From mid-infrared luminescence to laser gain in chalcogenide glasses and glass-ceramics

Mid-infrared (MIR) lasers operating in the 2–6[Formula: see text][Formula: see text]m region are important for spectroscopy, sensing, communications, medicine, lidar, and electro-optical applications. Chalcogenide glasses and glass–ceramics are attractive MIR gain-media candidates because of their broad infrared transparency and low-phonon-energy hosts. This review focuses on recent progress in chalcogenide glasses and glass–ceramics toward practical MIR laser operation. Rare-earth-doped glasses and fibers are discussed from early MIR emission studies to recent Tb[Formula: see text]-, Ce[Formula: see text]-, and Pr[Formula: see text]-based laser demonstrations, with particular attention to low-loss fibers. For rare-earth-doped glass–ceramics, dopant partitioning among nanocrystals and glass–crystal interfaces is examined as a key factor governing spectroscopic performance. Transition-metal-doped systems, including Cr[Formula: see text]-, Co[Formula: see text]-, Fe[Formula: see text]-, and Ni[Formula: see text]-activated materials, are reviewed with emphasis on crystal-field engineering and crystallization-induced optical loss. Bulk, fiber, waveguide, and microcavity platforms are further compared in terms of gain–loss balance and their suitability for practical MIR laser operation.