An accretive mechanism for blue-shifted fluorescence in strongly pumped systems: resonance energy transfer with Raman emission

Since Kaiser and Garrett's pioneering work on two-photon absorption 40 years ago, observations of blue-shifted fluorescence have been widely used as a marker and measure of non-linear excitation. In doped crystals or in molecular multi-chromophore systems, where resonance energy transfer conveys excitation from the sites of initial photoabsorption to others which yield the fluorescence, this process can play a possible intermediary role in the generation of two-photon fluorescence. Recent work has revealed other competing mechanisms, involving energy transfer between three fluorophore sites, that should be equally or more significant in strongly pumped systems depending on the conditions. It is the purpose of this paper to identify fully the characteristics of one such process involving the coupling of fluorescence energy transfer with Raman emission, and to determine the precise nature of the conditions under which it may be observed.