SrAgAsS 4 : A Noncentrosymmetric Sulfide with Good Infrared Nonlinear Optical Performance Induced by Aliovalent Substitution from Centrosymmetric SrGa 2 S 4 .

A new noncentrosymmetric (NCS) quaternary sulfide, SrAgAsS 4 , was obtained via the strategy of aliovalent substitution based on centrosymmetric (CS) SrGa 2 S 4 . The new compound features two-dimensional [AgAsS 4 ] 2- layers, which are composed of alternately connected [AsS 4 ] tetrahedra and [AgS 4 ] tetrahedra. Importantly, SrAgAsS 4 exhibits a strong phase-matched second-harmonic generation response (1.35 × AgGaS 2 at 2100 nm) and has a suitable birefringence (0.15@2100 nm) and moderate band gap (2.31 eV). The first-principles calculations revealed the significant contribution of [AsS 4 ] and [AgS 4 ] tetrahedra to its optical properties. This work will promote the application of the aliovalent substitution strategy in the design of NCS-structure-based functional materials.