FRET-Mediated Collective Blinking of Self-Assembled Stacks of CdSe Semiconducting Nanoplatelets

Förster resonant energy transfer (FRET) can be
an efficient
energy transfer mechanism between densely packed fluorescent emitters.
It plays a key role in photosynthesis but may also be detrimental.
In optoelectronic devices for instance, FRET funnels energy to quenching
sites and favors losses. Here, we image individual self-assembled
chains of stacked CdSe nanoplatelets and demonstrate fluorescence
intermittency (blinking) of chain portions corresponding to a few
tens of platelets. This collective blinking is attributed to the fluctuations
of a quencher site, to which excitons are transferred by FRET migration
from the surrounding platelets. We develop an analytical random walk
model of the chain and show that an ensemble of platelets can be quenched
collectively by a single site provided that its quenching (nonradiative
recombination) rate is faster than the geometric mean of the radiative
recombination rate and the transfer rate, which for self-assembled
platelets would be of the order of (100 ps)−1.