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.