Impurity quenching of fluorescence in intense light. Violation of the Stern-Volmer law

The original integral encounter theory (IET) was used to describe the kinet ics and quantum yield of fluorescence in the presence of intense pumping li ght. We compare the energy quenching through an impurity induced interconve rsion, with energy quenching produced by bimolecular charge transfer from t he excited donor to the acceptor of the electron. In the former case, the c onvolution recipe which expresses the quantum yield via the system response to delta-pulse excitation is confirmed under special conditions, while in the latter case it was shown to not be applicable at all. By means of IET w e found the stationary concentrations of excitations and ions and demonstra ted the qualitative violation of the classical Stern-Volmer law at high int ensity of pumping light. The modified form of this law was proposed instead and the light dependence of its constant was determined in the contact app roximation. (C) 2000 American Institute of Physics. [S0021-9606(00)51624-9] .