Beryllium-Free KBBF Family of Nonlinear-Optical Crystals: AZn₂BO₃X₂ (A = Na, K, Rb; X = Cl, Br)

Abstract

A series of a novel beryllium-free KBBF family of nonlinear-optical materials AZn₂BO₃X₂ (A = K, Rb and X = Cl; A = Na, K, Rb and X = Br) were successfully synthesized through molecular engineering design, and single crystals of AZn₂BO₃Cl₂ (A = K, Rb) were grown by a spontaneous nucleation technique from self-flux systems. As a representative for the halogen KBBF family of crystals, KZn₂BO₃Cl₂ features the infinite lattice layer [Zn₂BO₃Cl₂]_∞ made up of BO₃ and ZnO₃Cl anionic groups, and the in-layer BO₃ groups are completely coplanar and well-aligned. Besides, KZn₂BO₃Cl₂ exhibits high transmittance in the range of 300-2000 nm with a UV-transmission cutoff of around 200 nm according to transmission spectra. The compounds of AZn₂BO₃Cl₂ (A = K, Rb) are both phase-matchable with powder second-harmonic-generation efficiencies of 1.3 and 1.17 times that of KH₂PO₄ for KZn₂BO₃Cl₂ and RbZn₂BO₃Cl₂, respectively, which are similar to that of KBBF.