The discovery of short-wave ultraviolet (SWUV, λ_PM < 266 nm, PM = phase-matching) and deep ultraviolet (DUV, λ_PM < 200 nm) nonlinear optical (NLO) crystals is urgently required and full of challenges. Unlike the conventional strategy of using π-conjugated groups (such as BO₃) as core motifs for constructing UV NLO crystals, herein the long-neglected stereochemically active lone pair (SCALP) groups ClO₃ and BrO₃ are innovatively proposed to be good UV NLO functional motifs based on the group property prediction, and the NLO performance of chlorates and bromates has been investigated systematically for the first time by first-principles methods. Benefiting from the high polarizability of ClO₃ and BrO₃ and their favorable alignments, the halate crystals AClO₃ and ABrO₃ (A = NH₄, K, Rb and Cs) exhibit high SHG coefficients comparable to that of classical β-BaB₂O₄ (4.2–4.8 × KDP for AClO₃ and 6.1–7.1 × KDP for ABrO₃). Meanwhile, their wide band gaps and large optical anisotropy lead to very short λ_PM deep into DUV and SWUV (185–195 nm for AClO₃ and 210–220 nm for ABrO₃). Remarkably, ABrO₃ shows a rare full-wavelength phase-matching capability. Hence AClO₃ and ABrO₃ could be promising DUV and SWUV NLO candidates, respectively, and the UV NLO potential of ClO₃ and BrO₃ is further demonstrated by profound mechanism analysis. This work opens up a new avenue for the development of SWUV and even DUV NLO materials.

中文翻译：

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在氯酸盐和溴酸盐中发现具有高立体化学活性孤电子对的优异紫外非线性光学材料

短波紫外（SWUV，λ _PM < 266 nm，PM = 相位匹配）和深紫外（DUV，λ _PM < 200 nm）非线性光学（NLO）晶体的发现是迫切需要且充满挑战的。与使用π共轭基团（例如BO ₃）作为构建UV NLO晶体的核心基序的传统策略不同，本文创新性地提出长期被忽视的立体化学活性孤对（SCALP）基团ClO ₃和BrO ₃是良好的UV NLO晶体。基于基团性质预测的NLO功能基序，以及氯酸盐和溴酸盐的NLO性能首次通过第一性原理方法进行系统研究。得益于ClO ₃和BrO ₃的高极化性及其有利的排列，卤酸盐晶体AClO ₃和ABrO ₃ (A = NH _{4 、K、Rb和Cs)表现出与经典β-BaB 2} O相当的高SHG系数₄（AClO _{3为 4.2–4.8 × KDP，ABrO 3}为 6.1–7.1 × KDP ）。同时，它们的宽带隙和大的光学各向异性导致深紫外和短紫外的λ _{PM非常短（AClO 3为185-195 nm，ABrO 3}为210-220 nm ）。值得注意的是，ABrO ₃显示出罕见的全波长相位匹配能力。因此，AClO ₃和ABrO ₃可能分别是有前途的DUV和SWUV NLO候选者，并且通过深入的机理分析进一步证明了ClO ₃和BrO ₃的UV NLO潜力。这项工作为SWUV甚至DUV NLO材料的开发开辟了一条新途径。