Scientists have demonstrated a new optical security element that not only combines microprints with invisible inks, but also makes them colorful. This is done using a single type of material for the ink, and another for the microprint. This so-called tunable resonator?upconverted emission (TRUE) color printing is demonstrated by embedding a monolayer of nanocrystals in close proximity with aluminum nanostructures. Multiple luminescent and plasmonic colors are simultaneously utilized to incorporate different covert luminescent information within an ultrahigh resolution plasmonic color print.
