OPTICAL PROPERTIES OF Ag7SiS5I AND Ag7GeS5I SINGLE CRYSTALS

Compounds with a disordered structure attract significant scientific interest, since structural disorder directly affects the properties of the material. This paper presents a study of the optical properties of Ag7SiS5I and Ag7GeS5I single crystal, which are related to compounds with the structure of argyrodite. Single crystals of quaternary Ag7SiS5I and Ag7GeS5I were grown by the method of directed crystallization from the melt. Investigation of grown single crystals by the XRD method indicates that both compounds crystallize in SG F-43m. The optical properties were studied at room temperature (20°C) in the spectral range of 200–1100 nm. The beginning of the optical transmission region is observed at λ = 790 nm and λ = 860 nm for Ag7SiS5I to Ag7GeS5I, respectively. It was established that Ag7GeS5I single crystals have a higher bandwidth compared to Ag7SiS5I. When transitioning from Ag7SiS5I to Ag7GeS5I, a shift of the transmission region to a longer wavelength region is observed. The energies of direct allowed and forbidden optical transitions in Ag7SiS5I and Ag7GeS5I single crystals were determined using the Tauc equation. It was established that the corresponding energies values are higher in the case of the Ag7SiS5I single crystal for both considered optical transitions. Keywords: argyrodites; single crystals; optical spectroscopy; optical transitions.