[HgX <sub>2</sub> ] Linear Group Enabled Ultraviolet Birefringent Crystal RbHg <sub>5</sub> Br <sub>11</sub> with Strong Optical Anisotropy and Wide Bandgap
Yingtai Du, Wangfei Che, Yunfei Shi, Juanjuan Lu, Xiaodong Zhou, Ting Liu, Shilie Pan, Junjie Li
Abstract
Abstract Birefringent crystals are pivotal for modern optical modulation technologies, yet developing high‐performance birefringent materials with large birefringence (Δ n ), wide bandgaps, and scalable synthesis remains a significant challenge. Different from the traditional planar [MQ 3 ] and distorted [MQ n ] (n ≥ 4) polyhedral units, a “linear‐group” design strategy is proposed, targeting heavy‐metal halides with [HgX 2 ] (X = halides) coordination modes to exploit their inherent polarizability anisotropy. Through systematic experimental investigations in the ternary A‐Hg‐X (A = Rb, Cs; X = Br, I) system, six novel Hg‐based halides were synthesized. Notably, RbHg 5 Br 11 with linear [HgBr 2 ] units demonstrates excellent optical properties, including a wide bandgap (3.73 eV) and large Δ n ( cal. ) (0.35@546 nm). Importantly, the compound displays a good crystal growth habit, and the high‐quality RbHg 5 Br 11 single crystal can be grown by the simple solution method. Theoretical calculations reveal that the strong optical anisotropy arises from the aligned [HgBr 2 ] linear units. The results demonstrate that RbHg 5 Br 11 is a promising birefringent material and give some new insights for designing high‐performance optical materials based on the linear units with high polarizability anisotropy.