Investigations on the Synthesis, Crystal Structure, Linear- and Nonlinear-Optical Properties of the Zinc Germanate Rb₂ZnGe₂O₆

Abstract

A quaternary nonlinear-optical (NLO) zinc germanate, Rb₂ZnGe₂O₆ (RZGO), was prepared from its stoichiometric melts, which belongs to the noncentrosymmetric space group <i>C</i>222₁ (No. 20) and features a 3D framework formed by GeO₄ tetrahedra, ZnO₄ tetrahedra, and Rb⁺ cations filling into the void space. RZGO displays a good phase-matchable second-harmonic-generation (SHG) intensity similar to that of KH₂PO₄. The UV cutoff edge for RZGO was found to be approximately 0.37 μm with a broad optical band gap of 3.22 eV, indicating a large laser-induced damage threshold. Further characterizations suggested that this compound displays an excellent thermal stability (1014 °C) and melts congruently. Besides, theoretical analysis was also implemented to investigate the electronic structures and effective NLO coefficients as well as the origin of the observed SHG response for RZGO. The present study can enrich the diversity of acentric germanate structures and pave the way for the synthesis of new NLO compounds.