Anomalous Exciton-Quenching Kinetics in Doped Polyacenes

The time-dependent rate of energy transfer, $k\left(t\right)\mathrm{}$, found by observation of sensitized fluorescence from certain organic mixed crystals, is analyzed in terms of results for the exciton master equation. A variety of possible explanations of the anomalous time dependence of $k\left(t\right)\mathrm{}$ are shown to be inconsistent with these results. A model that includes host traps which can slowly transfer energy back to the host is shown to give a good quantitative fit to the experimental $k\left(t\right)\mathrm{}$.