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 year s ago, observations of blueshifted fluorescence have been widely used as a marker and measure of non-linear excitation, In doped crystals or in molecu lar multi-chromophore systems, where resonance energy transfer conveys exci tation from the sites of initial photoabsorption to others which yield the fluorescence, this process can play a possible intermediary role in the gen eration of two-photon fluorescence. Recent work has revealed other competin g mechanisms, involving energy transfer between three fluorophore sites, th at should be equally or more significant in strongly pumped systems dependi ng 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 o f the conditions under which it may be observed. Copyright (C) 2000 John Wi ley & Sons, Ltd.