Insights into electronic and optical properties of AGdS2 (A = Li, Na, K, Rb and Cs) ternary gadolinium sulfides

Abstract The ternary rare-earth sulfides ALnS2 have been widely applied in phosphors or scintillator materials. This study focused on systematically discussing the structural, electronic and optical properties of AGdS2 (A = Li, Na, K, Rb and Cs) ternary gadolinium sulfides using First-principles calculations for a better understanding of the physical properties of AGdS2. The ΔH values of all these sulfides reveal that they are phase stable, and LiGdS2 has the best phase stability. Electronic properties, including band structure, DOS, electron density difference and Mulliken population, provide that these sulfides are indirect band-gap semiconductors and have strong Gd–S covalent bonds and weak A-S ionic-covalent mixed bonds. The calculated absorption coefficients and reflectivity indicate that these AGdS2 sulfides are appropriate for the longer wavelength lasers. The anisotropy in optical properties for AGdS2 sulfides was studied through the polycrystalline and directional static dielectric constants e1(0) and static refractive indexes n(0), and the order of optical anisotropy can be obtained as LiGdS2 > NaGdS2 > KGdS2 > RbGdS2 > CsGdS2.