Ultrafast electron-hole dynamics in core/shell CdSe/CdS dot/rod nanocrystals

Colloidal semiconductor nanocrystals are nanoscale materials whose optical, electronic and transport properties, due to their strong dependence on size and shape, can be finely tuned by advanced chemical synthesis approaches. Among various types of semiconductor nanocrystals, core-shell nanostructures comprised of a semiconductor core that is covered by a thin shell of another type of semiconductor material have been extensively investigated. This paper investigates ultrafast carrier dynamics of core/shell CdSe/CdS dot/rod heterostructures by using femtosecond pump-probe transient spectroscopy in the visible spectral range to analyze. Upon tuning the pump photon energy and intensity, the core or the shell is selectively excited: the electronic structure and the wavefunction distribution at the rod/dot interface and the electron-hole dynamics within the nanostructure have been investigated. Results show that after charge carrier relaxation into the lower energy levels associated to the CdSe dot, the electron wave function extends into the rod: upon exciting the CdSe core an intense bleaching signal in the CdS spectral region is found which is due to the delocalization of the electronic wavefunction on the basis of envelop-function theoretical calculations.