Uncovering the Structural Diversity and Excellent Performance of a Deep Ultraviolet Nonlinear Optical System Li(B₂O₃)_nF (n= 1, 1.5, 2, and 3) by Multicomponent Prediction

Design of nonlinear optical (NLO) materials with the second harmonic generation (SHG) phase-matching (PM) ability reaching the deep ultraviolet (deep-UV, ≤200 nm) region is urgently needed owing to their vital role in solid-state lasers. Herein, we proposed a structural diversity-inducing performance regulation strategy for exploring novel deep-UV NLO fluorooxoborates. The dynamically and thermodynamically stable fluorooxoborates were discovered in the Li(B2O3)nF (n = 1, 1.5, 2, and 3) system by using the global evolutionary algorithm. It is found that the anionic units in the Li(B2O3)nF (n = 1, 1.5, 2, and 3) system favor a two-dimensional anionic framework, and a series of novel B-O-F functional layers with different [BO3]:[BO3F] ratios and spatially layer-bulkling were discovered. Predicted non-centrosymmetric structures at or near the ground states exhibit large band gaps (6.53–7.50 eV) and large birefringences (0.0714–0.1253 at 1064 nm), and LiB2O3F (I–III and V), LiB4O6F (I, II, and IV–VI), and LiB6O9F-II have large NLO coefficients (1.0–3.6 × KDP). Especially, LiB2O3F (I–III and V), LiB4O6F (I–VI), and LiB6O9F-II have deep-UV SHG PM wavelengths, of which LiB2O3F (I–III) even have potential in the sixth harmonic light output of 1064 nm laser. These findings demonstrate that the ratio adjustment of a π-conjugated unit and fluorine-based unit and the modulated layer flatness facilitate deep-UV SHG PM capacity.