The ability to generate and utilize multi-excited states in colloidal quantum dots (QDs) is key to a growing range of QD technologies. Studying multiexciton fluorescence dynamics in QDs is, however, often very difficult due to fast non-radiative Auger recombination. Recent work in our group has demonstrated that gold nanostructures, which are able to collect and focus light over very small length scales, can effectively switch on multiexciton emission when positioned in proximity to QDs. This effect has previously been observed for single excitations in QDs and molecules, but the ability to manipulate emission and absorption cross sections of multiply excited states using gold could have some important implications for a range of technologies and is leading to new insights about the dynamics of multi-excited states in QDs.
In this seminar I will discuss recent single particle fluorescence data that show dramatic enhancement of biexciton emission in the presence of nanostructured gold. Some of the factors that control the magnitude of this plasmonic coupling will be illustrated and the implications for optoelectronic devices will be discussed. Extending these measurements to ensemble samples has been made possible using a new multipulse fluorescence experiment that enables us to distinguish biexciton and trion emission from exciton emission. I will demonstrate this technique and illustrate its use to selectively probe multiexciton emission enhancement in a range of QD-gold structures. We will discuss the distance dependence of this interaction and present evidence that suggests the plasmonic coupling with multiexcitons is stronger than coupling with excitons.