Constructing ultraviolet nonlinear optical crystals with large second harmonic generation and short absorption edges by using polar tetrahedral S2O3 groups

Abstract

It is generally considered difficult for traditional sulfates to exhibit strong second harmonic generation (SHG) responses and large birefringence values because SO₄ groups are nonpolar tetrahedral structures. However, by theoretical calculations, we found that polar tetrahedral S₂O₃ shows great improvements in anisotropy and second order polarizability compared to SO₄ while the wide band gap can be preserved. On this basis, a nonlinear optical (NLO) crystal (NH₄)₂S₂O₃ with excellent performance was synthesized. As expected, it exhibited a strong SHG response (3.3× that of KDP), suitable birefringence (0.077@546 nm) and a short absorption edge (238 nm). According to the first principles calculations, the polar tetrahedral S₂O₃ group is the main source for the SHG response of (NH₄)₂S₂O₃. These findings indicate that the polar S₂O₃ group is a kind of NLO functional group with superior comprehensive properties, and has great potential to develop more NLO crystals with superior comprehensive properties.