Abstract
In this paper, we study theoretically the electron and spectral properties of Ge1-xSnx systems, including alloys, cubic- and spherical quantum dots. The single-particle electron and hole states are calculated within the sp3d5s* tight-binding approach and used in further modeling of the optical properties. We systematically study the interplay of Sn-driven indirect-direct band-gap transition and the quantum confinement effect in systems of reduced dimensionality. We demonstrate the regime of sizes and composition, where the ground state in Ge1-xSnx quantum dot is optically active. Finally, we calculate absorbance spectra in experimentally-relevant colloidal quantum dots and demonstrate a satisfactory agreement with experimental data.