Luminescence of colloidal Ag2S/ZnS core/shell quantum dots capped with thioglycolic acid

The features of IR luminescence of colloidal Ag2S QDs passivated with thioglycolic acid (Ag2S/TGA) under the formation of Ag2S/ZnS/TGA core/shell QDs are considered. A 4.5-fold increase in the quantum yield of recombination IR luminescence within the band with a peak at 960 nm (1.29 eV), full width at half maximum of 250 nm (0.34 eV), and the Stokes shift with respect to the exciton absorption of 0.6 eV was found. The increase in the IR luminescence intensity of Ag2S/ZnS/TGA QDs is accompanied by an increase in the average luminescence lifetime from 2.9 ns to 14.3 ns, which is explained as healing of surface trap states during the formation of the ZnS shell. For the first time, the enhancement of the luminescence intensity photodegradation (hereinafter referred to as fatigue) was found during the formation of the Ag2S/ZnS/TGA core/shell QDs. The luminescence fatigue is irreversible. We conclude that the initial stage of photolysis of the Ag2S core QDs under laser irradiation plays a key role. Low-atomic photolytic clusters of silver formed on the Ag2S core QDs act as luminescence quenching centers and do not reveal structural transformations into Ag2S, provided that the clusters are not in contact with TGA.