Rb₃Na(H₂C₃N₃O₃)₄·3H₂O with Large Birefringence

A mixed alkali-metal nonlinear optical (NLO) dihydro-cyanurate crystal Rb₃Na­(H₂C₃N₃O₃)₄·3H₂O has been synthesized via the hydrothermal method. Its calculated birefringence is about 0.368, which is very large, its ultraviolet (UV) cutoff edge is down to 230 nm, and the powder second harmonic generation (SHG) intensity is about 0.2 × KDP. In addition, a first-principles investigation of the electronic properties on Rb₃Na­(H₂C₃N₃O₃)₄·3H₂O was carried out. The calculated band gap and SHG coefficient values agree well with the experimental ones. These results suggest that it could be applied as a UV birefringent material.