Investigation from chemical structure to photoluminescent mechanism: a type of carbon dots from the pyrolysis of citric acid and an amine

Carbon dots (CDs) are one of the advancing fluorescent materials, which draw increasing attention in both theoretical research and practical applications. However, the clear chemical structure and photoluminescence (PL) mechanism of CDs is still an open debate, which limits the development of CDs. Because of the diversity of CDs, it is highly important to clarify this issue for specific CDs models. Herein, a type of CDs, made from citric acid with extremely high quantum yield, is investigated. Through the separation of the CDs, a type of bright blue fluorophore (IPCA) was discovered. IPCA and its derivatives were investigated and they were proven to contribute to the molecular state PL. Other components in the CDs were related to the carbon core state PL, which included polymer clusters and nanosized carbon cores. We conclude that this type of CDs contained complex components and multiple PL centers and that an independent fluorophore strongly affects the PL properties of the CDs. These two conclusions can potentially be true for similar CDs.