Calculations Of IR Materials In Ag-containing Quaternary-chalcogenides

The mid-far-infrared?MFIR?lasers have important applications for civil and military region.As it is known,metal chalcogenides with excellent properties including high laser damage thresholds?LDTs?,large second harmonic generation?SHG?response and better optical transparency for candidates of promising IR materials.At present,an important factor in the application of IR nonlinear optical?NLO?materials is that it is difficult to achieve a balance between LDTs and NLO coefficient.To obtain excellent IR NLO materials with good balance between LDTs and SHG response,some new IR NLO materials with potential applications have been constantly reported by experimental or theoretical method.This paper aiming at guiding exploration novel IR NLO material and with alkali metal Ag-containing quaternary-chalcogenide compounds as the research system.Their electronic structure and optical properties were calculated via density functional theory?DFT?method.The study will have a theoretical guidance for experimental exploration.Two alkali metal Ag-containing quaternary-chalcogenide compounds KAg₂TS₄?T = P,Sb?has been studied by means of first principles,electronic density difference and bond population.It is obviously found that KAg₂PS₄ possess relatively wide band gap and large birefringence owing to the strongly covalent interaction behavior of P-S bond than Sb-S.First-principles studies of five thioantimonates KAg₂SbS₄,K2AgSbS₄,K2Ag3Sb3S7,KAg₂SbS3 and K3Ag9Sb4S12 have been performed by means of DFT.It is obvious that three latter thioantimonates with Sb?III?have relatively large birefringence may be due to [AgS3] and [SbS3] groups.For first three noncentrosymmetrical?NCS?compounds,we reveal that the main sources of the SHG properties of these compounds is from the Sb-S group by the real space atom cutting method,especially K2Ag3Sb3S7 is mainly attributed to the lone pair stereochemical activity of Sb?III?-S group to enhance SHG properties.The study can provide an idea in synthesizing large SHG response in this system.