Effect on photophysical properties of colloidal ZnS quantum dots by doping with cobalt, copper, and cobalt–copper mixtures

Colloidal ZnS quantum dots (QDs) are prepared by passing H2S gas through a solution of Zn(CH3COO)2 in acetonitrile. Photophysical properties are investigated using UV–Visible and photoluminescence (PL) spectroscopy. The spectrum shows an absorption shoulder at 271 nm representing a band gap of 4.6 eV. The doping of ZnS QDs with Co, Cu, and a mixture of Co and Cu not only increased the band gap to 0.2 eV but also turns these otherwise colorless QDs to blue in color due to cobalt, and green due to Cu. The observed emission in the visible region suggests that the dopants may have induced additional excited states to the ZnS QDs. This absorbance in the visible region can be utilized in the optoelectronic applications.