Mechanisms for charge trapping in single semiconductor nanocrystals probed by fluorescence blinking

Semiconductor nanocrystal optical and charge transport properties are largely influenced by the trapping of charge carriers on the nanocrystal surface. Charge trapping increases the non-radiative exciton decay pathways, thus decreasing the fluorescence quantum yield, and it also impedes efficient charge transfer at the nanocrystal interface. On a single nanocrystal basis, charge trapping causes interruptions in the otherwise continuous fluorescence known as fluorescence intermittency or blinking. In this tutorial review we examine the relationship between charge trapping and fluorescence blinking. The fluorescence microscopy techniques and statistical analysis methods used to measure single nanocrystal blinking are introduced. The development of numerous blinking mechanisms is reviewed, as is the physical nature of charge trapping sites. An overview of blinking experiments used to probe specific mechanisms for charge carrier trapping is presented. Finally, a summary and outlook are offered. Although the detailed mechanism is not fully understood, blinking experiments are found to provide direct evidence for several charge trapping mechanisms and report on changes to the nature and distribution of charge trapping sites.