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 Zn_1.6Li_0.4GeO₄: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 Zn_1.6Li_0.4GeO₄: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.

To prevent counterfeiting, various luminescent anti-counterfeiting strategies, including multicolor, orthogonal, dynamic, and stimulus-response luminescence, are employed using long persistent phosphors.using long persistent phosphors.

Doping and varying pump laser parameters are the widely applied technological processes for tuning spectra to yield desirable luminescence properties and functions. For micro/nanocrystalline materials, doping is of fundamental importance in modifying electronic properties, modulating magnetism, as well as tuning the red-to-green luminescence ratio. Here we describe a tunable upconversion (UC) emission process in single NaYF₄:Yb/Er microtubes excitated with a focused laser. We show that the emission colours from single NaYF₄:Yb/Er microtubes can be rationally tuned in the red-to-green luminescence ratio and dynamics process by elevating Yb³⁺ ion concentration or pump power density. The underlying mechanism of spectral tuning is explored by using the power dependent UC luminescence, downconversion spectra and the temporal evolutions of UC emission from a series of single NaYF₄:Yb/Er microtubes. A mechanism of the red luminescence enhancement based on mediating electronic energy transfer channels by inducing three-photon processes is proposed for single microtubes. The natural decays of the luminescence levels are modified in the UC process relative to downconversion, which could be interpreted by using rate equations. Here, an insight into UC processes by use of unconventional focused experimental and theoretical techniques indicates the bidirectional feature of the electron transition of the interexcited-state by linear decays and UC processes via controlling external experimental parameters.

The ZGGO:Cr,Mn phosphors exhibit color-changeable photoluminescence and persistent luminescence via excitation wavelength and temperature management, showing the enormous potential for anti-counterfeiting and information storage applications.