Dispersive exciton transport in a hopping system with gaussian energy distribution

Employing the Monte Carlo simulation method, diffusion of excitons within a cubic lattice consisting of 29 x 29 x 29 sites with gaussian distribution of site energies (half width sigma) has been simulated. The computations yielded the probability distribution that a particle visits a certain number of new sites within a given time tau for a variety of sigma/kT values. The inherent exciton lifetime imposes an upper bound on tau. It has been shown that the exciton diffusion coefficient is time dependent, D(t) = D0(t/t0)sup(α)-1 + Dsub(infinite), where α is a measure for the degree of dispersion of the exciton motion. Transition from dispersive to gaussian transport, characterized by Dsub(infinite), occurs after a particle becomes thermalized within the distribution of energy sites. This requires that a particle visits about 300 new sites. The implication of the results on incoherent energy transport by singlet and triplet excitons as well as on exciton trapping is discussed. Agreement with literature data on singlet exciton motion in PVK is excellent. (orig.)