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

A novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF2 SO4 , 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 [SbO4 F2 ]7- and [SO4 ]2- units, respectively. The structure of CsSbF2 SO4 features a pseudo-3D framework consisting of interconnected 1D [SbF2 O2 SO4 ]5- chains of corner-sharing [SbO4 F2 ]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 CsSbF2 SO4 is phase-matchable and revealed a strong SHG response of about 3.0 KH2 PO4 (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.