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

• Published in: Chemphyschem Vol. 17; no. 5; pp. 731 - 740
• Main Authors: Bajwa, Pooja, Gao, Feng, Nguyen, Anh, Omogo, Benard, Heyes, Colin D.
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 03.03.2016; Wiley Subscription Services, Inc
• Subjects: Cadmium Compounds - chemistry; fluorescence; interfaces; lattice strain; Mathematical models; Microscopy, Electron, Transmission; Microscopy, Fluorescence; Oxides - chemistry; Quantum Dots; Selenium Compounds - chemistry; single-molecule studies; quantum dots; interfaces; fluorescence; lattice strain; single-molecule studies
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201500868

Choosing the composition of a shell for QDs is not trivial, as both the band‐edge energy offset and interfacial lattice mismatch influence the final optical properties. One way to balance these competing effects is by forming multishells and/or gradient‐alloy 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 the addition of inner shells of a single component versus gradient‐alloy shells of cadmium/zinc chalogenides onto CdSe cores, and then capping with a thin ZnS outer shell to form various core/multishell configurations. We show that architecture of the inner shell between the CdSe core and the outer ZnS shell significantly influences both the 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 multiexponential model. By binning the same data with 1 and 20 ms resolution, we show that the on times can be better described by the multiexponential model, whereas 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. What the Shell? We show that choosing the correct shell architecture is a complex problem, especially for multishell quantum dots. Different shell combinations, and whether they are alloyed or not, lead to different properties at the ensemble level (quantum yield) and the single‐particle level (blinking).