From Mid-Infrared Luminescence to Laser Gain in Chalcogenide Glasses and Glass-Ceramics

Mid-infrared (MIR) lasers operating in the 2–6 μm 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 3+ -, Ce 3+ -, and Pr 3+ -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 2+ -, Co 2+ -, Fe 2+ -, and Ni 2+ -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.