Charge Carrier Localization Impact on the Spectral-Temporal Photoluminescence Separation in Type II CdTe/CdSe Nano-Heterostructures

Peculiarities of exciton dynamics in tetrapod-shapedCdTe/CdSenanocrystals (nanotetrapods) are revealed under various optical excitationconditions. The photoluminescence (PL) spectra exhibit a pair of wellresolved excitonic bands originating from CdTe and CdSe parts of thetetrapod arms as well as PL caused by the indirect transitions ofspatially separated charge carriers (CT band). We demonstrate thepump intensity dependent giant blue shift of the indirect transitionemission band caused by the exciton's space filling effectand the modification of energy level structure by the induced internalelectric field in both domains. The first-principles calculationsreveal that the ground states of both electrons and holes are localizedin the CdSe domain, but the charge carrier spatial separation is stillpresent, as holes are localized at the interface. This picture isproven by the time-resolved PL measurements from the sub-picosecondsto tens of nanoseconds range, which demonstrate the presence of apicosecond time scale corresponding to the indirect excitons beingmuch smaller than the previously observed value.

Automated summary

The peculiarities of exciton dynamics in tetrapod-shaped CdTe/CdSe nanocrystals are revealed under different optical excitation conditions. The photoluminescence spectra show well-resolved excitonic bands from CdTe and CdSe parts of the tetrapod arms, as well as PL caused by indirect transitions of spatially separated charge carriers. The giant blue shift of the indirect transition emission band, caused by the exciton's space filling effect and modification of the energy level structure by the induced internal electric field, is demonstrated.