Rb(3)Na(H(2)C(3)N(3)O(3))(4)·3H(2)O with Large Birefringence

[Image: see text] A mixed alkali-metal nonlinear optical (NLO) dihydro-cyanurate crystal Rb(3)Na(H(2)C(3)N(3)O(3))(4)·3H(2)O 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 Rb(3)Na(H(2)C(3)N(3)O(3))(4)·3H(2)O 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.