The photoluminescence (PL) kinetics of semiconductor nanocrystals (quantum dots, QDs) includes a surprisingly wide range of times. The presence of shallow metastable trap states leads to the appearance of a long tail on the PL decay curve, the so-called delayed PL, at times ranging from hundreds of nanoseconds to microseconds. Surprisingly, intensity and lifetime of the delayed PL from a single QD notably fluctuate in time. In this work, delayed PL of single colloidal core/shell CdSeS/ZnS QDs was in depth studied by time-gated PL traces analysis. Observed delayed PL blinking allowed us to study the shallow trap states. We show that single QD PL in active trap state is characterized by mono or bi-exponential decays with times altering from 60 ns to 600 ns, that is much exceed exciton lifetime in bright state ~30 ns. Simulation allowed us to conclude that the absence of an exciton component in the kinetics of delayed PL can be explained by the fast (~100 ps) charge carrier Auger trapping process on a shallow trap state. We associate this state with a localized defect at the inner core/shell QD interface. Also, we demonstrate that the variation in the lifetimes and delayed PL decay shapes can be described entirely by a change in the thermal de-trapping rate.
Kniazeva et al. (2026) studied this question.