Theory of enhanced energy transfer between molecules embedded in spherical dielectric particles

The effects of morphological resonances on radiative emission rates and on dipole-dipole energy transfer rates between molecules embedded in aerosol droplets are studied by developing and applying a theory based on electromagnetic solutions for a dielectric sphere. Expressions for the Mie-resonance contributions to the transfer and emission rates are obtained in terms of the experimentally measurable spectral shape functions for the donor and acceptor molecules in the bulk host medium. Mie resonances in droplets of about 10 μm diameter are found to cause only minor changes in the integrated radiative rate, while strongly enhancing the rate and quantum efficiency of energy transfer. Estimates of the enhancement effect and calculations of its dependence on donor/acceptor location yield results consistent with experiment, supporting our interpretation that the observed energy-transfer enhancement occurs via Mie resonances of the nearly spherical droplets, and providing further insight into the Mie-enhanced energy-transfer mechanism.