Kinetics of radiationless energy transfer from upper excited states

A model of the kinetics of radiationless energy transfer from upper excited states is presented, where both the possibility of back energy transfer from the excited acceptor to a lower lying level of the donor and the possibility of energy migration over acceptors is considered. The model leads to a complex variation of the energy transfer quantum yield with the acceptor concentration. This dependence results from the interplay of direct energy transfer, back energy transfer and energy migration. Back energy transfer reduces the efficiency of donor-acceptor overall transfer efficiency. On the other hand, energy migration over the acceptors decreases the efficiency of back energy transfer and results in an increase in the energy transfer quantum yield. The known experimental results of energy transfer from upper excited states are in qualitative agreement with the present treatment.