Strategic Oxygen‐Substitution in Perfluorinated Ce(IV) Coordination Frameworks Triggers Dual‐Wavelength Nonlinear Optical Materials With Exceptional Performances

Abstract Nonlinear optical (NLO) crystals with second‐harmonic generation (SHG) are crucial in laser technology for extending spectral ranges. However, achieving large SHG coefficients, suitable birefringence for phase‐matching, and a broad laser output range remains a significant challenge. This work put forward a facile route to create NLO crystals with a wide‐wavelength range by a slight oxygenation strategy in Ce(IV)‐based fluorides. Given the tendency of perfluorinated Ce(IV)‐based polyhedral geometry unit, a divalent oxygen anion was introduced to partially replace the monovalent fluorine anion to enhance the distortion of Ce(IV)‐based polyhedra. This work successfully synthesized a series of acentric Ce(IV)‐based oxyfluorides, ACe 3 OF 11 (A = NH 4 , K, Rb), starting from noncentrosymmetric NH 4 Ce 3 F 13 as the parent structure. ACe 3 OF 11 exhibits strong SHG responses of 3.4∼5.2 times that of KH 2 PO 4 at 1064 nm and 0.14∼0.62 times of AgGaS 2 at 2100 nm, a wide phase‐matching range from ultraviolet to infrared wavelength regions, which are unprecedented for rare‐earth oxyfluoride crystals. This work establishes a partial oxygenation strategy for designing NLO rare‐earth oxyfluorides, delivering novel NLO candidates with an optimized balance between wide bandgap, strong SHG efficiency, and unprecedented broadband phase‐matching capability.