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Novel water-soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m-phenylenediamine as precursors were first synthesized using a onepot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu 3+ 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.

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As promising soft materials, various excellent properties of hydrogels have received widespread attention during recent years. Mechanical properties and self‐healing performance are required characteristics for hydrogels in practical applications. An important challenge is to develop hydrogels exhibiting mechanical performance and self‐recoverability through physical cross‐linking. In this work, the authors report a hydrogel consisting of a fully physically linked poly (vinyl alcohol)/agarose (PVA/AG) dual‐network, which is of high toughness and self‐healing properties. The synthesis process of the PVA/AG hydrogel is convenient, with AG as the first network, and hydrogen bonding and crystal‐associated PVA as the second network to form a dual physical crosslink. Due to this physical cross‐linking, the PVA/AG hydrogel has good mechanical properties (tensile strength of 6.5 MPa to 14.6 MPa, ductility of 168% to 214%). The highest compressive strength of hydrogel is up to 3.66 MPa, which is almost 8 times that of pure PVA hydrogel. In addition, it has excellent self‐healing properties without stimulation or healing agents. Compared to pure PVA hydrogel, PVA/AG hydrogels have higher thermal stability due to higher decomposition temperatures and lower degradation rates. In this study, the authors also initially explore the potential application of obtained hydrogel.

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