1.48 μm emission properties and the cross-relaxation mechanism in chalcohalide glass doped with Tm

1.48 μm emission properties and the cross-relaxation mechanism of Tm³⁺ ions in 0.7(Ge_0.25As_0.10S_0.65) + 0.15GaS_3/2 + 0.15CsBr glass were investigated. Both the relative intensity ratio of the 1.48 μm emission to 1.82 μm and the measured lifetime of the ³H₄ level decreased with increasing Tm³⁺ concentration. When temperature decreased from room temperature to 20 K, lifetimes of the ³H₄ level increased from 670 to 970 μs. At the same time, the critical distance for cross-relaxation decreased from 1.11 to 0.93 nm. These results indicate that cross-relaxation (³H₄, ³H₆ → ³F₄, ³F₄) became less effective as temperature decreased. Analysis of the temperature dependence of cross-relaxation rates showed that cross-relaxation in Tm³⁺ is a phonon-assisted energy transfer process. The major phonon contributing to the process is from the Ga-Br vibration in GaS_3/2Br]⁻ units.