Triple-Level Information Encryption Enabled by Fluorescent Microspheres: Harnessing Structural Color, Fluorescence, and Purcell-Effect Spectral Key

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.