含孤对电子非对称单元新型硫代硼酸盐类红外材料探索合成

Borates are an important kind of photoelectric functional materials, and have wide applications in the fields of nonlinear optics, laser materials, laser spectroscopy, communications, medical applications, etc. However, the strong B-O covalent bonds and hence the multi-phonon absorption make their IR cut-off edges are usually located around near-IR region. This project is mainly based on the relationships between the crystal structures and their optical properties.And together with the method of design and control of microstropic structure in the view of the molecular engineering, we proposed the thought of substituting the element of sulfur for oxygen in the borates, coorparating with lone-pairs asymmetric units with large dipole moments. Using the high temperature solid-state synthesis route under water- and oxygen-free conditions in evacuated sealed tubes we attempted to synthesize new types of photoelectronic functional thioborate compounds with excellent mid- and far-IR optical transparency, determine the crystal structures, and measure the UV/Vis/NIR absorption spectra and the thermal stability of the compounds synthesized. We will perform the calculations of the electronic structure, density of states, and optical properties, and find the key structural units which are sensitive to their optical properties. Moreover, we also modify the structural units chemically and regulate them structurally, so as to achieve rational design and controllable synthesis of thioborate compounds, providing scientific bases for research and development of new IR nonlinear optical crystalline materials.

硼酸盐是一类重要的非线性光学晶体材料，在紫外、可见光波段应用广泛。然而由于强的硼-氧共价键引起的多声子吸收，该类化合物的红外截止边通常处在近红外波段附近。本研究课题基于对晶体结构-光学性能关系和阴离子基团理论的理解，结合分子工程学中微观结构基元设计与调控的方法，提出将硼酸盐中半径较小的氧阴离子用半径较大的硫阴离子替换，引入偶极矩较大的含孤对电子非对称结构单元，通过无水、无氧条件下真空封管高温固相合成的途径，设计合成具有良好中远红外透过性能的新型非线性光学晶体，测定化合物的晶体结构、紫外/可见/近红外吸收光谱、热稳定性能等，并对化合物的电子能带结构、态密度及光学性质进行理论计算和分析，确定晶体结构中对材料的光学性能起关键作用的结构敏感基元，并对其进行化学修饰或结构调控，以期实现对硫代硼酸盐体系化合物的合理设计和可控合成，为新型中远红外非线性光学晶体材料的研究开发提供科学依据。

本课题采用高温固相、中低温溶液法合成法，首次探索得到了数例新型光学晶体材料，结合单晶及粉末x射线衍射、紫外-可见-近红外吸收光谱技术、热重及差热、Kurtz-Perry粉末倍频及第一性原理计算方法表征和分析了所得材料的基本物化特性、电子结构及成键机理，诊断出了对光诱导较为敏感的结构基元。以含孤对电子的原子为主要光敏感基团，并通过引入卤素部分替换硫属阴离子调控原子基团畸变程度，增大形成非心空间群的几率，并增强它们的局域电偶极矩，获得了多个具有非中心对称结构的新型非线性光学晶体。同时本课题还研究发现，引入卤素元素可增大光学吸收带隙，提升材料的紫外透光范围，降低声子能减小材料对泵浦基频光的吸收，为进一步探索卤素混合阴离子硫化物体系宽带隙新型红外光学晶体材料提供探索方向。