The Antiperovskite-Type Oxychalcogenides Ae₃ Q[GeOQ₃ ] (Ae = Ba, Sr; Q = S, Se) with Large Second Harmonic Generation...

Oxychalcogenides capable of exhibiting excellent balance among large second-harmonic generation (SHG) response, wide band gap (E_g ), and suitable birefringence (Δn) are ideal materials class for infrared nonlinear optical (IR NLO) crystals. However, rationally designing a new high-performance oxychalcogenide IR NLO crystal still faces a huge challenge because it requires the optimal orientations of the heteroanionic groups in oxychalcogenide. Herein, a series of antiperovskite-type oxychalcogenides, Ae₃ Q[GeOQ₃ ] (Ae = Ba, Sr; Q = S, Se), which were synthesized by employing the antiperovskite-type Ba₃ S[GeS₄ ] as the structure template. Their structures feature novel three-dimensinoal frameworks constructed by distorted [QAe₆ ] octahedra, which are further filled by [GeOQ₃ ] tetrahedra to form antiperovskite-type structures. Based on the unique antiperovskite-type structures, the favorable alignment of the polarizable [GeOQ₃ ] tetrahedra and distorted [QAe₆ ] octahedra have been achieved. These contribute the ideal combination of large SHG response (0.7-1.5 times that of AgGaS₂ ), wide E_g (3.52-4.10 eV), and appropriate Δn (0.017-0.035) in Ae₃ Q[GeOQ₃ ]. Theoretical calculations and crystal structure analyses revealed that the strong SHG and wide E_g could be attributed to the polarizable [GeOQ₃ ] tetrahedra and distorted [QAe₆ ] octahedra. This research provides a new exemplification for the design of high-performance IR NLO materials.