This paper investigates the direct, incoherent energy transfer due to exchange from an excited donor to randomly distributed acceptors. Making use of a general, exact formula for the time and concentration dependent ensemble averaged decay lsqb;Blumen and Manz, J. Chem. Phys. 71,4694(1979) rsqb; simple approximate expressions for the limiting cases, of low and high concentrations and of short and long times, also under the inclusion of the backhyphen;transfer in the pair approximation, are derived; for low acceptor concentrations and long times the results of Inokuti and Hirayama lsqb;J. Chem. Phys. 43, 1978 (1965)rsqb; generalized to arbitrary dimensions, are retrieved. The limits of validity of the different approximations are determined by a numerical evaluation of the exact formula for particular lattices of interest.
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