Enhancement of the 1.31-μm emission properties of Dy³⁺-doped Ge–Ga–S glasses with the addition of alkali halides

Alkali halides such as KBr, KI, CsBr, and C_sI were added to Dy³⁺-doped Ge–Ga–S glasses, and their effects on the 1.31-μm emission property were investigated. The intensities of the 1.31-μm emission (⁶F_11/2 · ⁶H_9/2 → ⁶H_15/2) increased at the expense of the 1.75-μm emission intensity (⁶H_11/2 → ⁶H_15/2) with the alkali halide addition. The lifetimes of the 1.31-μm emission level also increased as much as 35 times from 38 μs for Ge–Ga–S glass to 1320 μs for the glass containing 10 mol% CsBr. These enhancements occurred only when the ratio of MX (M = K, Cs; X = Br, I)/Ga was equal to or larger than unity. Raman spectra of Ge–Ga–S–CsBr glasses indicated the formation of [GaS_3/2Br]⁻ complexes, which provide the preferred sites for Dy³⁺. Due to this new local environment of Dy³⁺, the multiphonon relaxation rates from the Dy³⁺:⁶F_11/2 · ⁶H_9/2 level decreased by approximately four orders of magnitude. The enhancement in the 1.31-μm emission properties with alkali halide addition supports the potentials of these glasses as hosts for the Dy³⁺-doped fiber-optic amplifiers.