A flexible, long afterglow film with Bi-activated garnet phosphors for dynamic anti-counterfeiting applications

Fluorescent materials have been widely used in the field of anti-counterfeiting, but traditional fluorescent patterns are static by design, which only offer a limited level of security for anti-counterfeiting encryption. Herein, we provide a novel dynamic anti-counterfeiting strategy by constructing a flexible, long afterglow film with Bi-activated Sr 3 Y 2 Ge 3 O 12 phosphors. Theoretical calculation indicates that the Sr 3 Y 2 Ge 3 O 12 garnet matrix with suitable energy bands shows high adaptability for Bi ions activator to produce long afterglow emission. Doping of Bi ions into the framework of Sr 3 Y 2 Ge 3 O 12 exhibits a blue luminescence centered around 469 nm. The afterglow intensity and decay time reach the optimal with Bi 3+ doping concentration of 0.75 mol%. Various characterizations show that the electron traps mainly come from oxygen vacancies in the long afterglow process, and a possible afterglow mechanism is also proposed. A flexible, long afterglow film prepared by compositing with Sr 3 Y 2 Ge 3 O 12 :Bi 3+ can be written into the image information by ultraviolet light and present a dynamic image in the form of afterglow. The information decryption could be further performed by thermal excitation. The results illustrate that the Bi-activated Sr 3 Y 2 Ge 3 O 12 flexible film is a potential luminescent material that can be used for dynamic anti-counterfeiting and encryption.