EFFECTS OF EXCITATION MIGRATION AND TRANSLATIONAL DIFFUSION IN THE LUMINESCENCE QUENCHING DYNAMICS

Luminescence decay in the presence of quencher is considered theoretically. Combined effects of molecular diffusion and excitation migration among energy-donors are treated within a unified framework. A set of general kinetic equations for describing the luminescence quenching dynamics is derived from a hierarchical system of many-body Smoluchowski equations for the reactant molecule distribution functions. Numerical and approximate analytic solutions to these equations for a simple model system show that the effective diffusion coefficient of donors upon a quencher can be considerably larger than the simple sum of translational diffusion coefficient and excitation-migration diffusion coefficient estimated for a system of fixed donor molecules. This finding is in accordance with a recent experimental result of Pandey et al. Another important finding is that the excitation migration diffusion coefficient should be proportional to the donor concentration CD0 in the large CD0 limit when the donor molecules are extremely mobile, while it varies with (CD0)4/3 for a system of immobile donors as is known. It is also shown that some well-known previous theories are incorrect at least in the fast excitation migration limit. © 1995 American Institute of Physics.