The fluorescence of semiconductor nanoparticles is greatly influenced by the interactions of close by plasmonic metal particles. If the fluorescence energy of the semiconductor nanoparticles is in resonance with the plasmonic frequency of the metal, the radiative and non-radiative rate can be enhanced. Here, the distance between the metal- and semiconductor nanoparticles as well as the geometry of the system has a huge influence on the fluorescence behavior of the whole system. For example, a direct contact of the two components leads to complete fluorescence quenching whereas a certain distance between the two can even lead to fluorescence enhancement.

Here we present a wet-chemical approach to control the distance between plasmonic metals and type-I & II (CdSe/CdS or ZnSe/CdS) semiconductor dot-in-rod (DR) structures. Using a silica shell around the DRs as a dielectric spacer we can investigate the effect of attached plasmonic metals (Ag & Au) on the fluorescence behavior of the DRs. The application of different sources of silica (e.g. TMOS, TEOS, TPOS) enables us to finely tune the thickness of the shell on the nanometer scale down to 8 nm. Different geometries of the attached metal nanoparticles (e.g. spherical nanoparticles or nanorods) allow tuning of the spectral overlap as well as the spatial electric field distribution generated through the surface plasmon resonances, giving the opportunity to influence the fluorescence behavior of the system specifically. Some geometries can lead to strong electric fields near to the DRs. For instance, rod shaped metal particles show high fields at the tips whereas spherical particles show a homogeneous field distribution. Depending on the type of metal attached to the silica coated DRs diverse effects can be observed. In general, the addition of gold enhances the emission probability and will lead to a fluorescence enhancement (as used for SERS). This effect is highly dependent on the distance, amount and arrangement of the metal particles around the DRs. The addition of silver leads to an enhanced emission due to an increased absorption rate in the regime of the plasmon resonance. In our spectral studies, which we perform at low and room temperature, we observe a stabilization in blinking behavior of individual hybrids and a drastic drop of their fluorescence lifetimes.