Critical concentration for electronic energy transfer in mixed organic solids

Abstract

We propose that inhomogeneous broadening of the diagonal site-excitation energies of impurity molecules in isotopically mixed organic crystals results in an Anderson transition from extended to localized electronically excited states. The critical impurity concentration estimated for the localization of all triplet states within the impurity band in isotopic mixtures of naphthalene was found to be compatible with the available experimental data. The concept of the minimum diffusion coefficient for electronic energy transfer in extended states just above the Anderson transition was introduced and estimated by the application of the random phase model.