Highly efficient, stable and bright blue phosphorescent ink to prevent counterfeit of currency and merchandise barcodes

Abstract In the current work, a distinct class of Ca 0.87 Al 2 O 4 : 0.01Eu 2+ , 0.02Nd 3+ , 0.1Si 4+ long afterglow phosphor powder was synthesized using high-temperature (1000–1500 °C) solid-state reaction method followed by formulation of an ink using epoxy based colloidal suspension. Interestingly the ink absorbs invisible energies either from D65 light and/or ultraviolet (∼365 nm) light, stores up the energy and emit as bright blue (∼450 nm) photoluminescence (PL) apparently visible for >4 h for dark adapted human eyes. Furthermore, the phenomenon of long (>4 h) afterglow allows us to create/design unique concealed patterns on goods and certificates using quick response (QR) code patterns. Systematic experiments have been carried out in a dark chamber on different models held a few seconds under UV (∼365 nm) excitation to distinguish fake merchandise products, barcodes and prevent counterfeit of currency as well as excessive UV radiation exposure for longer periods of time.