physical composition or the arrangement of the electroluminescent material, or by the simultaneous addition of the electroluminescent material in or onto the light source
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    • 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
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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/597—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon oxynitride, e.g. SIALONS
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    • 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
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
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    • C04B2235/3205—Alkaline earth oxides or oxide forming salts thereof, e.g. beryllium oxide
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/54—Particle size related information
    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
    • C04B2235/5436—Particle size related information expressed by the size of the particles or aggregates thereof micrometer sized, i.e. from 1 to 100 micron
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/02—Composition of constituents of the starting material or of secondary phases of the final product
    • C04B2235/50—Constituents or additives of the starting mixture chosen for their shape or used because of their shape or their physical appearance
    • C04B2235/54—Particle size related information
    • C04B2235/5418—Particle size related information expressed by the size of the particles or aggregates thereof
    • C04B2235/5445—Particle size related information expressed by the size of the particles or aggregates thereof submicron sized, i.e. from 0,1 to 1 micron
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/74—Physical characteristics
    • C04B2235/77—Density
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
    • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
    • H01L2224/484—Connecting portions
    • H01L2224/48463—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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

Definitions

  • the present invention is directed to novel luminescent materials for light emitting devices, especially to the field of novel luminescent materials for LEDs.
  • pcLEDs white phosphor converted LEDs
  • 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, SiO 2 and the like and mixtures thereof. Such a material has shown for a wide range of applications within the present invention to have at least one of the following advantages:
  • the material shows for a wide range of applications a high chemical and thermal stability; - The material has a very narrow emission band resulting in a very high color purity;
  • the material has a small Stokes Shift
  • the quantum loss (loss by the conversion of the excitation light into blue photons emitted by the phosphor) can be kept low by properly choosing the wavelength of the excitation source; -
  • the material is exciteable with wavelengths of > 250 nm to ⁇ 470 nm, in particular of
  • the material is for a wide range of applications substantially non-hazardous
  • the material can be synthesized for a wide range of applications of widely available starting materials
  • the material can be used for a wide range of display applications, especially of very high color purity
  • the material can be used for a wide range of applications with any combination of UV - blue radiation sources with maximum wavelengths ⁇ 470 nm; -
  • the efficiency of a combination of the material and a pump LED with wavelengths of about > 420 nm to ⁇ 430 nm can for a wide range of applications be higher than the efficiency of a direct emitting blue LED that emits in the wavelength range of the material; LEDs may be built on the basis of the material, which show improved lighting features, especially excellent luminous efficiency, drive and temperature independent color rendition and color point;
  • the material can fill the so-called "cyan gap" in phosphor converted LEDs, using blue pump LEDs with peak wavelengths in the range of > 250 nm to ⁇ 470 nm, in particular of > 360 nm to ⁇ 460 nm, and thereby can increase the lumen output and color rendition of phosphor converted LEDs; and/or
  • the material can be produced by a low-cost production process, especially making it also attractive for remote phosphor applications where generally larger amounts of phosphor per lumen package are needed compared to phosphor-on-chip configurations. Without being bound to any theory, the inventors believe that the improved properties of the inventive material arise at least partially out of the structure of the material.
  • the material comprises Europium in its divalent oxidation state (Eu 2+ ).
  • x is 0.23 ⁇ x ⁇ 0.27, preferably > 0.24 and ⁇ 0.26. This has been found to be advantageous for a wide range of applications within the present invention.
  • the material can further comprise at least one codopant M, for example for enhancing crystallization and absorption properties.
  • the material can further comprise a codopant M selected from the group comprising rare earth metals, scandium, yttrium, lanthan, cerium, for example Ce 3+ , manganese, for example Mn 2+ , or mixtures thereof.
  • the doping level of Europium is > 0.1 mol-% to ⁇ 10 mol-%, with respect to the stochiometric sum of Barium, Strontium, Europium and the optional codopant/s M.
  • the doping level of Europium is > 0.5 mol-% to ⁇ 5 mol-%, and more preferred > 1 mol-% to ⁇ 3 mol-%, with respect to the stochiometric sum of Barium, Strontium, Europium and the optional codopant/s M.
  • the doping level of the codopant M can for example be > 0 mol-% to ⁇ 5 mol- %, with respect to the stochiometric sum of Barium, Strontium, Europium and codopant/s M.
  • the material can be (Bai_ x _ y _ z Sr x )Si 2 O 2 N 2 :Eu y ,M z , whereby M is selected from the group comprising rare earth metals, scandium, yttrium, lanthan, cerium, maganese or mixtures thereof, and 0.20 ⁇ x ⁇ 0.30; 0.001 ⁇ y ⁇ 0.1 and 0 ⁇ z ⁇ 0.05.
  • the material can be (Ba 0 .75Sr 0 . 2 3Euo.o 2 )Si 2 0 2 N 2 .
  • the material has a peak emission wavelength ⁇ max of > 460 nm to ⁇ 480 nm and/or a full width at half maximum FWHM of > 20 nm to ⁇ 60 nm, preferably of > 30 nm to ⁇ 50 nm.
  • the material is excitable with wavelengths of ⁇ 470 nm, for example of > 250 nm to ⁇ 470 nm, in particular of ⁇ 460 nm, for example of > 360 nm to ⁇ 460 nm.
  • the present invention furthermore relates to the use of the materials as described above as a luminescent material.
  • the present invention furthermore relates to a light emitting device, especially a LED, comprising at least one material as described above.
  • the material is thereby provided, in particular at least partially, as powder and/or as monolithic ceramic material.
  • monolithic ceramic material in the sense of the present invention means and/or includes especially a crystalline or polycrystalline compact material or composite material with a controlled amount of pores or which is pore free.
  • polycrystalline material in the sense of the present invention means and/or includes especially a material with a volume density larger than 90 percent of the main constituent, consisting of more than 80 percent of single crystal domains, with each domain being larger than 0.5 ⁇ m in diameter and having different crystallographic orientations.
  • the single crystal domains may be connected by amorphous or glassy material or by additional crystalline constituents.
  • the powder has a mean particle size of > 0.2 ⁇ m to ⁇ 100 ⁇ m, more preferably of > 1 ⁇ m to
  • the monolithic ceramic material has > 90 %, and in particular ⁇ 100 %, of its theoretical density. This has been shown to be advantageous for a wide range of applications within the present invention since then the luminescence and optical properties of the at least one ceramic material may be increased.
  • the monolithic ceramic material has a density of >97% and ⁇ 100% of the theoretical density, yet more preferred > 98 % and ⁇ 100 %, even more preferred > 98.5 % and ⁇ 100 % and most preferred > 99.0 % and ⁇ 100 %.
  • the light emitting device comprises a UV and/or blue radiation source with a peak wavelength
  • ⁇ 470 nm for example > 250 nm to ⁇ 470 nm, in particular ⁇ 460 nm, for example of > 360 nm to ⁇ 460 nm.
  • the material can thereby be provided on the radiation source, in particular a LED chip, as powder layer and/or as monolithic ceramic material layer.
  • the light emitting device is a white or blue phosphor converted LED, comprising the material and at least one additional phosphor.
  • the additional phosphor can thereby be provided on the material according to the invention, in particular on a layer of the material according to the invention, as powder layer and/or as monolithic ceramic material layer.
  • the light emitting device is a white phosphor converted LED, comprising the material, a yellow and/or green emitting phosphor, and a red emitting phosphor. This has been shown to be advantageous for a wide range of applications within the present invention since then in combination with a UV - blue emitting LED superior white light sources can be produced.
  • the yellow and/or green emitting phosphor can thereby for example be selected from the group comprising Ce(III) doped yttrium aluminum garnets (YAG:Ce), SrSi 2 O 2 N 2 IEu or mixtures thereof and/or the red emitting phosphor can be a nitride red phosphor such as (Ca,Sr)SiAlN3:Eu and/or (Ba,Sr,Ca) 2 SisN8:Eu.
  • the present invention furthermore relates to a material and/or a light emitting device that may be of use in a broad variety of systems and/or applications, amongst them one or more of the following:
  • Display systems for example pixelated and/or segmented display systems, 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, warning sign systems, medical lighting application systems, indicator sign systems, and decorative lighting systems portable systems - automotive applications green house lighting systems
  • Fig. 1 shows the emission, excitation and reflectance spectrum of
  • Fig. 2 shows a diagram of a thermal quenching test
  • FIG. 3 shows emission spectra of (Bao.75Sro. 2 3Euo.o 2 )Si 2 0 2 N 2 for different temperatures;
  • Fig. 4 shows the XRD powder pattern of (Bao.75Sro. 2 3Euo.o 2 )Si 2 0 2 N 2 ;
  • Fig. 5 shows the XRD powder pattern of the comparative example
  • Fig. 7 shows a schematic crosssectional view of a first embodiment of a light emitting device according to the invention;
  • Fig. 7 shows a schematic crosssectional view of a first embodiment of a light emitting device according to the invention
  • Fig. 8 shows a schematic crosssectional view of a second embodiment of a light emitting device according to the invention
  • Fig. 9 shows the emission spectrum of a blue LED with a YAG and a red nitride phosphor and the emission spectrum of (Bao.7 5 Sr 0 .23Euo.o2)Si2 ⁇ 2N2;
  • Fig. 10 shows the emission spectra of two light emitting devices comprising
  • Fig. 11 shows a scanning electron micrograph of (Bao.75Sro. 2 3Euo.o 2 )Si 2 ⁇ 2 N 2 phosphor particles.
  • Figs. 1 to 4 refer to (Ba 0 .75Sr 0 . 2 3Euo.o 2 )Si 2 ⁇ 2 N 2 which was made according to the following:
  • Blue emitting (Ba 0 .75Sr 0 .23Euo.o2)Si2 ⁇ 2N2 was synthesized by mixing crystalline sub-micron (Bao.7sSro. 2 3Euo.o 2 ) 2 Si0 4 and S13N 4 in a planetary ball-mill and firing the resulting mixture in reducing N 2 /H 2 (5 %) atmosphere at 1300 -1400 0 C in a molybdenum crucible. After grinding, the intermediate product was ref ⁇ red under the same reaction conditions. The raw product was finally ball-milled and screened with a 15 ⁇ m sieving gauze.
  • compositions of two separately synthesized samples have been found to be (Ba 0 .75Sr 0 .23Euo.o2)Si2.o ⁇ 2.oN2.o and (Bao.74Sro.24Euo.o2)Si2.o ⁇ 2.iN2.o, which is (within instrumental uncertainty) in excellent agreement with the chemical formula given above.
  • the precursor material synthesized as described above may be mixed with BaCl 2 and sintered in N 2 /H 2 (5 %) atmosphere. The resulting powder was washed to remove flux residues and dried.
  • Fig. 1 shows the emission 1, excitation 2 and reflectance 3 spectrum of (Bao.75Sro. 2 3Euo.o 2 )Si 2 ⁇ 2 N 2 phosphor powder.
  • the emission sprectrum 1 shows that
  • Fig. 3 shows emission spectra of (Ba 0 .75Sr 0 . 2 3Euo.o 2 )Si 2 ⁇ 2 N 2 phosphor powder taken with an excitation at 415 nm at different temperatures ranging from 25 0 C up to 330 0 C.
  • Reference signs 10, 11, 12, and 13 thereby indicate the data taken at 25 0 C, 125 0 C, 200 0 C, and 330 0 C, respectively. Except for a slight broadening ( ⁇ 54 nm at 330 0 C, 13) no additional shift or change of shape of the spectra can be observed.
  • Fig. 4 shows the XRD powder pattern of (Ba 0 .75Sr 0 . 2 3Euo.o 2 )Si 2 ⁇ 2 N 2 phosphor powder
  • Fig. 5 shows the XRD powder pattern of the comparative phosphor powder (Bao.98Euo.o 2 )Si 2 ⁇ 2 N 2 .
  • the X-ray diffraction patterns were thereby measured for powder samples with Cu-Ka radiation and with Bragg-Brentano measuring geometry.
  • Fig. 6 shows a series of emission spectra comprising the emission spectrum of (Bao.75Sro. 2 3Euo.o 2 )Si 2 ⁇ 2 N 2 1 and the comparative emission spectra of BaSi 2 O 2 N 2 :Eu 2+ 4, SrSi 2 O 2 N 2 IEu 2+ 5, (Bao. 5 Sro. 5 )Si 2 0 2 N 2 :Eu 2+ 6 and CaSi 2 O 2 N 2 :Eu 2+ 7.
  • Fig. 6 exhibits that
  • the light emitting device comprises a radiation source 21, for example a UV and/or blue radiation source with a peak wavelength ⁇ 470 nm, in particular ⁇ 460 nm, for example an InGaN LED emitting at > 380 nm to ⁇ 440 nm, and a material 22 according to the invention, for example (Bao.75Sro.23Euo.o2)Si2 ⁇ 2N2.
  • the radiation source 21 can be for example an LED chip on a submount with bond wires.
  • the material 22 according to the invention is provided on the radiation source 21, in particular the LED chip, as powder layer and/or as monolithic ceramic material layer.
  • the light emitting device according to this embodiment can emit blue light 23.
  • Fig. 8 shows a schematic crosssectional view of a second embodiment of a light emitting device, in particular a phosphor converted light emitting device (pcLED).
  • the light emitting device also comprises a radiation source 21, for example a UV and/or blue radiation source with a peak wavelength ⁇ 470 nm, in particular ⁇ 460 nm, for example an InGaN LED emitting at > 380 nm to ⁇ 440 nm, and a material 22 according to the invention, for example (Bao.75Sro.23Euo.o2)Si2 ⁇ 2N2.
  • the radiation source 21 can be for example an LED chip on a submount with bond wires.
  • the material 22 according to the invention is also provided on the radiation source 21, in particular the LED chip, as powder layer and/or as monolithic ceramic material layer.
  • the light emitting device comprises in this embodiment an additional phosphor 24, for example yellow emitting (Y,Gd) 3 AlsOi 2 :Ce (2 %).
  • the additional phosphor 24 is in this embodiment provided on the material 22 according to the invention, as powder layer and/or as monolithic ceramic material layer.
  • the light emitting device according to this embodiment can emit blue 23 and for example yellow 25 light.
  • Fig. 9 shows the emission spectrum of a blue LED emitting at a peak wavelength of 450 nm with a YAG and a red nitride phosphor (full line) 31 and the emission spectrum of (Bao.75Sro.23Euo.o2)Si2 ⁇ 2N2 (dashed line) 32.
  • Spectrum 31 shows the "cyan gap" at wavelength about 480 nm resulting from a gap between the emission of the blue LED and the yellow/green YAG:Ce phosphor.
  • Spectrum 32 shows that materials according to the invention, for example (Ba 0 .75Sr 0 .23Euo.o2)Si2 ⁇ 2N2, can be used to fill this cyan gap.
  • Fig. 10 shows the emission spectra of two light emitting devices comprising (Bao.75Sro.23Euo.o2)Si2 ⁇ 2N2 and one comparative light emitting device.
  • Line 33 (large dashes) thereby shows the emission spectrum of a (Bao.75Sro.
  • line 34 shows the emission spectrum of a (Ba 0 .75Sr 0 .23Euo.o2)Si2 ⁇ 2N2 blue phosphor, SrSi 2 O 2 N 2 :Eu green phosphor and a CaSiAlN 3 IEu nitride red phosphor.
  • Line 31 shows the emission spectrum of the comparative light emitting device with a blue LED emitting at a peak wavelength of 450 nm and with a YAG:Ce yellow/green phosphor and a CaSiAlN 3 :Eu red nitride phosphor
  • the (Ba 0 .75Sr 0 . 23 Euo.o2)Si 2 0 2 N 2 phosphor combines high white light quality, in particular high color rendering (Ra: color rendering) and lumen output (LE: lumen equivalent) and high color point stability at elevated temperatures. Additionally, (Bao.7sSro. 23 Euo.o2)Si 2 0 2 N 2 can show a high color point stability with increasing drive currents. Especially in combination with a green emitting SrSi 2 O 2 N 2 IEu phosphor, high-power white light sources with constant color points under demanding operating conditions can be generated.
  • high quality white light can be generated by using blue LEDs with peak wavelenghts of- 420 nm that are commonly more efficient than LEDs emitting in the 450 nm-470 nm range.
  • the excitation light of the short wavelength pump LED does not necessarily need to be fully converted into longer wavelength light by the phosphors as depicted in the spectra 33 and 34.
  • the pump wavelength for example in case of blue pump LEDs with wavelength of about 380 nm-450 nm, it might be advantageous to allow small amounts of leakage of the pump LED light since by this measure color rendition may further be enhanced.
  • Fig. 11 shows a scanning electron micrograph of (Ba 0 .75Sr 0 . 2 3Euo.o2)Si 2 0 2 N 2 phosphor grains.

Abstract

The invention relates to luminescent materials of the general formula:(Ba1- xSrx )Si2 O2 N2 :Eu with 0.20 <x <0.30 and its application in phosphor converted LEDs.

Description

BLUE EMITTING SION PHOSPHOR
FIELD OF THE INVENTION
The present invention is directed to novel luminescent materials for light emitting devices, especially to the field of novel luminescent materials for LEDs.
BACKGROUND OF THE INVENTION
As blue LEDs, in particular, have become practical in recent years, the development of white light sources utilizing such blue LEDs in combination with phosphor materials is being energetically pursued.
Especially SiON phosphor materials have been in the focus of interest and several materials have been proposed, for example in EP 1 571 194 Al. However, there is still the continuing need for narrow emitting luminescent materials, which are usable in a wide range of applications and especially allow the fabrication of white phosphor converted LEDs (pcLEDs) with optimized luminous efficiency and color rendering.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a material which is usable within a wide range of applications and especially allows the fabrication of white phosphor converted LEDs (pcLEDs) with optimized luminous efficiency and color rendering.
This object is solved by a material according to claim 1 of the present invention. Accordingly, an, in particular blue emitting, material (BaI-XSrx)Si2O2N2IEu with 0.20 < x < 0.30 is provided.
It should be noted that by the term ,,(Bai_xSrx)Si202N2:Eu" especially and/or additionally any material is meant and/or included, which has essentially this composition.
The term "essentially" means especially > 95 wt-%, preferably > 97 wt-% 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, SiO2 and the like and mixtures thereof. Such a material has shown for a wide range of applications within the present invention to have at least one of the following advantages:
The material shows for a wide range of applications a high chemical and thermal stability; - The material has a very narrow emission band resulting in a very high color purity;
The material has a small Stokes Shift;
Due to the small Stokes Shift, the quantum loss (loss by the conversion of the excitation light into blue photons emitted by the phosphor) can be kept low by properly choosing the wavelength of the excitation source; - The material is exciteable with wavelengths of > 250 nm to < 470 nm, in particular of
> 360 nm to < 460 nm, for example with highly efficient blue pump LEDs with
> 420 nm to < 440 nm emission wavelength;
The material is for a wide range of applications substantially non-hazardous;
The material can be synthesized for a wide range of applications of widely available starting materials;
The material can be used for a wide range of display applications, especially of very high color purity;
The material can be used for a wide range of applications with any combination of UV - blue radiation sources with maximum wavelengths < 470 nm; - The efficiency of a combination of the material and a pump LED with wavelengths of about > 420 nm to < 430 nm can for a wide range of applications be higher than the efficiency of a direct emitting blue LED that emits in the wavelength range of the material; LEDs may be built on the basis of the material, which show improved lighting features, especially excellent luminous efficiency, drive and temperature independent color rendition and color point;
The material can fill the so-called "cyan gap" in phosphor converted LEDs, using blue pump LEDs with peak wavelengths in the range of > 250 nm to < 470 nm, in particular of > 360 nm to < 460 nm, and thereby can increase the lumen output and color rendition of phosphor converted LEDs; and/or
The material can be produced by a low-cost production process, especially making it also attractive for remote phosphor applications where generally larger amounts of phosphor per lumen package are needed compared to phosphor-on-chip configurations. Without being bound to any theory, the inventors believe that the improved properties of the inventive material arise at least partially out of the structure of the material.
The inventors believe the material has an ordered distribution OfBa2+ and Sr2+ ions in the lattice. The inventors believe that this can take place within a layer of alkaline- earth metal ions, for example between the [Si2O2N2]2" layers, or in the formation of stacking variants, in which only Ba2+ or Sr2+ are located between subsequent [Si2O2N2]2" layers, whereas both is resulting in a superstructure.
DETAILED DESCRIPTION OF EMBODIMENTS
According to a preferred embodiment of the invention the material comprises Europium in its divalent oxidation state (Eu2+).
Within the scope of another preferred embodiment of the invention, x is 0.23 < x < 0.27, preferably > 0.24 and < 0.26. This has been found to be advantageous for a wide range of applications within the present invention.
The material can further comprise at least one codopant M, for example for enhancing crystallization and absorption properties. For example, the material can further comprise a codopant M selected from the group comprising rare earth metals, scandium, yttrium, lanthan, cerium, for example Ce3+, manganese, for example Mn2+, or mixtures thereof.
According to another preferred embodiment of the present invention, the doping level of Europium is > 0.1 mol-% to < 10 mol-%, with respect to the stochiometric sum of Barium, Strontium, Europium and the optional codopant/s M. This has been shown to lead to a material with improved lighting features for a wide range of application within the present invention. Preferably, the doping level of Europium is > 0.5 mol-% to < 5 mol-%, and more preferred > 1 mol-% to < 3 mol-%, with respect to the stochiometric sum of Barium, Strontium, Europium and the optional codopant/s M.
The doping level of the codopant M can for example be > 0 mol-% to < 5 mol- %, with respect to the stochiometric sum of Barium, Strontium, Europium and codopant/s M.
For example, the material can be (Bai_x_y_zSrx)Si2O2N2:Euy,Mz, whereby M is selected from the group comprising rare earth metals, scandium, yttrium, lanthan, cerium, maganese or mixtures thereof, and 0.20 < x < 0.30; 0.001 < y < 0.1 and 0 < z < 0.05. In particular the material can be (Ba0.75Sr0.23Euo.o2)Si202N2.
Within the scope of a preferred embodiment of the invention, the material has a peak emission wavelength λmax of > 460 nm to < 480 nm and/or a full width at half maximum FWHM of > 20 nm to < 60 nm, preferably of > 30 nm to < 50 nm. Within the scope of another preferred embodiment of the invention, the material is excitable with wavelengths of < 470 nm, for example of > 250 nm to < 470 nm, in particular of < 460 nm, for example of > 360 nm to < 460 nm.
The present invention furthermore relates to the use of the materials as described above as a luminescent material.
The present invention furthermore relates to a light emitting device, especially a LED, comprising at least one material as described above.
Preferably, the material is thereby provided, in particular at least partially, as powder and/or as monolithic ceramic material. The term "monolithic ceramic material" in the sense of the present invention means and/or includes especially a crystalline or polycrystalline compact material or composite material with a controlled amount of pores or which is pore free.
The term "polycrystalline material" in the sense of the present invention means and/or includes especially a material with a volume density larger than 90 percent of the main constituent, consisting of more than 80 percent of single crystal domains, with each domain being larger than 0.5 μm in diameter and having different crystallographic orientations. The single crystal domains may be connected by amorphous or glassy material or by additional crystalline constituents.
According to another preferred embodiment of the present invention, the powder has a mean particle size of > 0.2 μm to < 100 μm, more preferably of > 1 μm to
< 20 μm, and most preferably of > 3 μm to < 12 μm. This has been shown to be advantageous for a wide range of applications within the present invention.
Within the scope of another preferred embodiment of the present invention, the monolithic ceramic material has > 90 %, and in particular < 100 %, of its theoretical density. This has been shown to be advantageous for a wide range of applications within the present invention since then the luminescence and optical properties of the at least one ceramic material may be increased.
More preferably, the monolithic ceramic material has a density of >97% and < 100% of the theoretical density, yet more preferred > 98 % and < 100 %, even more preferred > 98.5 % and < 100 % and most preferred > 99.0 % and < 100 %.
According to another preferred embodiment of the present invention, the light emitting device comprises a UV and/or blue radiation source with a peak wavelength
< 470 nm, for example > 250 nm to < 470 nm, in particular < 460 nm, for example of > 360 nm to < 460 nm. These radiation sources have been shown to be advantageous for excitation of the material for a wide range of applications.
The material can thereby be provided on the radiation source, in particular a LED chip, as powder layer and/or as monolithic ceramic material layer. Within the scope of another preferred embodiment of the present invention, the light emitting device is a white or blue phosphor converted LED, comprising the material and at least one additional phosphor.
The additional phosphor can thereby be provided on the material according to the invention, in particular on a layer of the material according to the invention, as powder layer and/or as monolithic ceramic material layer.
According to another preferred embodiment of the present invention, the light emitting device is a white phosphor converted LED, comprising the material, a yellow and/or green emitting phosphor, and a red emitting phosphor. This has been shown to be advantageous for a wide range of applications within the present invention since then in combination with a UV - blue emitting LED superior white light sources can be produced.
The yellow and/or green emitting phosphor can thereby for example be selected from the group comprising Ce(III) doped yttrium aluminum garnets (YAG:Ce), SrSi2O2N2IEu or mixtures thereof and/or the red emitting phosphor can be a nitride red phosphor such as (Ca,Sr)SiAlN3:Eu and/or (Ba,Sr,Ca)2SisN8:Eu. The present invention furthermore relates to a material and/or a light emitting device that may be of use in a broad variety of systems and/or applications, amongst them one or more of the following:
Display systems, for example pixelated and/or segmented display systems, 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, 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 subclaims, the figures and the following description of the respective figures and examples, which —in an exemplary fashion— show several embodiments and examples of materials for use in a light emitting device according to the invention as well as several embodiments and examples of a light emitting device according to the invention.
Fig. 1 shows the emission, excitation and reflectance spectrum of
(Bao.75Sr0.23Euo.o2)Si2θ2N2; Fig. 2 shows a diagram of a thermal quenching test with
(Bao.75Sr0.23Euo.o2)Si2θ2N2; Fig. 3 shows emission spectra of (Bao.75Sro.23Euo.o2)Si202N2 for different temperatures;
Fig. 4 shows the XRD powder pattern of (Bao.75Sro.23Euo.o2)Si202N2; Fig. 5 shows the XRD powder pattern of the comparative example
Figure imgf000008_0001
Fig. 6 shows a series of emission spectra comprising the emission spectrum of (Ba0.75Sr0.23Euo.o2)Si202N2 and the emission spectra of the comparative examples of MSi2O2N2 :Eu2+ with M = Sr, Ba, Sro.sBao.s; Fig. 7 shows a schematic crosssectional view of a first embodiment of a light emitting device according to the invention; Fig. 8 shows a schematic crosssectional view of a second embodiment of a light emitting device according to the invention; Fig. 9 shows the emission spectrum of a blue LED with a YAG and a red nitride phosphor and the emission spectrum of (Bao.75Sr0.23Euo.o2)Si2θ2N2;
Fig. 10 shows the emission spectra of two light emitting devices comprising
(Ba0.75Sr0.23Euo.o2)Si2θ2N2 and one comparative light emitting device; and
Fig. 11 shows a scanning electron micrograph of (Bao.75Sro.23Euo.o2)Si2θ2N2 phosphor particles.
The invention will be further understood by the following Example which - in a merely illustrative fashion - shows a material of the present invention. Figs. 1 to 4 refer to (Ba0.75Sr0.23Euo.o2)Si2θ2N2 which was made according to the following:
Blue emitting (Ba0.75Sr0.23Euo.o2)Si2θ2N2 was synthesized by mixing crystalline sub-micron (Bao.7sSro.23Euo.o2)2Si04 and S13N4 in a planetary ball-mill and firing the resulting mixture in reducing N2/H2 (5 %) atmosphere at 1300 -14000C in a molybdenum crucible. After grinding, the intermediate product was refϊred under the same reaction conditions. The raw product was finally ball-milled and screened with a 15 μm sieving gauze.
By means of quantitative elemental analysis, the compositions of two separately synthesized samples have been found to be (Ba0.75Sr0.23Euo.o2)Si2.oθ2.oN2.o and (Bao.74Sro.24Euo.o2)Si2.oθ2.iN2.o, which is (within instrumental uncertainty) in excellent agreement with the chemical formula given above.
To increase the phosphor efficiency, the precursor material synthesized as described above may be mixed with BaCl2 and sintered in N2/H2 (5 %) atmosphere. The resulting powder was washed to remove flux residues and dried.
Fig. 1 shows the emission 1, excitation 2 and reflectance 3 spectrum of (Bao.75Sro.23Euo.o2)Si2θ2N2 phosphor powder. The emission sprectrum 1 shows that
(Bao.75Sro.23Euo.o2)Si2θ2N2 has a narrow emission band with a peak wavelength λmax of -472 nm and a full width at half maximum (FWHM) of ~40 nm. The excitation spectrum 2 indicates a small Stokes Shift and suggests that this phosphor can be efficiently pumped and excited with blue LEDs of > 360 nm to < 460 nm peak wavelength. Fig. 2 shows a diagram of a thermal quenching test with
(Bao.75Sro.23Euo.o2)Si2θ2N2 phosphor powder with the integral emission intensity as a function of the temperature normalized to the room temperature value and with an excitation at 415 nm. The investigations on the thermal quenching behaviour of (Bao.75Sro.23Euo.o2)Si202N2 suggest excellent thermal stability for a wide range of operating conditions. Even at 200 0C 93 % of the initial emission intensity measured at 25 0C is preserved.
Fig. 3 shows emission spectra of (Ba0.75Sr0.23Euo.o2)Si2θ2N2 phosphor powder taken with an excitation at 415 nm at different temperatures ranging from 25 0C up to 330 0C. Reference signs 10, 11, 12, and 13 thereby indicate the data taken at 25 0C, 125 0C, 200 0C, and 330 0C, respectively. Except for a slight broadening (~ 54 nm at 330 0C, 13) no additional shift or change of shape of the spectra can be observed. This shows that (Bao.75Sro.23Euo.o2)Si2θ2N2 is suitable to produce phosphor converted LEDs (pcLEDs) with stable color points that are hardly dependent on operation conditions.
Fig. 4 shows the XRD powder pattern of (Ba0.75Sr0.23Euo.o2)Si2θ2N2 phosphor powder, whereas Fig. 5 shows the XRD powder pattern of the comparative phosphor powder (Bao.98Euo.o2)Si2θ2N2. The X-ray diffraction patterns were thereby measured for powder samples with Cu-Ka radiation and with Bragg-Brentano measuring geometry.
Comparision of Fig. 4 and 5 shows that, although there seems to be a close structural relationship between (Bao.75Sro.23Euo.o2)Si2θ2N2 and (Bao.98Euo.o2)Si2θ2N2, which is indicated by main reflections of (Bao.75Sro.23Euo.o2)Si2θ2N2 appearing at similar diffraction angles compared to (Ba0.98Euo.o2)Si2θ2N2, there are large deviations in relative peak intensities, small but significant shifts of main reflections (for example the two peaks around 2Θ ~25 °) as well as additional peaks observable in the X-ray powder pattern of Fig. 4. These findings suggest that (Ba0.75Sr0.23Euo.o2)Si2θ2N2 is a new phase. Fig. 6 also indicates that (Bao.75Sro.23Euo.o2)Si2θ2N2 is a new phase. Fig. 6 shows a series of emission spectra comprising the emission spectrum of (Bao.75Sro.23Euo.o2)Si2θ2N2 1 and the comparative emission spectra of BaSi2O2N2 :Eu2+ 4, SrSi2O2N2IEu2+ 5, (Bao.5Sro.5)Si202N2:Eu2+ 6 and CaSi2O2N2 :Eu2+ 7. Fig. 6 exhibits that
(Bao.75Sro.23Euo.o2)Si202N2 1 has a quite lower peak wavelegth λmax than the comparative examples BaSi2O2N2 :Eu2+ 4, SrSi2O2N2 :Eu2+ 5, (Bao.5Sro.5)Si202N2:Eu2+ 6 and CaSi2O2N2:Eu2+ 7. Due to the quite different emission spectra of (Ba0.75Sr0.23Euo.o2)Si202N2 1 and the comparative examples BaSi2O2N2 :Eu2+ 4, SrSi2O2N2 :Eu2+ 5 and (Ba0.5Sr0.5)Si2O2N2:Eu2+ 6, the blue emitting (Ba0.75Sr0.23Euo.o2)Si202N2 1 cannot be regarded as a simple solid solution of BaSi2O2N2 :Eu2+ 4 and SrSi2O2N2 :Eu2+ 5. Fig. 7 shows a schematic crosssectional view of a first embodiment of a light emitting device, in particular a phosphor converted light emitting device (pcLED). In this embodiment, the light emitting device comprises a radiation source 21, for example a UV and/or blue radiation source with a peak wavelength < 470 nm, in particular < 460 nm, for example an InGaN LED emitting at > 380 nm to < 440 nm, and a material 22 according to the invention, for example (Bao.75Sro.23Euo.o2)Si2θ2N2. As illustrated in Fig. 7, the radiation source 21 can be for example an LED chip on a submount with bond wires. In the embodiment shown in Fig. 7, the material 22 according to the invention is provided on the radiation source 21, in particular the LED chip, as powder layer and/or as monolithic ceramic material layer. The light emitting device according to this embodiment can emit blue light 23.
Fig. 8 shows a schematic crosssectional view of a second embodiment of a light emitting device, in particular a phosphor converted light emitting device (pcLED). In this embodiment, the light emitting device also comprises a radiation source 21, for example a UV and/or blue radiation source with a peak wavelength < 470 nm, in particular < 460 nm, for example an InGaN LED emitting at > 380 nm to < 440 nm, and a material 22 according to the invention, for example (Bao.75Sro.23Euo.o2)Si2θ2N2. As illustrated in Fig. 8, the radiation source 21 can be for example an LED chip on a submount with bond wires. In the embodiment shown in Fig. 8, the material 22 according to the invention is also provided on the radiation source 21, in particular the LED chip, as powder layer and/or as monolithic ceramic material layer. Furthermore, the light emitting device comprises in this embodiment an additional phosphor 24, for example yellow emitting (Y,Gd)3AlsOi2:Ce (2 %). As shown in Fig. 8, the additional phosphor 24 is in this embodiment provided on the material 22 according to the invention, as powder layer and/or as monolithic ceramic material layer. The light emitting device according to this embodiment can emit blue 23 and for example yellow 25 light.
Fig. 9 shows the emission spectrum of a blue LED emitting at a peak wavelength of 450 nm with a YAG and a red nitride phosphor (full line) 31 and the emission spectrum of (Bao.75Sro.23Euo.o2)Si2θ2N2 (dashed line) 32. Spectrum 31 shows the "cyan gap" at wavelength about 480 nm resulting from a gap between the emission of the blue LED and the yellow/green YAG:Ce phosphor. Spectrum 32 shows that materials according to the invention, for example (Ba0.75Sr0.23Euo.o2)Si2θ2N2, can be used to fill this cyan gap.
Fig. 10 shows the emission spectra of two light emitting devices comprising (Bao.75Sro.23Euo.o2)Si2θ2N2 and one comparative light emitting device. Line 33 (large dashes) thereby shows the emission spectrum of a (Bao.75Sro.23Euo.o2)Si202N2 blue phosphor, YAG:Ce yellow/green phosphor and a CaSiAlN3 :Eu nitride red phosphor., whereas line 34 (small dashes) shows the emission spectrum of a (Ba0.75Sr0.23Euo.o2)Si2θ2N2 blue phosphor, SrSi2O2N2:Eu green phosphor and a CaSiAlN3IEu nitride red phosphor. Line 31 (full line) shows the emission spectrum of the comparative light emitting device with a blue LED emitting at a peak wavelength of 450 nm and with a YAG:Ce yellow/green phosphor and a CaSiAlN3 :Eu red nitride phosphor
Colorimetric data corresponding to these spectra 31, 33, 34 are listed in table 1.
TABLE 1 : Colorimetric data for the spectra 31, 33, 34 in figure 10.
Figure imgf000012_0001
As seen from these data and Fig. 3 the (Ba0.75Sr0.23Euo.o2)Si202N2 phosphor combines high white light quality, in particular high color rendering (Ra: color rendering) and lumen output (LE: lumen equivalent) and high color point stability at elevated temperatures. Additionally, (Bao.7sSro.23Euo.o2)Si202N2 can show a high color point stability with increasing drive currents. Especially in combination with a green emitting SrSi2O2N2IEu phosphor, high-power white light sources with constant color points under demanding operating conditions can be generated.
Furthermore, high quality white light can be generated by using blue LEDs with peak wavelenghts of- 420 nm that are commonly more efficient than LEDs emitting in the 450 nm-470 nm range.
The excitation light of the short wavelength pump LED does not necessarily need to be fully converted into longer wavelength light by the phosphors as depicted in the spectra 33 and 34. In practice, depending on the pump wavelength, for example in case of blue pump LEDs with wavelength of about 380 nm-450 nm, it might be advantageous to allow small amounts of leakage of the pump LED light since by this measure color rendition may further be enhanced.
Fig. 11 shows a scanning electron micrograph of (Ba0.75Sr0.23Euo.o2)Si202N2 phosphor grains. The particular combinations of elements and features in the above detailed embodiments are exemplary only. 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. 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. (BaI-XSrx)Si2O2N2IEu, whereby
0.20 < x < 0.30.
2. Material according to claim 1, whereby the material further comprises a codopant M selected from the group comprising rare earth metals, scandium, yttrium, lanthan, cerium, manganese or mixtures thereof.
3. Material according to claim 1, whereby the doping level of Europium is > 0.1 mol-% to < 10 mol-%, with respect to the stochiometric sum of Barium, Strontium,
Europium and codopant/s M.
4. Material according to claim 1, whereby the doping level of the codopant M is > 0 mol-% to < 5 mol-%, with respect to the stochiometric sum of Barium, Strontium, Europium and codopant/s M.
5. Material according to claim 1, whereby 0.23 < x < 0.27.
6. Use of a material according to claim 1 as a luminescent material.
7. Light emitting device, comprising at least one material according to claim 1.
8. Light emitting device according to claim 7, whereby the material is provided as powder and/or as monolithic ceramic material.
9. Light emitting device according to claim 7, whereby the powder has a mean particle size of > 0.2 μm to < 100 μm.
10. Light emitting device according to claim 7, whereby the monolithic ceramic material has > 90 % of its theoretical density.
11. Light emitting device according to claim 7, whereby the light emitting device comprises a UV and/or blue radiation source with a peak wavelength < 470 nm.
12. Light emitting device according to claim 7, whereby the light emitting device is a white or blue phosphor converted LED, comprising at least one material according to claim 1 , and at least one additional phosphor.
13. Light emitting device according to claim 7, whereby the light emitting device is a white phosphor converted LED, comprising at least one material according to claim 1, a yellow and/or green emitting phosphor, and a red emitting phosphor.
14. Light emitting device according to claim 7, whereby the yellow and/or green emitting phosphor is selected from the group comprising Ce doped yttrium aluminum garnets, SrSi2O2N2IEu or mixtures thereof and/or the red emitting phosphor is a nitride red phosphor.
15. A system comprising a material according to any of the claims 1 to 5 and/or a light emitting device according to any of the claims 7 to 14 and/or making use according to claim 6, the system being used in one or more of the following applications: display systems, 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, warning sign systems, medical lighting application systems, indicator sign systems, and decorative lighting systems portable systems automotive applications green house lighting systems.
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