DIFFUSION-LIMITED EXCITON FUSION REACTION IN ONE-DIMENSIONAL TETRAMETHYLAMMONIUM MANGANESE TRICHLORIDE (TMMC)

We present results of an experimental study on the reaction kinetics of a one-dimensional diffusion-reaction system, on a picosecond to millisecond time scale. Tetramethylammonium manganese trichloride (TMMC) is a perfect model system to study this problem. Time-resolved luminescence of TMMC has been measured over nine decades in time. The nonexponential shape of the luminescence decay curves depends strongly on exciting laser power. This is shown to result from a fusion reaction (A + A --> A) between photogenerated excitons, which is very well described by the diffusion-limited single-species fusion model for initial exciton densities < 2 x 10(-3) (fraction of the number of sites). At higher initial exciton densities the diffusion process, and thus the reaction rate, is significantly influenced by the heat produced in the fusion reaction. This is supported by Monte Carlo simulations.