Local structural environment and intra-4f transition of rare-earth ion in chalcogenide glass: Comparison between Dy-doped Ge–As–S and Ge–Ga–S glasses

We have employed Dy L3-edge extended X-ray absorption fine structure measurements to investigate the local structures of Dy doped in Ge–As–S and Ge–Ga–S glasses. It turned out that Dy–S distance on average is conspicuously longer in Ge–Ga–S glass despite the number of the nearest neighboring S atoms being nearly identical with each other. The enhanced rare-earth solubility of Ge–Ga–S glass is then explained in connection with decrease in covalence of Ga–S bonds compared with Ge–S or As–S bonds, and structural correlation between GaS4 tetrahedra and Dy. The discrepancy in the local structural environments of trivalent Dy, however, results in no significant changes in the spectral lineshape and the mean energy of its intra-4f-configurational transitions.