Solvent-Engineered Strategy Synthesis of Multicolor Fluorescent Carbon Dots for Advanced Solid-State Lighting Applications

At present, achieving tunable fluorescent carbon dots (CDs) with narrow full width at half-maximum (FWHM) and high fluorescence quantum yields (QYs) remains a significant challenge. In our study, l-tryptophan and o-phenylenediamine were utilized as precursors, systematically controlling their band gaps and surface states by varying the solvent type. The blue (B-CDs), yellow-green (YG-CDs), and red (R-CDs) fluorescent CDs were successfully prepared, with optimal excitation wavelengths (λ_ex) of 444, 537, and 597 nm, respectively. Especially, these multicolor CDs (M-CDs) exhibited impressive QYs of 53.69, 54.88, and 58.79%, and narrow FWHM of 71, 64, and 34 nm, respectively. Their distinct optical properties were achieved by manipulating the carbonization and dehydration processes through a solvent selection. The variations in optical properties were primarily attributed to increased amino nitrogen content, quantum size, and coordinated effects of surface oxidation states. Furthermore, M-CDs were successfully incorporated into polyvinyl alcohol (PVA) to produce transparent and flexible fluorescent films, demonstrating their excellent and stable optical quality. Finally, the potential of M-CDs in optoelectronic applications was showcased by fabricating bright light-emitting diodes (LEDs).