In the quest for organic–inorganic metal halides (OIMHs) that harmoniously combine large second harmonic generation (SHG) efficiency with broad bandgaps, our study introduces a series of noncentrosymmetric and polar piperazine zinc halides, (C₄H₁₁N₂)ZnX₃ (X = Cl, Br, I). The distinct influence of halide anion size on the configuration of ZnNX₃ tetrahedra is uncovered, revealing a design principle for enhancing SHG activity and manipulating bandgap characteristics. Specifically, (C₄H₁₁N₂)ZnCl₃ is the first example of deep-ultraviolet (deep-UV) nonlinear optical (NLO) OIMHs, with UV transparency lower than 190 nm and moderate SHG effect, 0.8 times KH₂PO₄ (KDP). Meanwhile, compared with (C₄H₁₁N₂)ZnI₃ (2.1 times KDP, 4.52 eV), (C₄H₁₁N₂)ZnBr₃ boasts a widened bandgap of 5.53 eV while maintaining a striking SHG response (2.5 times KDP), representing a pinnacle in the SHG-bandgap balance among OIMHs with E_g exceeding 5.0 eV. Computational analyses underscore the critical roles of halide orbitals and ZnNX₃ distortions in dictating SHG efficiency, with increasing halide polarizability correlating with heightened SHG contributions. This study paves the way for a novel approach to designing short-UV NLO crystals based on OIMHs.

中文翻译：

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(C4H11N2)ZnX3 (X = Cl、Br、I) 中卤化物驱动的极性调谐和优化的 SHG 带隙平衡


在寻找将二次谐波产生（SHG）效率与宽带隙和谐结合的有机-无机金属卤化物（OIMH）时，我们的研究引入了一系列非中心对称和极性哌嗪锌卤化物，（C ₄ H ₁₁ N ₂ )ZnX ₃ (X = Cl、Br、I)。揭示了卤化物阴离子尺寸对 ZnNX ₃ 四面体构型的明显影响，揭示了增强 SHG 活性和操纵带隙特性的设计原理。具体来说，(C ₄ H ₁₁ N ₂ )ZnCl ₃ 是深紫外（深紫外）非线性的第一个例子光学（NLO）OIMH，紫外透明度低于190 nm，具有中等SHG效应，是KH ₂ PO ₄ (KDP)的0.8倍。同时，与(C ₄ H ₁₁ N ₂ )ZnI ₃ (2.1倍KDP，4.52 eV)相比，(C < b15> H ₁₁ N ₂ )ZnBr ₃ 拥有 5.53 eV 的加宽带隙，同时保持惊人的 SHG 响应（2.5 倍 KDP），代表 OIMH 中 SHG 带隙平衡的顶峰，E _g 超过 5.0 eV。计算分析强调了卤化物轨道和 ZnNX ₃ 畸变在决定 SHG 效率中的关键作用，卤化物极化率的增加与 SHG 贡献的增加相关。这项研究为基于 OIMH 设计短紫外 NLO 晶体的新方法铺平了道路。