LiNaB₆O₉F₂: A Promising UV NLO Crystal Having Fluorine‐Directed Optimal Performances and Double Interpenetrating ³[B₆O₉F₂]_∞ Networks

Abstract A long‐lasting challenge in ultraviolet (UV) nonlinear optical (NLO) materials design is to combine conflicting and harsh properties into one structure, including wide UV transparency, strong NLO efficiency, and moderate birefringence to realize phase‐matching at short wavelength. A fluorine‐directed material design strategy is adopted to accelerate the process of finding NLO materials with optimal performances. In this work, taking LiB₃O₅ (LBO) as a maternal structure, one O atom with two F atoms is substituted and LiNaB₆O₉F₂ which possesses novel double interpenetrating ³[B₆O₉F₂]_∞ networks and fluorine‐directed optimal performances including enhanced birefringence and phase‐matching capacity is successfully obtained. The perfect balance among deep‐UV cutoff edge, large second‐harmonic generation (SHG) response (1.1 × KDP), and moderate birefringence (0.067 at 1064 nm) of LiNaB₆O₉F₂ makes it a promising UV NLO crystal.