Sr2Pb(BeB5O10)(BO3): An Excellent Ultraviolet Nonlinear-Optical Beryllium Borate by the Pb-Modified Construction of a Conjugated System and Lone-Pair Effect

The design of material by chemical and/or crystalline modification of a classic structure model benefits not only the optimized physical properties but also the controllability and efficiency. Herein, a new nonlinear-optical (NLO) beryllium borate crystal, Sr2Pb­(BeB5O10)­(BO3) (SPBBO), is successfully designed and synthesized by chemical and crystalline modification of the perovskite-like K3B6O10Cl NLO crystal. SPBBO displays a 3D BeB5O10 3– open-framework structure composed of interconnecting BeB5O13 groups with filled cationic Sr/Pb and anionic BO3 groups, which exhibits the striking enhancement of the second-harmonic-generation (SHG) response (8 × KDP) and birefringence (0.10) compared to the parent model. Replacement of K by Sr and Pb with a lone pair and replacement of Cl by conjugated BO3 result in the synergistic conjugation of Pb with host BeB5O10 3– and filled BO3 groups, contributing to the striking enhancement of the SHG and birefringence. Single-crystal measurements show that SPBBO has a short UV absorption edge of 280 nm with a wide energy band gap of 4.35 eV and an outstanding laser-induced resistant behavior with a remarkably high laser-induced damage threshold of 2100 MW cm–2. The excellent properties indicate that the SPBBO crystal is a very promising UV NLO functional material.