Exciton trapping and recombination in type ii CdSe/CdTe nanorod heterostructures

Trap states are known to influence the excited-state dynamics in nanocrystalline semiconductors, but the nature and magnitude of the exciton - trap interaction is poorly understood owing to the relative optical inactivity of carrier traps and the heterogeneity of trap-state distributions. Nanocrystal time-resolved fluorescence measurements are typically complex traces that contain information about both radiative and nonradiative processes. The interpretation of these fluorescence transients is nontrivial, and typical multi- or stretched exponential analyses yield little specific photophysical information. Here, we develop a stochastic model of nanocrystal exciton and trap-state dynamics, which is used to describe coupled excitonic and charge-transfer photoluminescence from a series of CdSe/CdTe collinear quantum rod heterostructures. In this way we evaluate the photoexcitation dynamics of core nanocrystal states: the CdTe exciton and CdSe(e^-) -CdTe(h ⁺) charge-separated state and states associated with one or more trapped charge carriers. We describe the overwhelming influence of traps on the population dynamics and resolve population changes caused by the addition of a surface passivating ligand. Additionally, the long radiative lifetimes of the charge-separated state are reported.