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

Abstract

In recent years, phosphates have become a research hotspot to explore new ultraviolet (UV) nonlinear optical (NLO) materials. Herein, two NLO materials MZnPO4 (M = Rb, Cs) are synthesized by cation substitution in alkali-zinc orthophosphates. Although they crystallize in different space groups P21 and Imm2, respectively, they both have a honeycomb-like topological structure consisting of corner-shared PO4 and ZnO4 tetrahedra and separated by "M" cations. Two compounds exhibit mild powder second harmonic generation (SHG) responses (1.2 and 0.5 × KDP for RbZnPO4 and CsZnPO4, respectively) with type I phase matching behaviors and short absorption edges (226 nm for RbZnPO4 and 231 nm for CsZnPO4). 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.