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

Abstract Spectroscopic properties of Tm 3+ in (1 − x ) (Ge 0.25 Ga 0.10 S 0.65 )– x Br (or CsBr) glasses ( x = 0.0 and 0.1) were investigated. Emission properties of Tm 3+ in 0.9(Ge 0.25 Ga 0.10 S 0.65 )–0.1Br glass were similar to those in Ge 0.25 Ga 0.10 S 0.65 glass, while there was significant improvement when doped into 0.9(Ge 0.25 Ga 0.10 S 0.65 )–0.1CsBr glass. The lifetime of the Tm 3+ : 3 H 4 level increased from 0.23 to 1.22 msec with 10 mol% CsBr addition. The presence of Cs + facilitated the formation of [GaS 3/2 Br] − units by donating an electron to the Ga tetrahedron, resulting in the homogeneous distribution of Br. In this way, Tm 3+ ions have their local environment made of Br only. When Br ions were added instead of CsBr, [GaS (4− x )/2 Br] − units with x > 1 were formed and Tm 3+ ions were surrounded by both S and Br, producing a high phonon environment.