Brightly Luminescent Colloidal Silicon and Silicon-Carbide Quantum Dots from Liquid Precursors

Semiconductor nanocrystals (NCs) are of interest for a range of applications, some of which are best served by nontoxic indirect-bandgap materials like silicon carbide (SiC) and silicon (Si). However, in contrast to Si, true bandgap photoluminescence (PL) from SiC NCs has never been observed, with the reported PL reflecting impurities. We provide a brief overview of our current and recent work synthesizing brightly luminescent colloidal Si and SiC quantum dots from liquid precursors. Size-tunable core PL spanning the near-infrared to the red is indeed realized for Si NCs, with peak quantum yields (QYs) of around 70 % near peak emission wavelengths of 850 nm. For luminescent SiC NCs, on the other hand, the nature of both the particle and the PL is quite different, with passivated 2D-layered SiC NCs giving either narrow blue emission (425 nm peak PL with up to 70 % QY) or broad blue-green emission, depending on processing conditions, where both effects are linked to oxygen impurities. Density-gradient ultracentrifugation of colloidal 2D-layered SiC NCs in organic solvents reveals the modulation of impurity emission by transverse quantum confinement, and the implications of the difference in PL mechanism between Si and SiC will be discussed.