A Congruent-Melt Infrared Nonlinear Optical Crystal Na₄SrAs₂S₈

Abstract

A quaternary metal thioarsenate infrared (IR) nonlinear optical (NLO) compound Na 4 SrAs 2 S 8 was successfully prepared by a high-temperature reaction method from stoichiometric agents. It crystallizes in the tetragonal P4n2 with the unit cell parameters a = 10.0393(3) Å, c = 6.9638(3) Å, and Z = 2, with the basic structural groups of isolated AsS 4 tetrahedra. Compared with benchmark IR NLO crystal AgGaS 2 (AGS), the title compound exhibits balanced optical properties of large band gap (3.05 eV vs. 2.60 eV) and considerable second harmonic generation response (0.95 × AGS). Moreover, the combined powder X-ray diffraction and differential scanning calorimetry analyses demonstrate that Na 4 SrAs 2 S 8 is a congruent-melting compound with a low melting point of 668 °C, which is benefical for bulk single crystal growth. Experimental and theoretical calculation results indicate that Na 4 SrAs 2 S 8 is a practically usable IR NLO crystal, also motivating the exploration of thioarsenates as high-performance IR NLO candidates.