Two noncentrosymmetric alkali metal phosphates MZnPO4 (M = Rb, Cs) with honeycomb-like structures

In recent years, phosphates have become a research hotspot to explore new ultraviolet (UV) nonlinear optical (NLO) materials. Herein, two NLO materials MZnPO 4 (M = Rb, Cs) are synthesized by cation substitution in alkali-zinc orthophosphates. Although they crystallize in different space groups P 2 1 and Imm 2, respectively, they both have a honeycomb-like topological structure consisting of corner-shared PO 4 and ZnO 4 tetrahedra and separated by "M" cations. Two compounds exhibit mild powder second harmonic generation (SHG) responses (1.2 and 0.5 × KDP for RbZnPO 4 and CsZnPO 4 , respectively) with type I phase matching behaviors and short absorption edges (226 nm for RbZnPO 4 and 231 nm for CsZnPO 4 ). Furthermore, their thermal properties , infrared (IR) spectra and theoretical calculations are also mentioned in the paper. The synthesis and structure-property relationship described in the system will enable discovery of new NLO materials.