CsSbF2SO4: An Excellent Ultraviolet Nonlinear Optical Sulfate with a KTiOPO4 (KTP)‐Type Structure

A novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF2SO4 was synthesized through an ionothermal synthesis method. A meticulously designed cosubstitution successfully replaced both [TiO6]8‐ and [PO4]3‐ functional groups in KTiOPO4 (KTP) to [SbO4F2]7‐ and [SO4]2‐ units, respectively. The structure of CsSbF2SO4 features a pseudo‐3D framework consisting of interconnecting 1D [SbF2O2SO4]5‐ chains of corner‐sharing [SbO4F2]7‐ octahedra and [SO4]2‐ tetrahedra. The title compound exhibits a sharply enlarged bandgap compared to its parent compound, KTP benefitting from the introduction of F‐ and the displacement of Sb3+ cations. Second‐harmonic generation (SHG) measurements manifested that CsSbF2SO4 is phase‐matchable and reveals strong SHG response of ca. 3.0 × KH2PO4 (KDP), which is the highest value among all of the metal sulfates reported to date. The reported fluoride sulfate is a promising near ultraviolet (UV) nonlinear optical (NLO) material.

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