Controllable Synthesis of Multicolor-Light-Emitting Carbon Dots via Gas–Liquid Repetitive Pulsed Discharges: The Role of Graphitic Nitrogen

In recent years, multicolor-emissive carbon dots (CDs) have garnered widespread attention owing to their versatile applications across diverse disciplines. Despite significant progress, developing efficient fabrication strategies and understanding fluorescence modulation mechanisms still pose considerable challenges. Herein, a fast and controllable method is reported to produce fluorescence-tunable CDs through gas–liquid discharge. Bright cyan, yellow, and red-emitting CDs are successfully prepared within 20 min via discharge treatment of m-phenylenediamine, o-phenylenediamine, and p-phenylenediamine aqueous solutions. These three types of CDs have similar average particle sizes of 4–6 nm, and their surfaces are functionalized with hydroxyl, carbonyl, amino N, and graphitic N. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses reveal that surface states primarily govern the fluorescence behavior of multicolor-emissive carbon dots. Quantitative analysis of N-induced surface states and DFT calculations demonstrate that the fluorescence-tunable mechanism is attributed to increased graphitic N content. Owing to their multicolor emissions, the synthesized fluorescence-tunable CDs excel in applications such as fluorescent films and LED devices. This work offers a pathway for fabricating diverse CDs by selecting various phenylenediamine isomers.