Dual upconversion nanophotoswitch for security encoding

Light-harvesting lanthanide ions (Ln(3+)) doped NaYF4 inks could provide polychromatic patterns for opposing counterfeiting commodity infestation because of their distinctive upconversion photoluminescence (UPL) properties. Herein, three kinds of core-triple-shell Ln(3+) ions doped NaYF4 upconversion nanocrystals (UCNCs) are synthesized through modified high-temperature coprecipitation, which demonstrate excellent UPL properties of independent emitting colors under 808 or 980 nm laser excitation. Additive mixing three kinds of 808 nm emitted red-green-blue (RGB) UCNCs colloid solution can precisely regulate the emissions of the suspension for achieving full-color display. The as-obtained RGB three-primary colors induced by 808 nm laser accomplish broader color gamut than traditional standard RGB (sRGB) model and printing cyan-magenta-yellow (CMY) model. In addition, various China zodiac patterns and complex multicolor images are printed by the as-formulated UCNCs inks through screen printing technology. The printed patterns present colorful and polychromatic sequential toning visualization patterns under 808 nm excitation, while present another succession of gradually changed versatile patterns under 980 nm excitation. As a proof of concept, transparent polyvinyl chloride (PVC) self-adhesive anti-counterfeiting label is attached to the bottle of wine package for practical application. The demonstration of multiple model patterns of Chinese zodiac and poetry images based on these core-triple-shell UCNCs can be selected as a conceivable substitute of traditional single model patterns, underlining the full-color anti-counterfeiting level.