Zn₃B₇O₁₃Cl: A New Deep-Ultraviolet Transparency Nonlinear Optical Crystal with Boracite Structure

Nonlinear optical crystals play important roles in modern laser science and technology. However, the design and growth of new nonlinear optical (NLO) materials is still a challenging issue for researchers. Due to the excellent performance of Mg₃B₇O₁₃Cl crystal, we paid attention to the optimization of its structure, in order to find new NLO materials with favorable properties. Here, Zn₃B₇O₁₃Cl crystals were obtained by a high-temperature solution method. Its structure was determined to be the trigonal symmetry with a polar space group of R3c, which is more highly symmetric than that of Mg₃B₇O₁₃Cl (Pca2₁). The experimental and theoretical investigations demonstrated that the title compound exhibits a short absorption cutoff (band gap ∼6.53 eV), moderate SHG responses (2.2 times that of KDP at 1064 nm), and the improved birefringence, which results from the large distortion and anisotropy of borate groups and zinc polyhedrons. Therefore, the structural modification of Mg₃B₇O₁₃Cl by zinc cations achieves a balance between the deep-ultraviolet transparency, the nonlinear optical effect, and the moderate birefringence, which is very significant for the design of practical NLO materials.