EXCITON TRAPPING DYNAMICS AT VERY LOW-TEMPERATURES

We consider the decay of particles or excitations undergoing mechanical transport in a medium containing randomly-placed, irreversible trapping centers. We find, as observed earlier, that the trapping efficiency can be reduced for coherent excitations relative to the case where particle motion is diffusive. Indeed, our calculations show that in d-dimensions the untrapped fraction of coherent excitations should decay at very long times as a stretched exponential, P(t) ≈ exp[-Atd/(d+3)], which is asymptotically slower than that associated with diffusive transport. In strongly disordered media the decay can be substantially slower than this, exhibiting, e.g., a power law decay, with a power which depends upon the localization length of localized eigenstates near the band edge. © 1990.