Role of the Inner Shell Architecture on Quantum Yield and Blinking Dynamics in Core/Multi-Shell Quantum Dots

摘要

Choosing the composition of the shell for QDs is not trivial, since both the band-edge energy offset and interfacial lattice mismatch play roles in influencing the final optical properties. One way to balance these competing effects is by forming multi-shells and/or gradient-alloyed shells. However, this introduces multiple interfaces and their relative effects on quantum yield and blinking are not yet fully understood. Here we undertake a systematic, comparative study of adding inner shells of single composition vs gradient-alloyed shells of cadmium/zinc chalogenides onto CdSe cores, and then capping with a thin ZnS outer shell to form various core/multi-shell configurations. We show that the inner shell architecture between the CdSe core and the outer ZnS shell plays a significant role in both quantum yield and blinking dynamics but that these effects are not correlated – a high ensemble quantum yield doesn’t necessarily equate to reduced blinking. Two mathematical models have been proposed to describe the blinking dynamics – the more common power-law model and a more recent multi-exponential model. By binning the same data with 1 ms and 20 ms resolution, we show that the on-times can be better described by the multi-exponential model while the off-times can be better described by the power-law model. We discuss physical mechanisms that might explain this behavior and how it can be affected by the inner shell architecture.