Synthesis and optical properties of Ga₂S₃-Na₂S-CsCl glasses

Ga₂S₃-Na₂S-CsCl (GNC) glasses were synthesized in open crucibles under inert atmosphere. The evaporative loss of CsCl during glass melting was measured by energy-dispersive X-ray spectroscopy and corrected for by biasing the CsCl concentration in the mixture of starting materials to obtain glasses with accurately controlled stoichiometry. Glass-transition temperatures, refractive-index dispersions, visible and near-infrared transmittance, and band edge energies were measured for four GNC glasses with varying CsCl content, and the respective values were found to significantly improve over earlier studies that did not mitigate CsCl evaporative losses. Glass durability was assessed by a water immersion test at 74 °C. A respective weight loss rate of 39.2 ± 0.3 μg/(cm² h) was found for a GNC glass containing 14 mol% CsCl, indicating good glass durability despite the high CsCl content. The refractive-index dispersion measurements indicate that the Cs⁺ and Cl^- radii are 16% larger in GNC glass than in bulk crystalline CsCl. The band edge energy increases from 2.97 eV in Ga₂S₃-Na₂S glass to 3.32 eV in Ga₂S₃-Na₂S-CsCl glass containing 20 mol% CsCl as a result of introducing Cl^- ions having a large optical electronegativity. The large bandgap of 3.32 eV, the low (450 cm^-1) phonon energy, and the good chemical durability make GNC glass an attractive host material for rare-earth ions with radiative transitions in the near ultra-violet, visible, and near-infrared spectral regions.