The role of quantum confinement and surface chemistry in silicon nanocrystals at the strong confinement regime

Using infrared photo-induced absorption (PIA) spectroscopy, we have found a remarkable correlation between inter-sub-level (ISL) optical transitions and the photoluminescence (PL) from silicon nanocrystals. Our results indicate that the quantized electronic subleveis of the nanocrystals are resonantly coupled to surface vibrational modes via a polarization field produced by coherent longitudinal polar vibrations. The model and the experimental results support our findings that the mechanism responsible for the efficient PL from silicon nanocrystals should be assigned to inhibition of nonradiative channels rather than enhancement of radiative transitions.