The pursuit of second-order nonlinear optical (NLO) materials for mid-infrared (mid-IR, 3–5 μm) applications has been a significant research frontier due to their potential in optoelectronic technologies. In this review, we focus on noncentrosymmetric (NCS) molybdenum/tungsten tellurites incorporating d0 transition metal cations (Mo6+/W6+) and Te4+ cation with stereo-chemically active lone electron pair, which are prone to the second-order Jahn-Teller (SOJT) distortions. These compounds exhibit exceptional NLO effects, high optical transmittance in the 3–5 μm range, moderate birefringence, and ease of crystal growth in ambient conditions. Furthermore, they possess wider band gaps compared to conventional mid-IR NLO materials like metal phosphides and chalcogenides, enhancing their laser damage resistances. We categorize the notable NCS molybdenum/tungsten tellurites into nine series based on their cationic types, concentrating on ternary and quaternary systems. The review outlines their synthesis methods, crystal structures, growth techniques, and physical properties, with an emphasis on the relationship between SOJT-active units, NCS structures, and NLO performances. This work provides a clear perspective on the understanding of these materials and aims to accelerate the exploration of high-performance mid-IR NLO crystals to meet the increasing technological demands.

中文翻译：

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非线性光学亚碲钼/亚碲钨的研究进展：结构、晶体生长和表征


由于二阶非线性光学 （NLO） 材料在光电技术中的潜力，因此寻求用于中红外 （mid-IR， 3–5 μm） 应用的二阶非线性光学 （NLO） 材料一直是一个重要的研究前沿。在这篇综述中，我们重点介绍了掺入 d0 过渡金属阳离子 （Mo6+/W6+） 和 Te4+ 阳离子与立体化学活性孤电子对的非中心对称 （NCS） 钼/碲钨，它们容易发生二阶 Jahn-Teller （SOJT） 畸变。这些化合物表现出出色的 NLO 效应、3–5 μm 范围内的高透光率、适度的双折射以及在环境条件下易于晶体生长。此外，与传统的中红外非线性光球材料（如金属磷化物和硫化物）相比，它们具有更宽的带隙，增强了其抗激光损伤能力。我们根据其阳离子类型将著名的 NCS 钼/碲钨矿分为九个系列，集中在三元和四元系统。综述概述了它们的合成方法、晶体结构、生长技术和物理性质，重点介绍了 SOJT 活性单元、NCS 结构和 NLO 性能之间的关系。这项工作为理解这些材料提供了清晰的视角，旨在加速高性能中红外 NLO 晶体的探索，以满足日益增长的技术需求。