Tin Chloride Sulfates A3Sn2(SO4)3-xCl1+2x (A = K, Rb, Cs; x=0, 1) as Multifunctional Optical Materials

The series of alkali-metal tin chloride sulfates A(3)Sn(2)(SO4)(3),Cl1+2x (A = K, Rb, Cs; x = 0, 1), K3Sn2(SO4)(3)Cl, Rb3Sn2(SO4)(2)Cl-3, and Cs3Sn2(SO4)(2)Cl-3, 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)(3)Cl being noncentrosymmetric, while Rb3Sn2(SO4)(2)Cl-3 and Cs3Sn2(SO4)(2)Cl-3 are centrosymmetric. Powder second-harmonic generation (SHG) measurements indicate that K3Sn2(SO4)(3)Cl is a nonlinear optical material that is type I phase matchable with a weak SHG response (0.1x 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.