Polar Antiperovskite Oxides: Promising Mid-Infrared Nonlinear Optical Materials with Strong Second-Harmonic Generation

Despite significant advances in nonlinear optical (NLO) materials, a systematic strategy for designing mid-infrared (mid-IR) NLO oxides that simultaneously exhibit strong second-harmonic generation (SHG) efficiency and wide optical transparency remains elusive. Herein, we report two polar antiperovskite oxide materials, (Pb1.5Cd1.5)GeO5 (PCGO) and Pb3GeO5 (PGO). Structural analyses reveal that PCGO adopts a 2H-hexagonal antiperovskite structure, whereas PGO features a three-dimensional antiperov