Influence of the energy transfer in a single donor–acceptor pair on the photon distribution functions in its fluorescence

Fluorescence of a single donor–acceptor pair is considered. A donor molecule is described by a three-level energy scheme. It has a ‘dark’ state, which makes donor fluorescence blinking. An acceptor molecule is described by two-level scheme. Its fluorescence is of continuous type. Strong dependence of the distributions w N D ( T ) and w N A ( T ) for photons emitted by the donor and the acceptor on the electronic excitation energy transfer rate F between the two molecules is demonstrated. For instance, at F ≅ 1 / T D , where 1 / T D is the donor fluorescence rate, the fluorescence of the two-level acceptor starts blinking. The photon number distributions at F ≪ 1 / T D u F ≫ 1 / T D are considered as well.