Green-Emissive Carbon Dots: Microwave Synthesis, Optical Properties, and Fluorescence Mechanism

Carbon dots (CDs) have attracted increasing attention due to their remarkable optical characteristics and broad application prospects. Here, we report an efficient and mild strategy for the rapid preparation of green-emissive CDs (G-CDs) via a microwave-assisted approach. The G-CDs were synthesized via microwave-assisted thermal treatment of m-phenylenediamine (m-PD) and phthalic acid in ethylene glycol for 10 min, followed by purification. The resultant G-CDs exhibit a bright green photoluminescence (PL) centered at 515 nm with an absolute quantum yield (QY) of 66.5%. Structural characterization revealed that the G-CDs possess a highly graphitized carbon core and are enriched with various surface functional groups. Mechanistic studies on fluorescence indicated that the green emission of G-CDs originates from the interaction between the surface-attached green fluorophore, phenazine-2,7-diamine (2,7-DAP), and the graphitized carbon core. In addition, the prepared G-CDs/polyvinylpyrrolidone (G-CDs/PVP) composite film exhibits excellent optical properties and was successfully applied in the fabrication of green light-emitting diodes (LEDs). This study might promote the understanding of the fluorescence mechanism and the development of preparation methods for high-performance G-CDs based on m-PD.