Surface and interface effects on non-radiative exciton recombination and relaxation dynamics in CdSe/Cd,Zn,S nanocrystals

- We examine a CdSe/Cd,Zn,S core/shell system with a smoothed core/shell interface.
- We see homogeneity of emitters from single exponential lifetime.
- Biexciton recombination rate extended due to decrease in trap states at interface.
- Increased induction time for multiexciton recombination.
- Rate of electron cooling slowed due to increase in Auger relaxation rate.

Excitonic state-resolved pump/probe spectroscopy and time correlate single photon counting were used to study exciton dynamics from the femtosecond to nanosecond time scales in CdSe/Cd,Zn,S nanocrystals. These measurements reveal the role of the core/shell interface as well as surface on non-radiative excitonic processes over three time regimes. Time resolved photoluminescence reports on how the interface controls slow non-radiative processes that dictate emission at the single excitonic level. Heterogeneity in decay is minimized by interfacial structure. Pump/probe measurements explore the non-radiative multiexcitonic recombination processes on the picosecond timescale. These Auger based non-radiative processes dictate lifetimes of multiexcitonic states. Finally state-resolved pump/probe measurements on the femtosecond timescale reveal the influence of the interface on electron and hole relaxation dynamics. We find that the interface has a profound influence on all three types of non-radiative processes which ultimately control light emission from nanocrystals.

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