Blue photoluminescence from ultrasmall silicon nanocrystals produced by nanosecond pulsed laser ablation in toluene

A report on strong and fast blue photoluminescence (PL) from silicon nanocrystals (Si-ncs) suspended in toluene solution is presented. They were fabricated through nanosecond pulsed laser ablation of the silicon target in toluene. Transmission electron microscopy observations confirm that the Si-ncs are well dispersed and the most of them are smaller than 2 nm. Fourier transform infrared spectra indicate that the surface of the Si-ncs is passivated by some groups from toluene. The detailed study of PL spectra and PL excitation spectra reveals that the photoexcited carriers not only are present in the quantum confined Si-ncs cores but also occur at the Si-ncs surface, and the resonant electron transfer from the surface bonding states to the conduction band of quantum confined Si-ncs can efficiently occur. Time-resolved PL spectrum exhibits a triple-exponential PL decay with lifetimes of 0.73, 3.8 and 13.5 ns, and implies that the optical recombinations and the resonant electron transfer are both very rapid and of the order of nanoseconds.