Energy Transfer and Fluorescence Quenching of Eu³⁺ in Polyacrylamide-Konjac Mannan Composite Hydrogel

Fluorescent hydrogels have attracted much attention due to their excellent and unique photoluminescent properties, which makes it very necessary to explore their luminescent properties. In this study, a three-dimensional hydrogel system of polyacrylamide-konjac mannan - 2,6-pyridine dicarboxylic acid (PAM-KG-Ln) was constructed using the rare earth element Eu as the luminescence unit, and a series of PKL: xEu³⁺ fluorescent hydrogels were prepared by in-situ polymerization. The prepared hydrogels had excellent luminescence properties and a color purity of 99.4%. It was found that the strongest emission peaks of PKL: xEu³⁺ fluorescent hydrogels were located at 700 nm under excitation at 295 and 398 nm., which were derived from the ⁵D₀→⁷F₄ transition. In addition, it was found that the fluorescence quenching phenomenon occurred under the ultraviolet lamp with the increase of Eu³⁺ doping concentration, and then the spectral analysis combined with Van Uitert modeling revealed that the ⁵D₀ energy level quenching mechanism of Eu³⁺ was dominated by electric dipole-electric dipole interaction (Q ≈ 6), which provides a new paradigm for the design of dynamic fluorescent hydrogels, and is expected to promote the development of applications such as high-resolution biological probes and stimuli-responsive soft drives.