Rational Design of the Nonlinear Optical Response in a Tin Iodate Fluoride Sn(IO3)2F2

A new tin iodate fluoride, Sn­(IO3)2F2, was meticulously designed based on Sn­(IO3)4 with an intriguing chemical tailoring transformation from the centrosymmetric to noncentrosymmetric structure. Sn­(IO3)2F2 crystallizes in polar space group P21 and features an one-dimensional chain constructed by IO3 and SnO4F2. It has an enlarged band gap (4.08 eV) compared to the Sn­(IO3)4 (3.96 eV) because of the introduction of strong electronegative F–. Also, powder second-harmonic generation (SHG) measurements revealed that Sn­(IO3)2F2 is a phase-matchable nonlinear crystal with a strong SHG response about 3 times that of KH2PO4. Theoretical investigations elaborated that its large nonlinearity originates from the synergistic effect of lone pairs on IO3 and flexible dipole moments of SnO4F2 polyhedra.

一种新型碘酸锡氟化物（tin iodate fluoride）Sn(IO₃)₂F₂，以Sn(IO₃)₄为基础经精准设计，实现了从中心对称到非中心对称结构的化学剪裁转变。Sn(IO₃)₂F₂结晶于极性空间群P2₁，其结构呈现由IO₃与SnO₄F₂构筑的一维链状骨架。相较于Sn(IO₃)₄的3.96 eV带隙，该化合物的带隙拓宽至4.08 eV，这源于高电负性F⁻的引入。此外，粉末二次谐波生成（second-harmonic generation, SHG）测试表明，Sn(IO₃)₂F₂为相位匹配型非线性晶体，其二次谐波响应强度约为磷酸二氢钾（KH₂PO₄）的3倍。理论研究阐明，其显著的非线性光学活性源于IO₃基团上的孤对电子与SnO₄F₂多面体的柔性偶极矩之间的协同增效作用。