Strategic Oxygen-Substitution in Perfluorinated Ce(IV) Coordination Frameworks Triggers Dual-Wavelength Nonlinear...

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, ACe₃OF₁₁ (A = NH₄, K, Rb), starting from noncentrosymmetric NH₄Ce₃F₁₃ as the parent structure. ACe₃OF₁₁ exhibits strong SHG responses of 3.4∼5.2 times that of KH₂PO₄ at 1064 nm and 0.14∼0.62 times of AgGaS₂ 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.