Synthesis of Ligand-Stabilized Silicon Nanocrystals with Size-Dependent Photoluminescence Spanning Visible to Near-Infrared Wavelengths

We report a chemical route to colloidal silicon (Si) nanocrystals, or quantum dots, with widely tunable average diameter, from less than 3 nm up to 90 nm and peak photoluminescence (PL) from visible wavelengths to the bulk band gap of Si at 1100 nm. The synthesis relies on the high temperature (>1100 degrees C) decomposition of hydrogen silsesquioxane (HSQ) to obtain Si quantum dots with good crystallinity and a narrow size distribution with tunable size embedded in SiO2. The oxide matrix is removed by hydrofluoric acid etching in the dark. Subsequent thermal hydrosilylation with alkenes yields free, solvent-dispersible Si nanocrystals with bright PL. The relationship between PL energy and size, exhaustively characterized by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD), is reported.