Tuning the Interfacial Stoichiometry of InP Core and InP/ZnSe Core/Shell Quantum Dots

We demonstrate fine-tuning of the atomic composition of InP/ZnSe QDs at the core/shell interface. Specifically, we control the stoichiometry of both anions (P, As, S, and Se) and cations (In, Zn) and correlate these changes with the resultant steady-state and time-resolved optical properties of the nanocrystals. Anion deposition on the InP QD surface results in a redshift in the absorption, quenching of the excitonic photoluminescence, and a relative increase in the intensity of the broad trap-based photoluminescence, consistent with delocalization of the exciton wavefunction and relaxation of exciton confinement. Time-resolved photoluminescence data show an overall small change in the decay dynamics on the ns timescale, suggesting the relatively low photoluminescence quantum yields may be attributed to the creation of new thermally activated charge trap states. Cluster-model density functional theory calculations show that the presence of core/shell interface anions give rise to electronic defects contributing to the redshift in the absorption.