Exciton localization and migration in individual CdSe quantum wires at low temperatures

Low-temperature (< 40 K) photoluminescence (PL) spectra of individual CdSe nanocrystal quantum wires exhibit narrow (< 5 meV) isolated peaks spanning a range < 50 meV. We attribute these features to emission of excitons localized in shallow (a few meV deep) tight potential minima superimposed on longer-scale and larger-amplitude variations of the potential energy. Spectrally resolved PL dynamics reveal decreasing exciton-decay rates with decreasing emission energy. These observations are consistent with exciton relaxation within a manifold of localization sites characterized by an exponential density of states.