SrZnSnSe$_4$: A quaternary selenide with large second harmonic generation and birefringence

Abstract

Infrared nonlinear optical (NLO) materials with great laser conversion efficient play a key role in military and civil fields. SrZnSnSe$_4$ was synthesized via replacing S elements with Se in SrZnSnS$_4$ compound. SrZnSnSe$_4$ crystallizes a two-dimensional layered structure with nearly parallel alignment of anionic groups [ZnSe$_4$] and [SnSe$_4$]. The experimental results show that the second harmonic generation (SHG) is about 5 times of AgGaS2, and the band gap of SrZnSnSe$_4$ is 1.82 eV by direct measured method. In combination with theoretical calculation, the SHG coefficients of SrZnSnSe$_4$ is d33 = 30.03 pm/V, and the birefringence is 0.290 at incident laser of 1240 nm, which can contribute to phase matching. These evidences show that SrZnSnSe$_4$ can balance well among band gap, frequency doubling effect and birefringence, therefore, it is an excellent candidate for infrared NLO materials.