CONCENTRATION-DEPENDENCE OF LUMINESCENCE DECAY TIME OF MOLECULES IN ISOTROPIC MEDIA

Assuming that only monomers and non-luminescent dimers appear in the solution and non-radiative electronic energy transfer results from a dipole-dipole interaction we have obtained an expression for the dependence of luminescence decay time on the reduced concentration γ of the dye molecules in the solution. In order to compare the obtained theoretical results with the experiments, measurements have been carried out on the concentration changes of luminescence decay time of Na-fluorescein in glycerol-alcohol solutions. After corrections for reabsorption and influence of the secondary fluorescence, the obtained experimental results show a satisfactory agreement with the theoretical prediction. The subsequent slight increase and decrease of τ found at the increasing concentration can be attributed to the competition between the electronic excitation energy diffusion process among the monomers and the process of photoluminescence concentration quenching by dimers, as well as by monomers. © 1979 with the authors.