CaB5O7F3: A Beryllium-Free Alkaline-Earth Fluorooxoborate Exhibiting Excellent Nonlinear Optical Performances

Noncentrosymmetric (NCS) fluorooxoborates are one of the most attractive systems for discovering the new deep-ultraviolet (DUV) nonlinear optical (NLO) materials. Here, we report the formation, crystal structure, and optical properties of a new NCS alkaline earth fluorooxoborate: CaB₅O₇F₃. It exhibits excellent NLO performances including large band gap (8.75 eV), large second harmonic generation intensity (2 × KH₂PO₄ and 0.4 × β-BaB₂O₄, under 1064 and 532 nm radiation, respectively), and moderate birefringence (0.07 @ 1064 nm) that enables frequency doubling down to 183 nm. It demonstrates that CaB₅O₇F₃ is a promising DUV NLO material.