Phase equilibria, glass formation and advanced characterization of the Ga2S3–CaF2–CaS system for mid-infrared optical applications

This study investigates the Ga 2 S 3 –CaF 2 –CaS system for mid-infrared optics. The liquidus surface reveals two ternary eutectics (802 and 992 °C). The glass-forming region lies near the Ga 2 S 3 –CaS boundary with 10–40 mol% CaF 2 , improving vitrification. Adding CaF 2 significantly boosts thermal stability: ΔT increases from 97 to 112 °C (binary) to 187–228 °C (ternary). Optical transmission spans ∼520 nm to infrared, with the ternary glasses extending the cutoff from ∼8 μm to ∼10 μm, covering the 8–10 μm atmospheric window due to fluorine-induced phonon modification. Structural analysis confirms [GaS 4 ] tetrahedral order and fluoride acting as a network modifier. These fluorosulfide glasses offer enhanced stability, formability and extended infrared transparency, making them promise for thermal imaging, chemical sensing and laser guidance systems.