Anticounterfeiting Labels with Smartphone-Readable Dynamic Luminescent Patterns Based on Tailored Persistent Lifetimes in Gd2O2S:Eu3+/Ti4+

Abstract

Dynamic luminescent labels, in which a luminescent image changes with time after ultraviolet excitation is turned off, are attractive for anticounterfeiting. A sequence of Gd2O2S:Eu3+/Ti4+ phosphors is presented in which the Ti4+ doping concentration allows the persistent emission lifetime to be varied from 1.17 ± 0.02 to 5.95 ± 0.07 s. While this persistent lifetime is tuned, the photoluminescence quantum yield remains over 46% ± 3%. A broad charge-transfer band allows these phosphors to be excited with inexpensive and relatively safe 375 nm light-emitting diodes. By developing patterns with phosphors that have differing persistent lifetimes, dynamic changes in the luminescent image after the excitation source is removed can be observed. For patterns made from phosphor materials that have big differences in persistent lifetimes, these dynamic changes are observable by the eye. By contrast, the dynamic changes in patterns made by phosphors with comparable persistent lifetimes (0.20 s delayed lifetime difference) are difficult to observe by the naked eye but can be easily determined by analysis of a 30-frames-per-second video taken with a smartphone. Thus, these bright phosphors with tunable persistent lifetime allow both overt (observable by eye) and covert (requiring smartphone video analysis) dynamic anticounterfeiting labels to be created.