A Novel Green Synthesis Method for the Preparation of Highly Fluorescent Carbon Dots for Security Ink Applications.

Environmentally benign biosynthesized carbon dots with diverse chemical and physical properties play an important role in today's scientific research. In the present study, a new approach utilizing dye extraction from betel leaf, followed by a rapid, additive-free dye-derived-hydrothermal process, to synthesize carbon dots with a high quantum yield. The synthesized carbon dots were characterized using UV-visible, Photoluminescence (PL), Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy. The UV-visible spectrum of the carbon dot exhibited two major peaks at 233 nm and 294 nm and a tail continuing into the value 342 nm corresponding to π→π* and n→π* transitions. The PL spectra for different excitation wavelengths exhibit a broad peak at 465 nm, attributed to the carbon dot's surface defect state. FTIR spectra confirmed the presence of various functional groups present in the sample. The formation of carbon dots with an average diameter of 3.4 nm was confirmed by transmission electron microscopy (TEM) images. Energy-dispersive X-ray (EDAX) analysis showed the presence of elements C and O in the prepared sample. The synthesized carbon dots with low toxicity, strong fluorescence, and excellent photostability demonstrate immense potential as biocompatible fluorescent ink in future security applications.