Emission properties and local structure of Tm3+ in Ge–Ga–S–Br glass

Spectroscopic properties of Tm3+ in (1 − x) (Ge0.25Ga0.10S0.65)–xBr (or CsBr) glasses (x = 0.0 and 0.1) were investigated. Emission properties of Tm3+ in 0.9(Ge0.25Ga0.10S0.65)–0.1Br glass were similar to those in Ge0.25Ga0.10S0.65 glass, while there was significant improvement when doped into 0.9(Ge0.25Ga0.10S0.65)–0.1CsBr glass. The lifetime of the Tm3+:3H4 level increased from 0.23 to 1.22 msec with 10 mol% CsBr addition. The presence of Cs+ facilitated the formation of [GaS3/2Br]− units by donating an electron to the Ga tetrahedron, resulting in the homogeneous distribution of Br. In this way, Tm3+ ions have their local environment made of Br only. When Br ions were added instead of CsBr, [GaS(4−x)/2Br]− units with x > 1 were formed and Tm3+ ions were surrounded by both S and Br, producing a high phonon environment.