Confocal microscopy and spectroscopy of defect photoluminescence in single SiO_2 nanoparticles

摘要

We present new results on single SiO_2 nanoparticles (SiO_2 NPs). NPs were obtained by full oxidation in water of silicon nanocrystals synthesized by CO_2 laser pyrolysis of SiH_4. Samples of SiO_2 NPs embedded in low concentration in a thin polymer layer were prepared by spin-coating a dedicated solution on quartz cover slides. Using focused higher order laser modes, we determine the three-dimensional orientation of the nanoparticles' transition dipole moment (TDM). The SiO_2 NPs were found to possess a quite stable and randomly oriented TDM. However, characteristic dynamical effects featuring single NPs such as fluorescence intermittency and TDM flipping could also be observed. Photoluminescence (PL) spectroscopy of single SiO_2 NPs revealed spectra with a double-peak structure consisting of a narrow zero-phonon line and a broader phonon band. The phonon band can be attributed to longitudinal optical phonons excited in the SiO_2 network.