Synthesis of multicolor carbon dots at room temperature and in atmosphere toward energy-efficient preparation and LEDs application

In the reaction conditions of room temperature and atmosphere, the synthesis of carbon dots (CDs), especially those with multicolor, is of great potential since it allows for large-scale production. Herein, the multicolor CDs (MCDs) with blue, green, yellow and red colors were synthesized in one step at room temperature and in atmosphere without any external energy. Using o-phenylenediamine (o-PDA) as a precursor, N, N-Dimethylformamid (DMF) as solvent, the addition of different oxidants (HNO3, H2O2) and various polyol or polybasic acids makes the MCDs emitting diverse fluorescence colors. Based on structural characterization, the formation mechanism of MCDs can be explained that the energy released from oxidation, Schiff base and amindation reactions promotes dehydration, self-polymerization and carbonation, leading to MCDs successfully synthesized. The optical mechanism derived from both experimental and theoretical analyses demonstrates that particle size, graphitization and conjugated systems influence the emission wavelength of MCDs. Finally, the MCDs were successfully applied in down-converting LEDs with satisfied properties. This study provides an effective strategy to prepare MCDs with the concept of "energy-efficient chemistry" and potentially realizes industrial production.