Electronic and optical properties of GeS and GeS:Gd

In this paper, the results of the first principles calculations within the framework of the density functional theory of the electronic spectrum of a GeS crystal are presented. The density of states and interband optical transitions are investigated. It was found that GeS compounds have semiconducting properties with a bandgap of 1.52 eV. The main contribution of the bands in the vicinity of the Fermi level is from the 3[Formula: see text] and 3[Formula: see text] states of the S and Ge atoms, respectively. The highest amplitude, about 2.3 eV ([Formula: see text], is mainly associated with the interband optical transitions between the states [Formula: see text]. The results of the luminescence studies of GeS and GeS:Gd layered crystals at room-temperature are presented. A noticeable increase in the intensity of the luminescence radiation in GeS:Gd has been established. The reason for the increase in the effectiveness of photoluminescence is due to the overlapping of optical transitions of GeS at 695 nm wavelength with the radiation lines of Gd[Formula: see text]ion at that same energy.