Energy localization in substitutionally disordered solids. II. Studies by optical and optically detected magnetic resonance spectroscopy

In continuation of previous work, we present experimental measurements on the localization of triplet Frenkel excitons in isotopically doped phenazine and 1,4-dibromonaphthalene (2-D and 1-D effective excitation transfer topology, respectively). Dependence of steady state impurity aggregate (monomer, dimers, etc.) emission intensities on temperature, concentration of dopant, and the dimensionality is experimentally measured and theoretically modeled. Effects of phonons and excited state lifetimes are explicitly included in a numerical simulation of the data by average-lattice rate equations. The rate equations explain the major features of the experimental data quite well. For use in the rate equations, we have performed Monte Carlo experiments to determine cluster probabilities on 1-D and anisotropic 2-D lattices. Finally, the relevance of these findings to Anderson localization and percolation theory is discussed.