Quaternary alkaline-earth metal thiophosphate SrAgPS4: syntheses, structures, and optical properties

Abstract

Metal thiophosphates have outstanding properties for the generation of mid-infrared coherent light and are an emerging nonlinear optical material system. In this study, a new non-centrosymmetric (NCS) quaternary alkaline-earth metal thiophosphate, SrAgPS₄, was obtained via a high-temperature solid-state method. The new compound crystallizes in the NCS Ama2 (No. 40) space group and features two-dimensional [AgPS₄]²⁻ layers consisting of alternately connected [PS₄] and [AgS₄] tetrahedra. SrAgPS₄ exhibits a strong phase-matched second harmonic generation response (1.10 × AgGaS₂ at 2100 nm) and a large band gap (2.97 eV). In addition, theoretical calculations reveal the intrinsic relationship between the electronic structure and optical properties. This work enriches and greatly promotes the research on infrared nonlinear optical materials based on thiophosphates.