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Luminescence and Valence of Tb Ions in Alkaline Earth Stannates and Zirconates Examined by X-ray Absorption Fine Structures.

ABSTRACT

The difference in Tb(3+) green luminescence intensities in doped perovskite(ABO3)-type alkaline earth stannates, AeSnO3 (Ae = Ca, Sr, Ba), and the Mg codoping effect on the luminescence intensities in doped CaMO3 (M = Sn, Zr) were investigated utilizing the X-ray absorption fine structures (XAFS) of the Tb LIII absorption edge. It is considered that the local symmetry at A sites is responsible for the different Tb(3+) luminescence intensities in AeSnO3 (Ae = Ca, Sr, Ba) doped with Tb ions at A sites. However, it was found from the XAFS spectra that some Tb ions are unintentionally stabilized at B sites as Tb(4+), especially in BaSnO3. Not only the central symmetry for Tb(3+) at A sites but also the presence of Tb(4+) at B sites were considered to bring about the absence of Tb(3+) luminescence in doped cubic BaSnO3. No obvious changes in the Tb(3+) local structure at A sites were detected between Tb single doped and Tb-Mg codoped CaMO3 (M = Sn, Zr) from the extended XAFS oscillation, but the trace of Tb(4+) at B sites in the Tb single doped sample was observed in the X-ray absorption near edge structures. It is, therefore, considered that the Tb(3+) luminescence enhancement by Mg codoping is primarily attributed to the charge compensation rather than the changes in the local structure around Tb(3+) at A sites.