中国科学院理化技术研究所康雷团队报道了，低结构各向异性能否在PI4AlI4聚焦中产生高光学各向异性的反常巨光学双折射效应。相关研究成果于2025年1月14日发表在《美国化学会杂志》。

具有宽透明度和大二次谐波效应的四面体卤化物，有可能成为具有平衡非线性光学（NLO）特性的中红外宽带隙材料。然而，由于结构各向异性有限，它们的规则四面体基序往往表现出较低的光学双折射（Δn<0.03），这限制了它们的实际相位匹配能力。卤化物结构化学和材料探索的一个重大挑战是提高四面体卤化物的Δn，同时保持其平衡性能。具有低结构各向异性的四面体是否可以产生高光学各向异性的问题仍然没有答案。

该文中，研究人员除了通过增加结构各向异性来增强Δn的传统策略外，还确定了一种以前未报道的通过增加电子各向异性来提高Δn的策略。这种新的策略模型前所未有地提高了现有四面体卤化物PI₄AlI₄的Δn，达到了传统技术无法达到的程度，其值高达0.31@1μm。Δn的异常增加是由阴离子和阳离子四面体基序之间独特的电荷转移效应引起的各向异性电荷再分配实现的。第一性原理分析进一步证实了详细的化学键电子分布和电荷转移图示。据预测，类似的AsI₄AlI₄和TeI₄ZnI₄将表现出更大的巨Δn倾向（>0.5@1μm）。

该发现将极大地丰富sp³杂化四面体的结构化学，并为高双折射结构的设计和调制提供开创性的思路。

附：英文原文

Title: Can Low Structural Anisotropy Produce High Optical Anisotropy Anomalous Giant Optical Birefringent Effect in PI4AlI4 in Focus

Author: Huige Chen, Pifu Gong, Zheshuai Lin, Lei Kang

Issue&Volume: January 14, 2025

Abstract: Tetrahedral halides with broad transparency and large second harmonic effects have the potential to serve as mid-infrared wide-bandgap materials with balanced nonlinear-optical (NLO) properties. However, their regular tetrahedral motifs tend to exhibit low optical birefringence (Δn < 0.03) due to limited structural anisotropy, which constrains their practical phase-matched capability. A significant challenge in halide structural chemistry and material exploration is to enhance the Δn of tetrahedral halides while maintaining their balanced properties. The question of whether tetrahedra with low structural anisotropy can produce high optical anisotropy remains unanswered. In this study, in addition to the conventional strategy of enhancing Δn by increasing structural anisotropy, we identify a previously unreported strategy of enhancing Δn by increasing electronic anisotropy. This novel strategy model unprecedentedly enhances the Δn of an existing tetrahedral halide, PI4AlI4, to a degree not achievable by conventional techniques, with the value reaching up to 0.31@1 μm. The anomalous increase in Δn is achieved by anisotropic charge redistribution resulting from a unique charge transfer effect between the anionic and cationic tetrahedral motifs. First-principles analysis provides further corroboration of the detailed chemical bonding electronic distributions and charge transfer illustrations. It is predicted that analogous AsI4AlI4 and TeI4ZnI4 will exhibit a greater propensity for giant Δn (> 0.5@1 μm). This finding will greatly enrich the structural chemistry of sp3-hybridized tetrahedra and provide seminal ideas for the design and modulation of highly birefringent structures.

DOI: 10.1021/jacs.4c14624

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.4c14624