Enhanced excitonic emission and visible luminescence of chemically synthesized ZnS:Co film phosphors

Abstract

Undoped and Cobalt doped ZnS thin films have been synthesised using chemical bath deposition technique. The X-ray diffraction pattern revealed a hexagonal structure for all the films. An increase in Co/Zn molar ratio resulted in a decrease in the intensity of diffraction peak corresponding to (100) plane and increase in crystallite size of the samples. The transmittance of the samples in the visible region was found to improve on doping. The optical band gap was found to vary from 3.46 to 3.66 eV with the incorporation of cobalt ions. The scanning electron microscope images of the samples exhibit a denser and more compact morphology for the doped films as compared to the undoped film. Photoluminescence studies reveal that all samples exhibit rare excitonic or near band-edge luminescence along with emissions in the visible region. The luminescence efficiency of ZnS film is appreciably enhanced with increase in concentration of the dopant.