Ternary rare-earth sulfides RE3GaS6 (RE = Ho, Er): Crystal chemistry, second-order nonlinear optical properties and theoretical investigation

Abstract Chalcogenides are extensively studied as infrared nonlinear optical materials, while rare-earth-based ones are scarcely explored. Here, two ternary rare-earth sulfides Ho3GaS6 (1) and Er3GaS6 (2), are obtained by high-temperature solid-state reactions. They are isostructural and crystallize in the orthorhombic noncentrosymmetric space group Cmc21. Their structures can be described as rare earth–S bonds constructed 3D framework, providing tetrahedral cavities for Ga atoms. Their optical band gaps are determined to be 3.03 (1) and 3.08 (2) eV, and their powder samples have no infrared absorption peaks between 400 and 4000 cm–1. Size-dependent second-harmonic generation measurements suggest that both of them are phase-matchable, and have the effects around 0.4 and 0.6 times that of AgGaS2 for their 150–210 μm samples. The structure-property relationship is also studied by structural analysis and theoretical calculations.