Improving the quantum yield of nitrogen-doped carbon dots by varying dopant ratios and pH

Herein, nitrogen-doped CDs (NCDs) were synthesized in a hydrothermal microwave-assisted pyrolysis using citric acid and urea. Differing carbon-to-urea molar ratios were used and the pH-dependent fluorescence and quantum yield (QY) at various pHs were measured. All NCDs demonstrated pH-dependent fluorescence with increased fluorescence from pH 1-13. Overall, the NCDs with a carbon-to-dopant molar ratio of 1:6 demonstrated the highest QY of 19% in pH 11. Additionally, high quantum yields were observed between pH 7-11. Therefore, NCDs, as prepared, may serve as cost-effective fluorescent pH sensors or in bioimaging applications.