Comparing the influence of gold nanorods and -discs on the spontaneous decay rate of Eu-chelate dye

Nanometre-sized metal structures support localized surface plasmons associated with the collective oscillations of conduction band electrons. These modes can give rise to a drastic enhancement of local electromagnetic fields close to the surface of the structures. As a consequence, the fluorescence properties of molecules in that near field zone become strongly modified. In this paper, we investigate the modifications of the de-excitation processes in Eu-chelate dye for various nanoparticle sizes and shapes. By this coupling, in the electronic de-excitation process the corresponding radiative and non-radiative rates can be enhanced by orders of magnitude with respect to the free-space case. When the plasmon resonance overlaps well with the molecule's fluorescence emission frequency the interacting molecules show a dramatically shortened fluorescence lifetime but an enhanced signal amplitude. This is a valuable mechanism for new labelling techniques in biosciences and for modifications of OLED emission properties.