Structural and optical properties of Ag2S/SiO2 core/shell quantum dots

Abstract

This paper presents an original two-step technology for water synthesis of Ag2S/SiO2 core/shell quantum dots (QDs) based on Ag2S QDs, passivated with thioglycolic acid with luminescence in the near IR region (800–1400 nm). The formation of Ag2S QDs with an average size of 2.5 nm, SiO2 coated with thickness of 1.3–4 nm has been established using transmission electron microscopy and energy dispersive X-ray analysis. The possibility to control the formation of Ag2S/SiO2 core/shell QDs using FTIR spectroscopy data is shown. The results show a change in the luminescence properties of Ag2S QDs with an increase in the thickness of SiO2 shell. They are i) an increase in the intensity and quantum yield of QD luminescence by 7 times during ligand exchange and up to 35 times as a result of a further increase in the thickness of SiO2 shell; ii) an increase in the average luminescence lifetime from 3.5 ns to 17.7 ns during the formation of SiO2 shell. These studies demonstrate a way to control the quantum yield of NIR recombination luminescence of colloidal Ag2S QDs and expand the ways of their application.