Li8NaRb3(SO4)6·2H2O as a new sulfate deep-ultraviolet nonlinear optical material

Abstract

Sulfates have long been ignored as nonlinear optical materials over the past decades. Here we report a new sulfate deep-ultraviolet nonlinear optical material Li₈NaRb₃(SO₄)₆·2H₂O synthesized by the facile water solution method. It crystallizes in the asymmetric monoclinic space group C2 (No. 5). Its single-crystal structure features a three-dimensional framework made up of SO₄ and LiO₄ tetrahedra. Powder second-harmonic generation tests demonstrate that Li₈NaRb₃(SO₄)₆·2H₂O is phase-matchable with a second-harmonic generation response of about 0.5 × KH₂PO₄. Ultraviolet-visible-near-infrared diffuse reflectance spectra illustrate that the ultraviolet cutoff edge of Li₈NaRb₃(SO₄)₆·2H₂O may be as low as λ < 190 nm. Theoretical calculations reveal that the optical properties of Li₈NaRb₃(SO₄)₆·2H₂O are mainly attributed to S–O groups. All these results reveal that Li₈NaRb₃(SO₄)₆·2H₂O may possess potential use in the deep-ultraviolet nonlinear optics field. We believe that the discoveries in our work will attract scientists’ attention to sulfate systems for their potential as deep-ultraviolet nonlinear optical materials.