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

The difference in Tb green luminescence intensities in doped perovskite(ABO)-type alkaline earth stannates, AeSnO (Ae = Ca, Sr, Ba), and the Mg codoping effect on the luminescence intensities in doped CaMO (M = Sn, Zr) were investigated utilizing the X-ray absorption fine structures (XAFS) of the Tb L absorption edge. It is considered that the local symmetry at A sites is responsible for the different Tb luminescence intensities in AeSnO (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, especially in BaSnO. Not only the central symmetry for Tb at A sites but also the presence of Tb at B sites were considered to bring about the absence of Tb luminescence in doped cubic BaSnO. No obvious changes in the Tb local structure at A sites were detected between Tb single doped and Tb-Mg codoped CaMO (M = Sn, Zr) from the extended XAFS oscillation, but the trace of Tb 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 luminescence enhancement by Mg codoping is primarily attributed to the charge compensation rather than the changes in the local structure around Tb at A sites.