Color-tunable luminescent hydrogels assembled by sodium alginate/κ-carrageenan via rare-earth ion coordination for information encryption

Color-tunable luminescent hydrogels were assembled from naturally derived sodium alginate (AG) and κ-carrageenan (κ-Car). • The hydrogels were formed through coordination interaction between Eu 3+ /Tb 3+ ions and the carboxylate groups of AG, together with a 3D hydrogen-bonding network. • The hydrogel beads and films were fabricated by the droplet method and the immersion/ion diffusion method, respectively. To develop biocompatible optical materials with high transparency, tunable emission, and information encryption capability, color-tunable luminescent hydrogels were prepared using naturally derived sodium alginate (AG) and κ-carrageenan (κ-Car) as a composite polysaccharide matrix. The hydrogels were formed through coordination interaction between Eu 3+ /Tb 3+ ions and the carboxylate groups of AG, together with a three-dimensional hydrogen-bonding network from AG and κ-Car. 2,6-Pyridinedicarboxylic acid (DPA) was introduced as an antenna ligand to sensitize the characteristic emission of rare-earth ions. Luminescent hydrogel beads and films were fabricated by the droplet method and the immersion/ion diffusion method, respectively, and then their photoluminescence properties, microstructures, and information encryption behaviors were systematically investigated. The obtained hydrogels remained highly transparent under visible light and exhibited intense emission under UV excitation. DPA markedly enhanced the characteristic emission of Eu 3+ , and continuous color tuning from red to green was achieved by varying the Eu 3+ /Tb 3+ molar ratio. SEM and FT-IR analyses revealed that the hydrogel films possessed a layered microstructure and that carboxylate groups were involved in coordination with rare-earth ions. Taking advantage of the optical feature of being hidden under visible light and revealed under UV light, array-based and multilevel responsive information encryption models were constructed, enabling the visual readout of concealed information. This work provides a facile and environmentally benign strategy for constructing rare-earth luminescent hydrogels and expands their potential applications in anti-counterfeiting and information encryption. Color-tunable luminescent hydrogels for information encryption were assembled from naturally derived sodium alginate (AG) and κ-carrageenan (κ-Car) via Eu 3+ /Tb 3+ ions coordination, sensitized by 2,6-pyridinedicarboxylic acid (DPA). The hydrogel beads and films were fabricated by the droplet method and the immersion/ion diffusion method, respectively. Download: Download high-res image (113KB) Download: Download full-size image