Impact of Precursors on Optical Properties of Fluorescence Carbon Dots

Size and surface state are most important factors affecting optical properties of Carbon Dots (CDs). In this work, citric acid as the primary precursor with two different types of secondary precursors (ammonium fluoride, thiourea) were employed for synthesizing CDs through one step and simple method in reflux condition. The property of the resulted materials was investigated on the base of optical absorption and emission. By results, maximum absorption edge was reached to 570 nm in high content of citric acid in presence of ammonium fluoride or thiourea. This indicates that absorption edge has been shifted to the higher wavelengths because of the nitrogen content in the resulted samples. No evidence of sulfur or fluoride atoms was observed in FTIR analysis however nitrogen doping was revealed by the formation of C=N bounds in the structure. Photoluminescence (PL) spectrums showed that surface recombination centers has been increased in presence of second precursor and non-uniformity of the structure was revealed in presence of ammonium fluoride. TEM image illustrated that the synthesized CDs were in the range of 20 to 50 nm.