Optical security: Tunable-resonator upconverted emission color printing

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.
Source: EurekaAlert, https://www.eurekalert.org