Defocused wide field fluorescence imaging of single CdSe/ZnS quantum dots

Within this Letter, we demonstrate the application of defocused wide field fluorescence imaging to single CdSe/ZnS core shell quantum dots to obtain information on their orientation as well as on their transition moment. The emission intensity patterns obtained by the defocused imaging are compared to numerical calculations and reveal, that most of the quantum dots studied, possess an elliptical 2D transition moment, in contrast to the generally assumed circular 2D transition moment.