Charge and Surface Effects on Exciton and Hot Carrier Relaxation in Colloidal Quantum Dots

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Non-technical abstract:Over the last twenty years, semiconductor nanostructures have revolutionized optical technology with wide impact in communication and consumer electronics. Chemical synthesis of smaller, soluble, possibly better defined or more complex nanostructures promises to expand the impact to medical imaging, displays and solar energy. These Technologies are aggressively pursued by several venture firms. However, poor device efficiency and limited lifetimes may turn out to be show- stoppers. They are ultimately defined by the mechanisms of dissipation of the electronic energy in these tiny structures. In particular, it is becoming clear that the strong charge repulsion and the extreme surface proximity lead to very fast energy loss by yet unclear mechanisms. Understanding the generic mechanisms of the microscopic efficiency loss will be of broad importance in nanotechnology. This is the topic of this basic materials science project with physics and chemistry PhD students. The students will receive training in several research technique used in the study of these materials which will play important role in various products.Technical abstract:The project focuses on colloidal semiconductor quantum dots and how charge and surface affect their interband and intraband energy relaxation. The former is relevant to light-emitting diode or solar cell developments, while the latter may lead to infrared applications. The project quantifies how excess charge affects the stability, photo-excitation, fluorescence and relaxation. Experiments are performed on charged ensemble as well as single dots. Slow intraband relaxation would open new opportunities in engineering the nanostructure as well as in infrared applications and to date it appears to be strongly affected by the surface. The materials synthesis focuses on surface control and core/shells while the characterization involves time-resolved optical spectroscopy. The project supports the research of two PhD students at the interface of Chemistry and Physics. It also provides the scientific environment for one summer undergraduate, while the fluorescent materials are regularly used in classroom demonstration. Graduate students will receive training in broad spectrum of research technique used in the study of these materials which will play importnat role in various products.