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Title: XAFS Analysis of Local Structure around Ce in Ca3Sc2Si3O12:Ce Phosphor for White LEDs

Abstract

We have studied the local structure around Ce atom in Ca3Sc2Si3O12 host crystal, which has been developed as a new green phosphor for white light emitting diodes (LEDs). As the local structure and chemical environment of the dopant atom are very important to improve the performance of the phosphor, we have used XAFS to get chemical and structural information around the Ce dopant. The XANES spectrum of the Ce LIII-edge reveals that the Ce atom is trivalent in Ca3Sc2Si3O12. There are two kinds of possible Ce substitution sites, Ca site and Sc site, in garnet type Ca3Sc2Si3O12 crystal structure. The Ce atom is found to be at the Ca site in the host crystal by the comparison of the Fourier transform of Ce K-edge EXAFS spectrum with those of Ca and Sc K-edge EXAFS spectra. The theoretical analysis with FEFF also clarified the Ce substitution at the Ca site. Furthermore, the result of the analysis indicates the structural disorder around Ca and Si atoms at 3.75 A. It is possible that there are some defects around the Ca and Si atoms at 3.75 A to compensate the excess positive charge by introduced Ce3+ at the Ca2+ site.

Authors:
; ; ; ;  [1];  [2]
  1. Mitsubishi Chemical Group Science and Technology Research Center, Inc, 1000 Kamoshida-cho, Aoba-ku, Yokohama 227-8502 (Japan)
  2. Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Hyogo 679-5198 (Japan)
Publication Date:
OSTI Identifier:
21054633
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal Issue: 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644534; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; CERIUM ADDITIONS; COMPARATIVE EVALUATIONS; CRYSTAL STRUCTURE; CRYSTALS; FINE STRUCTURE; FOURIER TRANSFORMATION; GARNETS; LIGHT EMITTING DIODES; PERFORMANCE; PHOSPHORS; SCANDIUM SILICATES; X-RAY SPECTRA; X-RAY SPECTROSCOPY

Citation Formats

Akai, Toshio, Shigeiwa, Motoyuki, Okamoto, Kaoru, Shimomura, Yasuo, Kijima, Naoto, and Honma, Tetsuo. XAFS Analysis of Local Structure around Ce in Ca3Sc2Si3O12:Ce Phosphor for White LEDs. United States: N. p., 2007. Web. doi:10.1063/1.2644534.
Akai, Toshio, Shigeiwa, Motoyuki, Okamoto, Kaoru, Shimomura, Yasuo, Kijima, Naoto, & Honma, Tetsuo. XAFS Analysis of Local Structure around Ce in Ca3Sc2Si3O12:Ce Phosphor for White LEDs. United States. doi:10.1063/1.2644534.
Akai, Toshio, Shigeiwa, Motoyuki, Okamoto, Kaoru, Shimomura, Yasuo, Kijima, Naoto, and Honma, Tetsuo. Fri . "XAFS Analysis of Local Structure around Ce in Ca3Sc2Si3O12:Ce Phosphor for White LEDs". United States. doi:10.1063/1.2644534.
@article{osti_21054633,
title = {XAFS Analysis of Local Structure around Ce in Ca3Sc2Si3O12:Ce Phosphor for White LEDs},
author = {Akai, Toshio and Shigeiwa, Motoyuki and Okamoto, Kaoru and Shimomura, Yasuo and Kijima, Naoto and Honma, Tetsuo},
abstractNote = {We have studied the local structure around Ce atom in Ca3Sc2Si3O12 host crystal, which has been developed as a new green phosphor for white light emitting diodes (LEDs). As the local structure and chemical environment of the dopant atom are very important to improve the performance of the phosphor, we have used XAFS to get chemical and structural information around the Ce dopant. The XANES spectrum of the Ce LIII-edge reveals that the Ce atom is trivalent in Ca3Sc2Si3O12. There are two kinds of possible Ce substitution sites, Ca site and Sc site, in garnet type Ca3Sc2Si3O12 crystal structure. The Ce atom is found to be at the Ca site in the host crystal by the comparison of the Fourier transform of Ce K-edge EXAFS spectrum with those of Ca and Sc K-edge EXAFS spectra. The theoretical analysis with FEFF also clarified the Ce substitution at the Ca site. Furthermore, the result of the analysis indicates the structural disorder around Ca and Si atoms at 3.75 A. It is possible that there are some defects around the Ca and Si atoms at 3.75 A to compensate the excess positive charge by introduced Ce3+ at the Ca2+ site.},
doi = {10.1063/1.2644534},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
  • Gadolinium or lanthanum co-doped (0.5 mole) yttrium aluminum garnet doped with cerium phosphors were synthesized by a citric acid gel method and the effect of co-dopants on the structural and luminescent properties were studied. A significant peak shift in the photoluminescence spectra of yttrium aluminum garnet doped cerium was observed from 535 to 556 and 576 nm for gadolinium or lanthanum co-doped phosphors, respectively. The color tuned phosphor were blended with yttrium aluminum garnet doped cerium which showed a considerable improvement in the Commission International De Eclairage chromaticity co-ordinate values of gallium nitride based blue light emitting diode pumped whitemore » light. White light emitted from yttrium aluminum garnet doped cerium shows a Commission International De Eclairage value of (0.229, 0.182) whereas the yttrium aluminum garnet doped cerium phosphor blended with gadolinium or lanthanum co-doped phosphor shows (0.262, 0.243) and (0.295, 0.282), respectively. These results demonstrate the possibility to use these phosphor blends to enhance the white light generation in the field of white-light emitting diode solid-state lighting.« less
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