A facile microwave-assisted synthesis of highly crystalline red carbon dots by adjusting the reaction solvent for white light-emitting diodes.

Microwave approach has been widely used for the synthesis of fluorescent carbon dots (CDs) due to its advantages of short reaction time and homogeneous heating. Currently, it is still difficult to synthesize red light-emitting CDs (R-CDs) via the microwave-assisted method at atmospheric pressure. Herein, we report a solvent-controlled synthesis of R-CDs using domestic microwave. As a result, for an ammonium citrate tribasic, formamide and glycerol blend reaction solvent, the R-CDs with emission peak of 622 nm were achieved and exhibited a photoluminescence (PL) quantum yield of 37.4% and excitation-independent PL emission spectrum. During the formation process of R-CDs, glycerol and formamide not only promote the carbonization of ammonium citrate tribasic, but can also enhance the crystalline nature of CDs. Finally, the warm white light-emitting diode (WLED) with a high colour rendering index (CRI) of 90.9 and Commission Internationale de L'Eclairage (CIE) coordinates of (0.344, 0.333) was realized by combining conventional yellow YAG:Ce phosphor and R-CDs/mesoporous silica (MPS) composites with a blue chip. This result demonstrates a low-cost R-CD synthetic method for potential substitution for red phosphor materials in solid-state lighting applications.