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

Abstract 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.