Synthesis and energy structure of optical transitions of the nitrogen and sulfur co-doped carbon dots

A green and efficient strategy was developed for one-step synthesis of sulfur and nitrogen co-doped carbon dots using urea, thiourea and thioacetamide as nitrogen and sulfur source and citric acid as carbon source. The influence of nitrogen and/or sulfur doping of the carbon dots on their optical transitions is investigated. The as synthesized carbon dots are demonstrated to possess redshifted photoluminescence with relatively high intensity. It is demonstrated that the presence of heteroatoms leads to the red shift of the photoluminescence band and increase of the crystalline phase inherent to amorphous carbon.