Solvent-free microwave-assisted synthesis of solid-state yellow carbon dots with visible-light excitation for dual applications in fingerprint visualization and white LEDs.

A simple, scalable, and solvent-free route for producing solid-state emissive carbon dots (CDs) with visible-light excitation remains challenging, particularly for dual applications in latent fingerprint (LFP) detection and white light emitting diodes (LEDs). Herein, we report a microwave-assisted, solvent-free synthesis of yellow-emitting carbon dots (Y-CDs) using phloroglucinol and boric acid as precursors. The obtained Y-CDs exhibit uniform morphology (2.63 nm), strong solid-state yellow fluorescence with optimal excitation at 520 nm, and an absolute photoluminescence quantum yield of 22.5%. The material demonstrates excellent photostability, thermal degradation, and long-term storage stability. Owing to these properties, the Y-CDs enable high-contrast latent fingerprint visualization with clear Level III ridge features across multiple substrates with negligible background interference. Moreover, the Y-CDs were successfully integrated in white and monochromatic LED fabrication. A WLED was achieved by integrating Y-CDs with a 456 nm blue chip, yielding Commission Internationale de l'Éclairage (CIE) coordinates (0.329, 0.321) close to the ideal white point.