Two-dimensional (2D) nonlinear optical (NLO) monolayers are brilliant candidates for future nanoscale laser devices, typically within the ultra-violet (UV) range. While for bulk crystals, KBe₂BO₃F₂ (KBBF) and β-BaB₂O₄ (BBO) are the two NLO crystals most applied in the UV region. In this article, we designed a series of 2D-KBBF and 2D-BBO monolayer families, which were predicted by first-principles calculations to be transparent in the deep ultra-violet (DUV) to visible (vis) range. And their NLO effects are also enhanced compared to the bulk. Both 2D-BBO and 2D-KBBF preserve the planar triangular borate ion structures.

中文翻译：

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由KBBF和BBO晶体设计二维非线性光学层的策略

二维（2D）非线性光学（NLO）单层是未来纳米级激光设备（通常在紫外线（UV）范围内）的绝佳候选者。而对于块状晶体，KBE ₂ BO ₃ ˚F ₂（KBBF）和β-BAB ₂ ø ₄（BBO）是两个NLO晶体在UV区域最适用。在本文中，我们设计了一系列2D-KBBF和2D-BBO单分子层系列，它们通过第一原理计算预测在深紫外（DUV）到可见（vis）范围内是透明的。与批量相比，它们的NLO效果也得到了增强。2D-BBO和2D-KBBF都保留了平面三角形硼酸根离子结构。