Quintuple-mode dynamic anti-counterfeiting using multi-mode persistent phosphors

Traditional luminescent inks used in anti-counterfeiting applications usually consist of single-mode photoluminescence (PL) or up-conversion luminescence (UCL) materials, which are mainly operated in single-level, monochromatic anti-counterfeiting and can be easily counterfeited. Here we report the achievement of quintuple-mode, multi-colour dynamic anti-counterfeiting using multi-mode Zn3Ga2GeO8:Cr3+,Yb3+,Er3+ and Zn1.6Li0.4GeO4:Mn2+ persistent phosphors as the luminescent inks. The Zn3Ga2GeO8:Cr3+,Yb3+,Er3+ phosphors exhibit quintuple luminescence modes of PL, persistent luminescence (PersL), photostimulated luminescence (PSL), photostimulated persistent luminescence (PSPL) and UCL with rich emission colours, while the Zn1.6Li0.4GeO4:Mn2+ phosphors possess quadruple luminescence modes of PL, PersL, PSL and PSPL with a long perceptible green afterglow. A 'dragonfly-on-lotus' pattern printed using these multi-mode persistent phosphors shows dynamic evolution of emission colours and brightness under different luminescence modes. The design strategy reported in this study may lead to the design and development of more sophisticated optical anti-counterfeiting technology.