Synthesis and Optoelectrochemical Properties of ZnS:Co Semiconductor Quantum Dots

Co2+ doped ZnS semiconductor quantum dots (QDs) were synthesized in an aqueous solution at 70 degrees C using citric acid (CA) or mercaptopropionic acid (MPA) as a stabilizer. The as-prepared undoped and the Co2+ doped ZnS quantum dots (QDs) were characterized by UV-Vis spectrum, photoluminescence (PL) spectrum, X-ray powder diffraction (XRD), cyclic voltammetry, and transmission electron microscopy (TEM). We studied the dependence of the doped ZnS quantum dots photoluminescence on the dopant and the dopant concentration. Results show that Co2+ ions are doped mainly on the ZnS nanocrystal's surface and as a result, the band-edge and surface defect emissions of the ZnS quantum dots are substituted by a Co2+-related PL emission. The best photoluminescence intensity was obtained for the 5% (molar fraction) cobalt doped ZnS quantum dots with MPA as the stabilizer. The cobalt doped ZnS quantum dots are 4 nm in diameter and are monodispersive.