Lanthanide-Polyoxometalate-Based Film with Reversible Photochromism and Luminescent Switching Properties for Erasable Inkless Security Printing

Security printing is of the utmost importance in the information era. However, the excessive use of inks and paper still faces many economic and environmental issues. Thus, developing erasable inkless security printing materials is a remarkable strategy to save resources, protect the environment, and improve information security. To this endeavor, a photoresponsive lanthanide-polyoxometalate-doped gelatin film with high transparency was developed through the solution casting method. Attenuated total reflection Fourier-transform infrared spectroscopy confirmed the electrostatic and hydrogen bond interactions between gelatin and lanthanide-polyoxometalate. Absorption spectra, luminescent spectra, and digital images indicated that the film displayed reversible photochromism behavior and was accompanied by luminescent switching property upon exposure to UV irradiation and oxygen (in the dark) alternately, which allowed its potential application as a reprintable medium for inkless security printing. The printed information can be erased upon exposure to oxygen in the dark, and the film can be reused for printing again. The film exhibited excellent erasability, reprintability, renewability, and low toxicity. In addition, multiple encryption strategies were designed to improve information security. This work offers an attractive alternative strategy for constructing a reprintable film for inkless security printing in terms of simplifying the preparation process, saving resources, and protecting the environment.