Na₃SiS₃F: A Wide Bandgap Fluorothiosilicate with Unique [SiS₃F] Unit and High Laser‐Induced Damage Threshold

Abstract The exploration of antilaser damage wide bandgap infrared (IR) nonlinear optical (NLO) materials is urgent but challenging. Herein, by introducing the idea of fluorination into chalcogenides, a wide bandgap IR NLO material Na₃SiS₃F with unprecedented [SiS₃F] tetrahedra is designed and synthesized. Na₃SiS₃F shows a wide bandgap of 4.75 eV (the largest one in the reported quaternary metal chalcogenides), resulting in a high laser damage induced threshold of ≈5 × AgGaS₂ (AGS). Meanwhile, the compound has a moderate NLO response (≈0.3 ×AGS) with phase‐matching behavior, large birefringence (0.15@1064 nm), and wide IR transparent region. The introduction of fluorine breaks the structural symmetry and broadens the highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gap, polarizability anisotropy, and hyperpolarizability of the Si–S tetrahedral unit. The results indicate that Na₃SiS₃F is a promising IR NLO material for the high‐power laser application and open an avenue for the design of new wide bandgap IR NLO materials based on NLO‐active [SiS_xF_4−x] (x = 1, 2, 3) mixed anionic tetrahedral group.