Quaternary alkaline-earth metal thiophosphate SrAgPS 4 : syntheses, structures, and optical properties.

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, SrAgPS 4 , was obtained via a high-temperature solid-state method. The new compound crystallizes in the NCS Ama 2 (No. 40) space group and features two-dimensional [AgPS 4 ] 2- layers consisting of alternately connected [PS 4 ] and [AgS 4 ] tetrahedra. SrAgPS 4 exhibits a strong phase-matched second harmonic generation response (1.10 × AgGaS 2 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.