Auger Ionization and Tunneling Neutralization of Single CdSe/ZnS Nanocrystals Revealed by Excitation Intensity Variation

The dependence of the average times in on- and off-states of the fluorescence of a single semiconductor colloidal core/shell nanocrystal (so called quantum dot) on the intensity of the continuous laser excitation was studied. The mathematical expressions for the intensity dependence for on- and off-average times are obtained in the framework of a modified charging model, taking into account both the Auger ionization and tunnel neutralization mechanisms for transitions between neutral (on-state) and the ionized (off-state). The experiment with a single nanocrystal CdSe/ZnS shows that average on-time is proportional to 1/I 2, whereas the average off-time is nearly independent of the intensity, I. These results agree with processes of Auger ionization and tunneling neutralization of the core in core/shell nanocrystals.