Quenching of fluorescence by irreversible energy transfer at arbitrary strong pumping light

The irreversible inter-molecular energy transfer in solutions, acting as a mechanism of fluorescence quenching, is studied at an arbitrary strength of the pumping light. Using powerful methods of an original Integral Encounte r Theory, we prove that the fluorescent quantum yield obeys the generalized Stern-Volmer law, linear in concentration of the unexcited energy accepter s. In contact approximation we specify how this fraction depends on the tot al concentration of accepters at different lifetimes of excitations and an arbitrary excitation rate. The Stern-Volmer constant which is a function of the same parameters, either increases or decreases with light intensity de pending on how fast is the decay of excited acceptor. These non-linear effe cts provide additional information about the energy exchange mechanism and its parameters. (C) 2001 Elsevier Science B.V. All rights reserved.