Insight into the hybrid luminescence showed by carbon dots and molecular fluorophores in solution

Carbon dots have attracted great attention from the research community given their very attractive luminescent properties. However, the recent discovery that some of these properties may result from fluorescent impurities originating from the synthesis process, and not from the carbon dots themselves, constitute a significant setback to our knowledge of these materials. Herein, we proceeded to the study of carbon dots generated from citric acid and urea via a microwave-assisted synthesis, focusing on their analysis by AFM, HR-TEM, XPS, FT-IR, ESI-MS, UV-Vis and fluorescence spectroscopy. We have found that this synthesis process does generate molecular fluorophores that can mask the luminescence of the carbon dots. More importantly, our data demonstrates that when present in the same solution, the carbon dots and these fluorophores do not behave as separated species with individual emission. Instead, they interact to produce a hybrid luminescence, which excited state properties and reactivity are different from the properties of the individual species. These results indicate the possibility for the development of hybrid materials composed by carbon dots and related molecular fluorophores with new and improved properties.