One-step synthesis of multicolor fluorescent carbon dots from neutral red for applications in LEDs and fingerprint detection

The development of simple and efficient synthesis strategies for multicolor fluorescent carbon dots (CDs) is crucial for advancing their applications in fields such as optoelectronic devices and fingerprint detection, and other fields. This study reports a “one-step synthesis combined with Thin Layer Chromatography (TLC) separation” strategy for the successful preparation of multicolor fluorescent CDs covering the entire visible spectrum (499-628 nm) under constant solvothermal conditions, using Neutral Red as the sole core precursor. The separated monochrome components—red (R-CDs), orange (O-CDs), yellow (Y-CDs), and green (G-CDs)—exhibit excellent optical properties, with R-CDs achieving a quantum yield (QY) as high as 20.3%. Systematic structural and spectral characterization reveals that the multicolor luminescence of these CDs does not originate from the conventional quantum confinement effect but is dominated by their surface states. The energy of these surface states is precisely tuned by the graphitization degree of the carbon core and the type of nitrogen-containing functional groups. Leveraging their superior optical properties and solid-state luminescence, the separated multicolor CDs were successfully applied in solid-state lighting to fabricate monochrome light-emitting diodes (LEDs) emitting bright orange, yellow, and green light, respectively. Furthermore, by compounding the highly luminescent R-CDs with starch, high-fidelity imaging of latent fingerprints (LFPs) was achieved, with second-level details being clearly visible. This research provides a new pathway for the low-cost production of multicolor fluorescent carbon dots, showcasing their broad application prospects in the field of advanced functional materials.