Enhanced Red Light Emission in Chemically Synthesized Cobalt Substituted ZnS Nanoparticles

The luminescent properties of II-VI semiconductors have attracted the attention of researchers due to their amazing optical and electrical properties and hence possible applications in the fields ranging from optoelectronics to imaging in biomedical. In the current study, the improved red emission observed in cobalt substituted polyvinylpyrrolidone capped zinc sulfide nanoparticles synthesised by chemical method is investigated. The cobalt doped zinc sulphide nanoparticles capped with polyvinylpyrrolidone were synthesized by a simple, single-step, chemical co-precipitation of precursors in ambient condition for various concentrations (1%, 2%, 5% and 10%) of the cobalt impurity. The absorption spectrum has an absorption edge at 324 nm for pure zinc sulphide with a shift to 321 nm with substitution of the dopant but does not changes significantly with the doping concentration. The x-ray powder diffractometry along with energy dispersive spectroscopy were utilised to affirmation of the formation of zinc sulphide nanoparticles and addition of cobalt ions in the crystal matrix of zinc sulphide. The crystallite size and morphology were determined with electron microscopy, x-ray powder diffractometry and UV-visible spectrograph (absorption edge & Tauc plot). Synthesized nanoparticles were of size about 2.6 nm having spherical shape and good in particle size distribution. A single, strong and sharp peak at 782 nm corresponding to red colour was observed in the photoluminescence spectra whose intensity varied with the amount of doping without any noticeable change of emission wavelength. The emission intensity increased with the impurity level, giving a maximum intensity for 1% impurity level and quenching thereafter.