Triple-Level Information Encryption Enabled by Fluorescent Microspheres: Harnessing Structural Color, Fluorescence,...

The growing demand for anticounterfeiting of high-value goods calls for advanced technologies that integrate multiple security features. Here, we demonstrate a triple-information encryption system based on fluorescent microspheres. Monodisperse polystyrene fluorescent microspheres doped with the rare-earth complex Eu(TTA)₃(TOPO)₂ were synthesized via emulsion polymerization, achieving tunable diameters (132-288 nm) and intense red emission at 612 nm. By optimizing the rheological properties of the colloidal ink and precisely controlling the electrohydrodynamic printing process, high-quality full-color structural color patterns were fabricated. Crucially, by exploiting the Purcell effect of the photonic crystal, we engineered a spatially graded fluorescence enhancement across the patterns, thereby establishing the triple-encryption mechanism. The resulting patterns exhibit angle-dependent structural colors under ambient light, switch to uniform red fluorescence under UV illumination, and conceal a microscopic fluorescence intensity gradient that acts as a unique "spectral key" for authentication. This work offers a cost-effective strategy for high-security dynamic anticounterfeiting.