Trap States in Semiconductor Quantum Dots: Friends or Foes

Photophysical attributes of semiconductor quantum dots (QDs) are influenced by the presence of undercoordinated ions on their surface, which generate new bands called trap states. These bands are located within the bandgap in II-VI and III-V systems; hence, their photoluminescence and electron transfer properties are also guided by the trap depth and density. Our efforts to understand these aspects are summarized here by taking CdSe and InP QDs as examples. The increase in photoluminescence efficiency in CdSe QDs with an increase in core size is attributed to the decrease in electron trap depth, allowing efficient detrapping of electrons. Stacking faults, another type of defect, is responsible for the enhanced photoluminescence blinking during the asymmetric shell growth of CdS on CdSe QDs. Investigation of photoinduced electron transfer dynamics further establishes deep trap states in InP QDs, compared to shallow trap states in CdSe QDs, and effective charge stabilization in the former.