Energy Transfer Between Molecules in the Vicinity of Metal Nanoparticle

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Bobbara, Sanyasi Rao
Nanoplasmonics , Fluorescence Anisotropy , Non-Radiative Energy Transfer
Nanoplasmonics has opened up the gates for numerous innovations. Recent studies showed that metal nanoparticles, when introduced into the solar cells and organic light emitting diodes, would greatly enhance their efficiencies. Though these advances are promising, they require a tool for investigating the interactions occuring at the microscopic level to further optimize their performance. In that context, we are interested in understanding the energy transfer mechanism between molecules in the vicinity of metal nanoparticle. Time-resolved fluorescence intensity and anisotropy experiments on single and clusters of Silver-Silica core-shell nanoparticles coated with Rhodamine B(RB) dye molecules, (Ag-SiO2-RB) were performed. We witnessed the signature of the interaction between RB molecules and metal nanoclusters in the form of the enhanced fluorescence intensity decay rates. The fluorescence lifetime of RB in the vicinity of the nanoparticles was (600 +/- 100) ps, as compared to (2.4+/-0.3)ns in the absence of nanoparticle. While the anisotropy of RB molecules in the absence of nanoparticle has remained almost constant(0.075+/-0.029) over long times; anisotropy in the presence of particles showed wide range of values immediately after excitation. Surprisingly high anisotropy values, at about 10 ns after excitation, were observed with a mean of about (0.145+/-0.025). We interpret the high and low initial anisotropies of the clusters, relative to the case of RB alone, to be due to the interaction of dye molecules with collective plasmon modes of the clusters.
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