pH-modulated synthesis of multicolor carbon dots from Perilla leaves for dual-mode room-temperature fluorescence and phosphorescence applications.

Biomass materials represent an ideal carbon source for synthesizing carbon dots (CDs) due to their abundance, elemental diversity, renewability, and low cost. This study presents a straightforward solvothermal method for synthesizing polychromatic carbon dots (MCDs) by systematically adjusting the reaction parameters using biomass-derived precursors (Perilla fruits leaves and tea polyphenols) under pH-modulated conditions (pH 2-13). The MCDs show tunable emission (395-646 nm), overcoming the traditional blue/green limitation of biomass-derived CDs. Mechanistic studies reveal that this spectral tuning arises from the synergistic control of particle size (1-5 nm) and the extent of C = C conjugated domain, facilitating long-wavelength emission. The optimized MCDs exhibit unique room-temperature dual-mode luminescence, including full-color fluorescence and long-life phosphorescence (lifetime ≈ 0.46 s), attributed to a covalent and hydrogen bond network that promotes efficient intersystem crossing. These MCDs exhibit multi-functional applications: (1) as an environmentally friendly means for white light-emitting diodes (WLED) with CIE coordinates of (0.30, 0.34), (2) for high-contrast latent fingerprint visualization, and (3) as advanced anti-counterfeiting ink with time-resolved encryption capability. This work not only establishes a green strategy for multicolor CDs derived from biomass, but also expands their potential in optical security and forensic science.