Time-Resolved Förster Energy Transfer from Individual Semiconductor Nanoantennae to Single Dye Molecules

Abstract

Single semiconductor nanocrystals can be used as nanoscale optical antennae to photoexcite individual dye molecules in an ensemble via Förster energy transfer. Energy transfer on the microscopic level between a single donor and acceptor depends on the individual spectral overlap of absorption and emission of the single entities as well as on their spatial separation. We recently demonstrated how the spectral overlap between a single donor and a single acceptor can be tuned electrically using the Stark effect. Here, we investigate the effect of the average donor−acceptor spacing on the time-resolved fluorescence dynamics of single donor−acceptor pairs. The single nanocrystal donor luminescence is completely quenched for an average intermolecular separation of the dye of 9 nm. As the dye acceptor concentration decreases, both the number of donors observed and the average donor intensity increase due to an increase in nanocrystal fluorescence lifetime. At the same time, a temporal rise in the acceptor luminescence becomes discernible. The scatter in donor lifetimes observed increases with increasing acceptor concentration and is attributed to spatial disorder controlling the microscopic energy transfer rates.