Fabrication of chalcohalide glass ceramics containing BaCl₂: Er³⁺ crystals for 3.1 µm mid‐infrared luminescence

The growing demand for high‐performance mid‐infrared (MIR) light sources has stimulated the development of rare earth ions activated chalcohalide glass ceramics (GCs). Herein, Er 3+ ‐doped GeS 2 –Ga 2 S 3 –CsCl–BaCl 2 chalcohalide glasses were fabricated via melt‐quenching, which shows good transparency spanning from visible to the MIR region. The controllable precipitation of BaCl 2 crystals through thermal annealing provides a low‐phonon‐energy environment for Er 3+ doping. Spectroscopic analysis demonstrates that Er 3+ ions preferentially partition into BaCl 2 , resulting in suppression of non‐radiative relaxation and enabling the appearance of uncommon emission lines of Er 3+ . Remarkably, in addition to 2.7 µm MIR emission, 3.1 µm MIR emission attributed to the Er 3+ : 4 S 3/2 → 4 F 9/2 transition was first reported in the chalcohalide glass system.