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 Å. It is possible that there are some defects around the Ca and Si atoms at 3.75 Å to compensate the excess positive charge by introduced Ce3+ at the Ca2+ site.