While many applications of nanocrystalline semiconductor quantum dots (QDs) involve large numbers of particles packed into small volumes—such as films for photovoltaic devices—to ensure effective coupling of energy into or out of the system, the true coupling efficiency involves inter-particle interactions at the single-particle scale. Absorption and emission spectral properties, geometry and distance of neighboring particles, and the relative orientation of the QDs strongly influence the coupling efficiency among the particles. In particular, the orientation of the transition dipole moments of a donor-acceptor pair can change the coupling efficiency by an order of magnitude and is difficult to measure. Here, we present a new imaging method that measures the orientation of the donors and acceptors of QD pairs and resolves the emission from the emitters with 5 nm resolution. Knowledge of the location and orientation of each emitter is then measured against the expected energy transfer rate equation for Förster Resonance Energy Transfer (FRET) theory. Because this is a single-particle approach, the variety of possible coupling configurations (orientation, spectral overlap, and separation) can be sorted into the specific mechanisms that are responsible, in contrast to ensemble-level measurements, and more narrowly direct the engineering of films for improved efficiency.

Dual-color and polarization super-resolution imaging: Investigation into energy transfer efficiency among donor-acceptor groups of quantum dots

2019 Spring National Meeting

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