Multi-wavelength excitation-dependent fluorescence with dynamic color gradients for information encryption and anti-counterfeiting

Abstract

Developing optical anti-counterfeiting technology with dynamic color changes offers new hope for improving the replication difficulty of anti-counterfeiting labels and promoting the updating and iteration of high-level security technology and information encryption, but remains a huge challenge. Herein, we develop a ground-breaking multi-wavelength excitation-dependent anti-counterfeiting technology based on security inks containing three luminescent materials that respond to 254 nm, 365 nm, and 980 nm excitation, respectively. A blue carbon dots/calcium carbonate (B-CDs/CaCO₃) composite and a green carbon dots/silicon dioxide (G-CDs/SiO₂) composite are prepared via in situ loading processes. The former exhibits blue fluorescence (FL) emission light and green room-temperature phosphorescence (RTP) when turning on/off 365 nm excitation, and the latter emits green FL under the same conditions. Under 254 nm excitation, excellent red emission is realized in the YVO₄:Eu³⁺ (R-Eu) phosphor. Blue and green upconversion luminescence (UCL) are obtained in YVO₄:Tm³⁺/Yb³⁺ and YVO₄:Er³⁺/Yb³⁺ phosphors upon 980 nm excitation. When integrating these luminescent materials into invisible security inks, the printed security patterns exhibit triple-mode polychromatic information and spatial dynamic color-gradient characteristics by varying the excitation conditions (wavelength, intensity, illumination angle, and exposure time of excitation light). The unique optical properties enable the resulting security labels to show a high-level anti-counterfeiting strength and demonstrate application value in next-generation anti-counterfeiting.