Experiments on single colloidal quantum dots (QDs) have
revealed
temporal fluctuations in the emission efficiency of the single-exciton
state. These fluctuations, often termed “blinking”,
are caused by opening/closing of charge-carrier traps and/or charging/discharging
of the QD. In the regime ofstrongoptical excitation,
multiexciton states are formed. The emission efficiencies of multiexcitons
are lower because of Auger processes, but a quantitative characterization
is challenging. Here, we quantify fluctuations of the biexciton efficiency
for single CdSe/CdS/ZnS core–shell QDs. We find that the biexciton
efficiency “blinks” significantly. The additional electron
due to charging of a QD accelerates Auger recombination by a factor
of 2 compared to the neutral biexciton, while opening/closing of a
charge-carrier trap leads to an increase of the nonradiative recombination
rate by a factor of 4. To understand the fast rate of trap-assisted
recombination, we propose a revised model for trap-assisted recombination
based on reversible trapping. Finally, we discuss the implications
of biexciton blinking for lasing applications.