Direct Visualization of Exciton Transport in Semiconductor Quantum Dot Nanostructures Using Time-Resolved Superresolution Microscopy*

A time-resolved superresolution microscope to localize single emitters with nanometer precision and image their lifetimes with sub-nanosecond time resolution is described. This technique has been used to image semiconductor quantum dot (QD) nanostructures composed of single QD emitters that interact via resonance energy transfer. Photoemission from the nanostructures is imaged onto a 2x2 optical fiber array, and the fiber outputs are monitored using time-correlated single photon counting. The relative intensities reveal changes in the emission center as the QDs blink on and off. Emission centers separated by 10-nm or less can be distinguished based on changes in intensity and lifetime that occur when energy is transferred from donor to acceptor QDs. The distribution of centroid positions provide a direct visualization of the energy transport pathway through the nanostrucure.