Abstract:
Semiconductor nanocrystals (also known as quantum dots, QDs) are solution processable, offering good photostability, high quantum yield, tunable and broad absorption, and narrow and tunable emission spectra. These properties make them promising materials for energy efficient lighting, low-cost photovoltaics, and biological sensing and imaging devices. Key elements that determine the optical and electrical properties of QDs are the properties of excitons (bound electron-hole pairs) in the QDs. We use confocal fluorescence spectroscopy and time correlated single photon counting method to study exciton and multiexctions in single QDs. More specifically, we investigate (1) photoluminescence behavior of excitons and triexcitons. (2) the photoluminescence quantum yield of biexctions. (3) the relationship between exciton photoluminescence behavior and biexciton quantum yield. The results contradict a widely accepted charging and Auger recombination model of non-radiative recombination in single QDs. We propose a model that involves both Auger and trap-assisted recombination that explains our results.