First-principles study lone-pair effects of Sb (III)-S chromophore influence on SHG response in quaternary potassium containing silver antimony sulfides

Abstract

First-principles studies of the geometric structures, electronic structures and optical properties of non-centrosymmetrical (NCS) KAg2SbS4, K2AgSbS4 and K2Ag3Sb3S7 and centrosymmetrical (CS) KAg2SbS3 and K3Ag9Sb4S12 have been performed by means of density functional theory. It is indicated that although they have similarity in their anionic groups and, the electronic structures, prominent features of the optical anisotropy or second-order nonlinear optical (NLO) susceptibilities are apparently different. The calculated birefringences are 0.0537, 0.0343, 0.1324, 0.2217 and 0.0604 which are attributed to the different anionic groups [SbS3] and triangles [AgS3]. Also, the calculated NLO responses are about 0.5×, 1.0× and 2.0× times than that commercial AgGaS2 (AGS, d36=11pm/V) for K2AgSbS4, KAg2SbS4 and K2Ag3Sb3S7, respectively. In comparison with the absolute magnitude of second harmonic generation (SHG) coefficients, the order K2Ag3Sb3S7>KAg2SbS4>K2AgSbS4 is clearly established in the SHG response. Further analysis based on the real-space atom-cutting method reveals that the main sources of the SHG properties of these compounds are from the Sb-S group, especially K2Ag3Sb3S7 is mainly attributed to the lone pair stereochemical activity of Sb (III)-S group.