The Antiperovskite-Type Oxychalcogenides Ae 3 Q[GeOQ 3 ] (Ae = Ba, Sr; Q = S, Se) with Large Second Harmonic Generation Responses and Wide Band Gaps.

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, Ae 3 Q[GeOQ 3 ] (Ae = Ba, Sr; Q = S, Se), which were synthesized by employing the antiperovskite-type Ba 3 S[GeS 4 ] as the structure template. Their structures feature novel three-dimensinoal frameworks constructed by distorted [QAe 6 ] octahedra, which are further filled by [GeOQ 3 ] tetrahedra to form antiperovskite-type structures. Based on the unique antiperovskite-type structures, the favorable alignment of the polarizable [GeOQ 3 ] tetrahedra and distorted [QAe 6 ] octahedra have been achieved. These contribute the ideal combination of large SHG response (0.7-1.5 times that of AgGaS 2 ), wide E g (3.52-4.10 eV), and appropriate Δn (0.017-0.035) in Ae 3 Q[GeOQ 3 ]. Theoretical calculations and crystal structure analyses revealed that the strong SHG and wide E g could be attributed to the polarizable [GeOQ 3 ] tetrahedra and distorted [QAe 6 ] octahedra. This research provides a new exemplification for the design of high-performance IR NLO materials.