Photoluminescence and electronic structure of α'-Ag8GeS6 crystals

Abstract

The Ag8GeS6 crystal was synthesized by the direct melting of the elementary Ag, Ge, and S high-purity grade stoichiometric mixture in a sealed quartz ampoule. This argyrodite crystallizes in orthorhombic structure [Pna21 space group (No. 33)] below ≈483 K. The theoretical first-principle calculations of the electronic band structure and density of states of an α'-Ag8GeS6 crystal are estimated by the generalized gradient approximation. The Perdew–Burke–Ernzerhof functional was utilized. All of the calculated parameters correlate well with the known experimental data. Based on the electronic band structure, the effective mass of the electrons and holes was calculated. The anisotropic behavior of electronic band structure is discussed. Temperature and carrier concentration dependence of the Seebeck coefficient is calculated. The temperature behavior of α'-Ag8GeS6 photoluminescence spectra is presented. The emission spectra are studied in the temperature range between 17 and 130 K and laser power excitation between 4 and 512 mW and in the spectral range of 750–1650 nm. Two main emission bands at ≈1.35 and ≈1.57 eV are observed and discussed.