Oxygen-Substitution Induced High-Performance Nonlinear Optical Properties: Witnessed by the First Quaternary Oxythiostannate

Oxychalcogenides can combine the large second-harmonic generation (SHG) effects of chalcogenides with the wide bandgaps of oxides to obtain high-performance infrared (IR) nonlinear optical (NLO) crystal materials. Here, the first quaternary oxythiostannate NLO crystal material Sr₆Sn₃OS₁₁ crystallized in the trigonal noncentrosymmetric space group P3m1 is synthesized by a high-temperature solid-state method. Its 0D structure features isolated [SnS₄] and [SnOS₃] tetrahedra, which can be derived from parent 0D Sr₂SnS₄ (Ama2) via anion partial substitution. The SHG response of Sr₆Sn₃OS₁₁ primarily contributed by [SnS₄] tetrahedra is increased to be 0.82 × benchmark AgGaS₂ compared with 0.5 × AgGaS₂ for Sr₂SnS₄. The experimental bandgap of Sr₆Sn₃OS₁₁ is 2.81 eV, which is mainly determined by the Sr 4d and S 3p orbitals according to the theoretical calculation results. This work not only expands oxythiostannates as promising IR NLO materials but also contributes a facile strategy to improve the NLO properties from known ones.