Study of higher-energy core states in CdSe/CdS octapod nanocrystals by ultrafast spectroscopy

We present a study of the intermediate energy transitions in octapod CdSe/CdS nanocrystals accomplished by ultrafast pump probe spectroscopy (150 fs resolution) combined with effective mass calculations. The bleaching features revealed in the differential transmission spectrum indicate that intermediate transitions occur from higher-energy hole states confined in the core, to the few electron states mildly localized in the core by the weak geometrical confinement. The detection of bleaching features of the intermediate states at long time implies that electron-hole recombination is inhibited in these structures, meanwhile electrons are available for further transport along the nanostructures. This information indicates that such nanostructures could be promising for photovoltaic applications.