Public Research Seminar by Advanced Materials Thrust, Function Hub, HKUST(GZ) - Uncover a composite energy transfer mechanism in quantum dot superlattices by correlating exciton energy and diffusivity dynamics
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Quantum dot (QD) solids are promising optoelectronic materials; further advancing their function in devices is dependent on understanding their energy transport mechanisms. The commonly invoked near-field Förster resonance energy transfer (FRET) theory often underestimates the exciton hopping rate in QD solids, yet no consensus exists on the underlying cause. In response, we use time-resolved ultrafast stimulated emission depletion (TRUSTED) microscopy, an ultrafast transformation of STED microscopy to spatiotemporally resolve exciton diffusion in tellurium-doped CdSe-core/CdS-shell QD superlattices. We measure the concomitant time-resolved exciton energy decay due to excitons sampling a heterogeneous energetic landscape within the superlattice. The heterogeneity is quantified by single-particle emission spectroscopy. This powerful multimodal set of observables provides sufficient constraints on a kinetic Monte Carlo simulation of exciton transport to elucidate a composite transport mechanism that includes both near-field FRET and previously-neglected far-field emission/reabsorption contributions. Uncovering this mechanism offers a much-needed unified framework in which to characterize transport in QD solids and new principles for device design.
Rongfeng Yuan is a postdoctoral researcher in the group of Professor Naomi S. Ginsberg at UC Berkeley. Rongfeng’s research has focused on uncovering the electronic energy transport mechanisms in semiconducting materials by ultrafast optical microscopies. He received his Ph.D. in Chemistry from Stanford University, where he studied aqueous hydrogen bond network dynamics with ultrafast 2D infrared spectroscopy in Professor Michael D. Fayer’s group. He obtained the bachelor’s degree in chemistry from Peking University.