CsSbF2SO4: An Excellent Ultraviolet Nonlinear Optical Sulfate with a KTiOPO4 (KTP)-type Structure

A novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF2SO4, was obtained by ionothermal synthesis. A meticulously designed co-substitution approach was used to successfully replace the [TiO6](8-) and [PO4](3-) functional groups in KTiOPO4 (KTP) with [SbO4F2](7-) and [SO4](2-) units, respectively. The structure of CsSbF2SO4 features a pseudo-3D framework consisting of interconnected 1D [SbF2O2SO4](5-) chains of corner-sharing [SbO4F2](7-) octahedra and [SO4](2-) tetrahedra. The title compound exhibits a sharply enlarged band gap compared to its parent compound, KTP, benefitting from the introduction of F- ions and the displacement of Sb3+ cations. Second harmonic generation (SHG) measurements manifested that CsSbF2SO4 is phase-matchable and revealed a strong SHG response of about 3.0KH(2)PO(4) (KDP), which is the highest value reported for any metal sulfate reported to date. The reported fluoride sulfate is a promising near ultraviolet (UV) nonlinear optical (NLO) material.