Ultrafast photoinduced charge dynamics in colloidal CdSe/CdS quantum dots in toluene

Abstract

We studied the dynamics of photoinduced charge carriers in core/shell CdSe/CdS quantum dots (QDs) of two sizes, 2.0 and 2.9 nm, in a toluene colloid by femtosecond up-conversion spectroscopy. We observed the luminescence kinetics of QDs excited by 50 fs laser pulses at a wavelength of 385 nm. The modeling of experimental data showed that a 0.5 ps rise of the luminescence intensity corresponds to the process of electron thermalization. The two-exponential luminescence decay with characteristic times in the picosecond range corresponds to populating of two types of traps, which we associate with core and shell defects. Electron–hole recombination process does not affect the shape of the luminescence kinetics in the picosecond range. A comparative analysis indicates that the concentration of defects in 2.0 nm QDs is greater than that in 2.9 nm QDs, while potential wells, which charge carriers eventually escape due to thermal activation, are deeper for 2.9 nm QDs.