K5Mg2La3(BO3)6: An Efficient, Deep-Ultraviolet Nonlinear Optical Material

KBe2BO3F2 (KBBF) is the sole nonlinear optical (NLO) crystal that can practically generate deep-ultraviolet (UV) coherent light by a direct second-harmonic generation (SHG) process. However, the toxic BeO and crystal layer habit limit its application. With this background, a new beryllium-free borate, K5Mg2La3(BO3)6 (KMLBO), has been designed and synthesized through a high-temperature solution method. KMLBO crystallizes into the noncentrosymmetric space group P31m (No. 157) and features a three-dimensional framework structure consisting of alveolate [LaBO3]∞ layers further tightly bound via interlayer [BO3]3– groups. KMLBO not only exhibits desirable performances including deep-UV transparency, large SHG (∼3.1 × KH2PO4), and phase-matchability but also overcomes the crystal layer habit of KBBF, demonstrating that it is a potential deep-UV NLO crystal.