A Potential UV Nonlinear-Optical Crystal with Strong Second-Harmonic Response: RbNa2Eu2(BO3)3

Abstract

Ultraviolet (UV) nonlinear optical (NLO) crystals with second-harmonic generation (SHG) response can efficiently output UV coherent light, which has important applications in UV solid-state lasers. Herein, we designed and synthesized a novel Eu-based borate (NLO) crystal, RbNa2Eu2(BO3)3 (RNEBO), which introduces Eu to A3RE2(BO3)3 (A = alkali metal, RE = rare earth) system applied in the UV direction firstly and exhibits both strong SHG activity and widely optical transmission window. The RNEBO crystallizes into the non-centrosymmetric (NCS) space group Amm2, featuring a three-dimensional framework of [EuBO3]∞ layers with isolated [BO3]3- groups bridging in a coplanar arrangement. Meanwhile, the alkali metal cations Rb+ and Na+ were incorporated into the void of the anion framework to ensure coordination and charge balance. The distinctive internal structure endows RNEBO to possess large SHG response (~3.55 × KDP) and UV transmittance of 6.17% at 200nm. This finding confirms that RNEBO is a potentially UV NLO crystals and provides valuable insights for the exploration of Eu-based borate UV NLO crystals in the future.