Multicolor-Emissive Carbon Dots for White-Light-Emitting Diodes and Room-Temperature Phosphorescence

Multicolor tuning is one of the most remarkable features of carbon dots (CDs), used as a color convertor in making white-light-emitting diodes (WLEDs). Herein, a solvent-controlled method has been employed to prepare the multicolor-emissive CDs from 1,2,4-triaminobenzene and melamine, where the green-, orange-, and red-color-emissive carbon dots (G-, O-, and R-CDs) have been synthesized in acetone, water, and dimethylformamide (DMF), respectively. It has noted that the reaction solvent has impacted the growth of the particle size, elemental concentration, surface functionalization, and ultimately fluorescence emission. To avoid aggregation quenching emission (AQE), fluorescent polymeric films have been shaped by mixing poly(methyl methacrylate) (PMMA) with R- and G-CDs, while O-CDs was made with poly(vinyl alcohol) (PVA). Interestingly, PVA exhibited red-shifted emission of O-CDs from 585 to 597 nm in O-CDs/PVA, while PMMA accompanied a blue-shifting emission. The enriched nitrogen and oxygen elemental contents, especially the graphitic N of O-CDs/PVA, and hydrogen-bonding affinity of PVA cause the red-shifted emission of O-CDs/PVA. Fluorescent solid films have been used to develop monochromatic and white-color-emissive light-emitting diodes. Further, all of the synthesized CDs served as carbon precursors to develop room-temperature phosphorescence (RTP) by a molten salt method, where only R- and O-CDs achieved their RTP emissions with different intensities. The mechanism behind the RTP formation with particular CDs and their emission intensity dependency has been studied by the C═O moieties.