基于平面三角形结构基元的硫属红外非线性光学晶体的研究

To deep understand the structure-property relationship and then explore infrared (IR) nonlinear optical (NLO) crystals is always a challenging and hot spots. The π-conjugated planar units possessed large birefringence and polarizability are ideal structural units, such as BO3, CO3 and NO3. Fortunately, in chalcogenides, the d10 transition metals, due to the second-order Jahn−Teller (SOJT) effect, also can form the triangle mode, that provides a new way to design novel IR-NLO crystal materials. In this project, we will focus the chalcogenides containing d10 transition metals with planar triangle modes of MQ3 (Q= S and Se) by solid state reaction and solvothermal methods. Specifically: 1) combining alkali metal or alkaline earth with MQ3 units to synthesis the ternary compounds; 2) combining MQ3 units with M´Q4(M´=Ga and Ge) tetrahedra, and mental with active lone-pairs Pb2+ and Bi3+, to take the advantage of their collaborative effects to increase their IR-NLO coefficients; 3) through systematic exploration, crystals with noncentrosymmetric (NCS) structures will be selected to test the NLO properties; and to modulate the structure and improve the second harmonic generation (SHG) properties, elements replaced method would be used to the system; 4) to combine theoretical calculation, we can summarize the NLO effects of different kinds, density and packing fashion of polar structural units, and further abstract the relationships of structure-NLO. Hence, this project will provide some theoretical support for designing and preparing novel IR-NLO crystal materials with planar triangle units.

从结构-性能的关系角度深刻认识并开发红外非线性光学(IR-NLO)晶体材料一直是NLO领域的难点和热点。具有π共轭体系的平面结构基元，拥有大的双折射率和极化率，是理想的结构单元。在硫属化合物中，d10过渡金属存在次级姜-泰勒效应，也可形成平面三角形构型，为IR-NLO晶体的设计提供新思路。本项目拟通过固相和液相法制备含MQ3(M=Ag+，Cu+和Hg2+；Q=S和Se)结构单元的IR-NLO晶体：1) 结合碱土/碱金属与MQ3单元，合成简单三元化合物，利用碱、碱土金属离子对化合物进行调控；2) MQ3单元结合M′Q4(M′=Ga和Ge)四面体和含独对电子的Pb2+和Bi3+，通过NLO活性基团的协同效应增强非线性性能。3)筛选非心化合物进行粉末倍频测试，结合理论计算，分析此类化合物的结构调控规律以及NLO性能与结构的关系，为含平面结构基元的IR-NLO材料的设计与控制合成提供理论依据。

非线性光学晶体作为激光变频能材料，在扩展激光频率范围方面有着重要的作用。针对红外非线性晶体低激光损伤阈值的问题，我们利用高温固相法在含强共价键的金属硫代磷酸盐体系中展开探索，成功发现两例具有极性空间群的化合物，分别为LiGa2PS6和LiCd3PS6，二者均表现出高激光损伤阈值和大非线性系数，并且LiGa2PS6具有合适的双折射率能够实现相位匹配，而LiCd3PS6在较高温度下存在可逆相变，是一种潜在的非线性开关材料。理论计算发现PS4四面体对二阶非线性系数贡献较大，并且其强的共价键特性有助于提高激光损伤阈值，进一步指出探索新型硫代磷酸盐红外非线性光学材料的重要性。此外，我们还探索了卤素亚碲酸盐、卤素碘酸盐及硼酸盐非线性晶体材料，得到29例结构新颖的化合物，如Ba2[GaF4(IO3)2](IO3)、Li7(TeO3)3和K6NaCaSc2(B5O10)3，并系统表征了其物化性能，分析了功能基团与材料的倍频系数、双折射率及激光损伤阈值等性能之间的关系，对设计和合成新的红外非线性光学材料打下坚实的基础。项目执行中发表包括Angew. Chem. Int. Ed. Chem. Mater. Inorg. Chem.等在内的SCI论文7篇，申请专利1件。