The Antiperovskite-Type Oxychalcogenides Ae₃Q[GeOQ₃] (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 (Delta n) 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 Ba3S[GeS4] 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 AgGaS2), wide E-g (3.52-4.10 eV), and appropriate Delta n (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.