Silicon nanocrystals were synthesized by CO(2) laser pyrolysis of SiH(4). The fresh silicon nanopowder was oxidized in water to obtain SiO(2) nanoparticles (NPs) exhibiting strong red-orange photoluminescence. 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 an argon ion laser at 488 nm with higher-order laser modes (azimuthally and radially polarized doughnut modes) for excitation, the three-dimensional orientation of the nanoparticles' transition dipole moment was investigated in a confocal microscope. The linear transition dipole moment was found to be rather stable and randomly oriented. However, dynamical effects such as fluorescence intermittency and transition dipole moment flipping could also be observed. The spectral analysis of single SiO(2) NPs revealed double-peak spectra consisting of a narrow zero-phonon line and a broader phonon band being associated with the excitation of longitudinal optical phonons in the SiO(2) NP.

We present experimental and theoretical results on changing the fluorescence emission spectrum of a single molecule by embedding it within a tunable planar microcavity with subwavelength spacing. The cavity length is changed with nanometer precision by using a piezoelectric actuator. By varying its length, the local mode structure of the electromagnetic field is changed together with the radiative coupling of the emitting molecule to the field. Because mode structure and coupling are both frequency dependent, this leads to a renormalization of the emission spectrum of the molecule. We develop a theoretical model for these spectral changes and find excellent agreement between theoretical prediction and experimental results.

We evaluate the field distribution in the focal spot of the fundamental Gaussian beam as well as radially and azimuthally polarized doughnut beams focused inside a planar metallic sub-wavelength microcavity using a high numerical aperture objective lens. We show that focusing in the cavity results in a much tighter focal spot in longitudinal direction compared to free space and in spatial discrimination between longitudinal and in-plane field components. In order to verify the modeling results we experimentally monitor excitation patterns of fluorescence beads inside the lambda/2-cavity and find them in full agreement to the modeling predictions. We discuss the implications of the results for cavity assisted single molecular spectroscopy and intra-cavity single molecular imaging.