Tailoring luminescent patterns with rare-earth photonic materials for anti-counterfeiting applications: A lightkey

Abstract

Anti-counterfeiting strategies are competitively developed against fast-growing counterfeit markets as a cornerstone for the next generation of luminescent security inks, so it will be more difficult to mimic by ever increasing sophisticated counterfeiters. In particular, rare-earth doped up-conversion luminescent materials present important advantages such as invisibility in ambient light, excitation by low cost NIR irradiation, lack in background noise and negligible auto-fluorescence from the surface. Here we present colour tuneable up-conversion emissions in two families of rare-earth doped photonic materials (sol-gel derived nano-glass-ceramics and glasses prepared by melt quenching technique) for tailoring the overall emitted luminescence, as a sort of “lightkey”. In particular, intensity ratios among UV and VIS up-conversion emission bands can be tuned by modifying doping concentration level and excitation power density, as an additional security feature itself, giving rise to a multi-digit security code based on light-responsive encrypted patterns.