Colloidal synthesis and photophysical characterization of silicon-compatible Ge1−xSnx alloy quantum dots with composition-tunable near-infrared absorption and photoluminescence is reported.

Using hybrid functional calculations and experimental characterization, we analyze optical properties of 2–3 nm Ge1–x Sn x alloy quantum dots, synthesized by colloidal chemistry methods. Hybrid functional theory, tuned to yield experimental bulk band structure of germanium, reproduces directly measured properties of Ge1–x Sn x quantum dots, such as lattice constants, energy gaps, and absorption spectra. Time-dependent hybrid functional calculations yield optical absorption in good agreement with experiments, and allow probing the nature of the dark excitons in quantum dots. Calculations suggest a spin-forbidden dark exciton ground state, which is supported by the changes in the photoluminescence lifetimes with temperature and tin concentrations. The synthesis and theoretical understanding of Ge1–x Sn x alloy quantum dots will add to the overall toolbox of low to nontoxic, silicon-compatible group IV semiconductors with potential application in visible to near-infrared optoelectronics.

The colloidal synthesis of lithium silicate nanocrystals with varying morphology, composition, crystal structures, and high intensity visible luminescence is reported.