Two-Dimensional Deep-Ultraviolet Beryllium-Free KBe₂BO₃F₂ Family Nonlinear-Optical Monolayer

A two-dimensional (2D) nonlinear-optical (NLO) material could generate a breakthrough in the development of a nanoscale laser, especially in the range of high-energy and short-wavelength deep ultraviolet (DUV; <200 nm). KBe₂BO₃F₂ (KBBF) is the only bulk crystal actually used in the DUV region. In this letter, we designed the new 2D KBBF family monolayer Al₃LiB₂O₆F₄ (2D-ALBF), which was predicted to have a broad DUV-vis transparent range and an enhanced NLO effect that doubles the frequency. 2D-ALBF keeps the infinite planar [Be₂BO₃F₂]_∞ structure in KBBF but does not contain the toxic beryllium element.