In situ doped Cs₂AgIn_0.9Bi_0.1Cl₆:8%Yb,2%Er/PVDF composite films for the printing of multimodal fluorescent anti-counterfeiting marks

The fluorescent anti-counterfeiting technology has become one of the most desirable candidates in practical anti-counterfeiting applications owing to its adjustable emission, high recognition and design flexibility. However, the security level of single emitting fluorescent materials was lower, and no longer able to cope with current forgery techniques, so the development of higher level multimodal fluorescent anti-counterfeiting technologies was urgent. In this report, lead-free double perovskite (DP) material CsAgBiCl₆ was chosen as the host and a technique for in situ growth in polymer polyvinylidene difluoride (PVDF) was proposed to obtain large-scale high-quality Cs₂AgBiCl₆/PVDF composite films (CFs). Subsequently, the Cs₂AgIn_0.9Bi_0.1Cl₆:8%Yb,2%Er/PVDF CFs with both down-conversion and up-conversion optical properties was achieved by hybrid (In³⁺/Yb³⁺/Er³⁺) doping, which was able to displayed inconsistent fluorescence emission (orange and green) under different excitation sources, and their fluorescence intensities exhibited tunability with the change of the environmental temperature, greatly enhancing its competitiveness in the field of fluorescent anti-counterfeiting. Finally, different anti-counterfeiting marks have been designed by the screen-printing process, and the complex encryption once again ensured the security of the information, while bringing a new gospel to the subsequent development of lead-free DP materials.