Sr 2 Pb(BeB 5 O 10 )(BO 3 ): 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, Sr ₂ Pb(BeB ₅ O ₁₀ )(BO ₃ ) (SPBBO), is successfully designed and synthesized by chemical and crystalline modification of the perovskite-like K ₃ B ₆ O ₁₀ Cl NLO crystal. SPBBO displays a 3D BeB ₅ O ₁₀ ^3- open-framework structure composed of interconnecting BeB ₅ O ₁₃ groups with filled cationic Sr/Pb and anionic BO ₃ 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 BO ₃ result in the synergistic conjugation of Pb with host BeB ₅ O ₁₀ ^3- and filled BO ₃ 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.