Influence of whispering gallery modes (WGMs) on energy transfer

In single microcavities of diameter varying from 18 μm to 4 μm, fluorescence decay profiles of the donor follow the Förster resonance energy transfer (FRET) mechanism at high acceptor concentrations. Even though the decay rate of the pure donor remains unchanged, the efficiency of FRET is enhanced by a factor of two in smaller microcavities (diameter ∼4 μm) as compared to that of the bulk. The observed FRET rate is found to be 10 3 times larger than the radiative energy transfer rate for low Q-microcavities. Increase in the overlap integral due to whispering gallery modes (WGMs) of the microcavity accompanied by the decrease of inter-molecular distance gives rise to the observed enhancement. © 2011 Elsevier B.V. All rights reserved.