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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