CsSbF 2 SO 4 : An Excellent Ultraviolet Nonlinear Optical Sulfate with a KTiOPO 4 (KTP)‐type Structure

A novel noncentrosymmetric (NCS) polar fluoride sulfate, CsSbF 2 SO 4 , was obtained by ionothermal synthesis. A meticulously designed co‐substitution approach was used to successfully replace the [TiO 6 ] 8− and [PO 4 ] 3− functional groups in KTiOPO 4 (KTP) with [SbO 4 F 2 ] 7− and [SO 4 ] 2− units, respectively. The structure of CsSbF 2 SO 4 features a pseudo‐3D framework consisting of interconnected 1D [SbF 2 O 2 SO 4 ] 5− chains of corner‐sharing [SbO 4 F 2 ] 7− octahedra and [SO 4 ] 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 Sb 3+ cations. Second harmonic generation (SHG) measurements manifested that CsSbF 2 SO 4 is phase‐matchable and revealed a strong SHG response of about 3.0 KH 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.