Shedding light on multicarrier properties in semiconductor nanocrystal
Over the last three decades semiconductor nanocrystals have proven to have a wide range of applications in both emissive and absorptive technologies. Due to high emission quantum efficiencies, facile tunability of the emission wavelength, high molar absorptivities, and relatively long excited state lifetimes, a wide range of nanocrystal applications have been realized such as high color range displays and energy harvesting in photovoltaic and photocatalytic systems. A further advantage of nanocrystal systems is they can sustain multiple simultaneous excitations in the form of multiexcitons, or even simply excess carriers, without significantly altering the energy of the state. In particular, multicarrier states have been used to generate nanocrystal lasers where the lasing state is the biexciton (two excitons) and for energy transfer applications. Thus, the energy and lifetime of these highly excited states are of significant importance to successfully harnessing multicarrier states for targeted applications. In this talk I will present results from my graduate and postdoctoral work on both Cd-chalcogenide and cesium lead halide perovskite nanocrystals characterizing a variety of multicarrier states. First, I present a mechanism for generating an excess charge in photocatalytically relevant CdS nanocrystals which persists for minutes to hours in solution. Next, I turn to CdSe nanocrystals and illustrate the power of combining absorptive and emissive methods to fully understand the energy, lifetime, and recombination pathway of both the biexciton (two electron-hole pairs) and triexciton (three electron-hole pairs). Finally, I compare these results to cesium lead halide perovskite nanocrystals and discuss the effects of quantum confinement and lattice mobility on multicarrier states.
Hosted by Professor Wilma Olson
~Coffee/tea will be served prior to the lecture~