Thermally stimulated luminescence of PbS quantum dots with various interface passivators

Abstract

The study aim is to establish the effect of various interface passivators (thiocarboxylic acids: thioglycolic acid (TGA), 2-mercaptopropionic acid (2-MPA), 3-mercaptopropionic acid (3- MPA); amorphous SiO2 shell) on the thermally stimulated luminescence of PbS quantum dots (QDs) with close value of the average nanocrystals size, which are equal to 3.0 ± 0.5 nm. All samples of PbS QDs, passivated with thiocarboxylic acids are characterized by exciton luminescence at 1120 nm and trap state luminescence in the region of 1200–1300 nm. The formation of PbS/SiO2 core/shell QDs leads to the trap state luminescence quenching in the region of 1200–1300 nm. Two types of shallow traps with a depth of 0.17 eV and 0.25 eV were found for PbS QDs, using the thermally stimulated luminescence technique in the temperature range from 80 K to 350 K. The formation of PbS/SiO2 core/shell QDs leads to a decrease in the concentration of traps with a depth of 0.25 eV, which indicates their interface nature. The obtained results indicate that the increase in the quantum yield of exciton luminescence at 1120 nm and of trap state luminescence quenching in the region of 1200–1300 nm during the formation of PbS/SiO2 core/shell QDs is the result of defects passivation with two types.