A Strong, Flexible, and Anticounterfeiting Fluorescent Composite Hydrogel from Carboxymethyl Cellulose-Eu(III) Cross-Linked Polyvinyl Alcohol

Fluorescent hydrogel as an advanced material has been used for anti-counterfeiting, probe detection, and optical devices. A facile strategy to prepare fluorescent hydrogel is developed by carboxymethyl cellulose (CMC) with Europium(III) and polyvinyl alcohol (PVA). The hydrogel forms a physical cross-linking network under mild reaction conditions without using volatile organic chemicals. The addition of CMC-Eu(III) improves the mechanical properties of the hydrogel. At 15% CMC-Eu(III), the hydrogel reaches its maximum tensile and compressive stress, which are 47.25 ± 10.35 and 10.14 ± 1.90 kPa, respectively. Meanwhile, the hydrogels exhibit a ⁵D₀→⁷F₂ characteristic emission peak assigned to Eu³⁺, which emits stable red fluorescence under 254 nm ultraviolet (UV) light. When this hydrogel is applied to paper, the paper showed hidden fluorescent dots under UV light. This additive also enhances the mechanical properties of the paper, which reveals the multifunctionality of this fluorescent hydrogel for anti-counterfeiting and reinforcement.