Tin Chloride Sulfates A3Sn2(SO4)3–x Cl1+2x (A = K, Rb, Cs; x = 0, 1) as Multifunctional Optical Materials

The series of alkali-metal tin chloride sulfates A3Sn2(SO4)3–x Cl1+2x (A = K, Rb, Cs; x = 0, 1), K3Sn2(SO4)3Cl, Rb3Sn2(SO4)2Cl3, and Cs3Sn2(SO4)2Cl3, were successfully synthesized through an improved mild hydrothermal method. Interestingly, in addition to the cation size effect, the structure-directing effect of anions induces different symmetries in the three title compounds, with K3Sn2(SO4)3Cl being noncentrosymmetric, while Rb3Sn2(SO4)2Cl3 and Cs3Sn2(SO4)2Cl3 are centrosymmetric. Powder second-harmonic generation (SHG) measurements indicate that K3Sn2(SO4)3Cl is a nonlinear optical material that is type I phase matchable with a weak SHG response (0.1× KDP). Photoluminescence tests reveal that the three title compounds emit strong greenish yellow, orange, and salmon light, respectively, under UV excitation, indicating that they are promising inorganic solid fluorescent materials. Simultaneously, a detailed structural analysis of all the known tin­(II) halide sulfates has been performed, which will guide the systematic exploration of high-performance tin­(II)-based functional materials in the future.