UV light‐tunable fluorescent inks and polymer hydrogel films based on carbon nanodots and lanthanide for enhancing anti‐counterfeiting

: Novel water-soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m-phenylenediamine as precursors were first synthesized using a one-pot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu3+ and pyridine-2,6-dicarboxylic acid. The optical properties of CNs were characterized using ultraviolet visible (UV) spectra and fluorescence spectra, microscopic morphology was characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the elemental composition was characterized using Fourier transform-infrared spectroscopy (FT-IR) and X-ray photoelectron spectra (XPS). The fluorescence spectra of the lanthanide complexes were also measured. A simple strategy was developed to prepare UV light-tunable fluorescent inks and polymer hydrogels films based on CNs and lanthanide complexes. The fluorescent inks and polymer hydrogels films could be repeatedly switched between green and red fluorescence. The change of color depended on luminescence of the CNs and the lanthanide complexes under 254 and 365 nm UV light, respectively. The UV light-tunable fluorescent inks and polymer hydrogels films could enhance its anti-counterfeiting function for data and information.