Dynamical effects of defect photoluminescence from single SiO2 and Si nanoparticles

We present results of photoluminescence (PL) studies of single SiO2 nanoparticles (SiO2 NPs) and single Si nanocrystals (Si NCs). Single particle spectroscopy reveals almost identical PL spectra for both kinds of nanosized systems. The emission curves exhibit a zero-phonon line and one or two phonon bands, which can be assigned to longitudinal optical phonons in SiO2. Using cylindrical vector beams for imaging the fluorescence of single particles we show that they possess a linear excitation transition dipole moment (TDM). Furthermore, the single particle fluorescence patterns demonstrate upon continuous excitation dynamical effects such as blinking, bleaching, and flipping of the TDM. The latter is related to a redistribution of defect states caused by charge fluctuations in the surrounding of the embedded NP. Excitation fluorescence images visualize the intermediate state resulting from the TDM flipping. (C) 2011 Published by Elsevier B. V.