Rare‐Earth Coordination Hydrogels Enabling Self‐Powered and Self‐Luminous Closed‐Loop Systems

Rare-earth (RE) fluorescent hydrogels have emerged as promising candidates for sensing, encryption, and flexible display technologies. However, their reliance on external ultraviolet (UV) excitation severely hampers portability and integration into self-sustained electronic systems. Herein, we report a multifunctional Eu/Tb-doped hydrogel that uniquely combines stretchability, ionic conductivity, and tunable fluorescence. The hydrogel is constructed via EDC/NHS-mediated grafting of terpyridine (TPY) onto polyethyleneimine (PEI), followed by freeze-thaw crosslinking. RE ions coordinate with TPY ligands to generate dynamic crosslinking sites, thereby reinforcing mechanical robustness while imparting strong luminescence. A salting-out effect induced by NaCl further densifies polymer chains and enhances ionic conductivity. Encapsulated with VHB elastomer, the hydrogel functions as an electrode in a triboelectric nanogenerator (RE-TENG), achieving a peak power density of 0.22 W m^-2. By directly coupling RE-doped fluorescent hydrogels with RE-TENGs, we demonstrate, for the first time, a fully self-powered and self-luminous hydrogel platform. The integrated device efficiently charges capacitors and drives UV LEDs to reveal encrypted fluorescent patterns without any external power supply. This work establishes a new paradigm for merging energy harvesting with information display, opening opportunities for next-generation wearable and secure optoelectronics.