Remarkable Enhancement of Upconversion Luminescence on Cap-Ag/PMMA Ordered Platform and Trademark Anticounterfeiting

High brightness of upconversion luminescence (UCL) for a thinner layer of UC nanoparticles is significant for routine applications of effective trademark anticounterfeiting technology. In this work, efficient UCL of NaYF₄:Yb³⁺,Er³⁺/Tm³⁺ was realized by combining a Ta₂O₅ dielectric layer on the cyclical island silver films supported by poly(methyl methacrylate) opal photonic crystals (PCs). The synergistic modulation of localized surface plasmon resonance and PC effect results in a significant improvement of the local electromagnetic field and an optimum UC enhancement of 145 folds. Furthermore, colorful pattern nanoprinting has been applied to this composite and used for trademark anticounterfeiting. The combination of angle-dependent PC effect and infrared-to-visible UCL represents a more advanced anticounterfeiting technique.