OPTICAL PROPERTIES OF CdS–Ag2S QUANTUM DOT SYSTEM

Abstract

The paper presents the results of a study of systems with quantum dots of two types: CdS and Ag₂S, which have different types of crystal lattices. CdS quantum dots were synthesized in the gelatin matrix by means of the sol-gel method. The average size of CdS quantum dots with a cubic crystal lattice was 2-4 nm. During the synthesis of CdS quantum dots, silver ions were added into the reactor. The concentrations of their mole fractions per cadmium ions were as follows: С_Ag = 10^-2, 2.2 ∙ 10^-2, 4.6 ∙ 10^-2, 10^-1, 2.2 ∙ 10^-1, 4.6 ∙ 10^-1, 1 : 1. Starting with a concentration of С_Ag = 10^-2 and increasing it leads to the formation of Ag₂S quantum dots with a monoclinic crystal lattice and luminescence in the 1100-1300 nm spectral range. The intensity of this spectra increases with the increase in С_Ag. Within the range of С_Ag = 10^-2 - 2.2 ∙ 10^-1, a number of silver ions enter the CdS quantum dots in the form of a doping additive and create luminescence centres. This results in an increase in the intensity of the total luminescence band in the spectral region of 550–650 nm. A conclusion has been drawn that presence of sulphur, cadmium, and silver ions in the reactor during the synthesis leads to the formation of quantum dots of two types: CdS and Ag₂S. This system has two luminescence bands in visible and in near-infrared regions of the spectrum. Such materials can be used as emitting devices with luminescence bands in two different spectral regions.

ACKNOWLEDGMENTS

Quantum dots absorption spectra and images were obtained by means of TEM and X-ray diffraction patterns and were measured using the equipment of the Centre for Collective Use of Scientific Equipment of Voronezh State University.