Strategies for designing two-dimensional nonlinear optical layers from KBBF and BBO crystals†
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.