Core–Shell Structured Upconversion/Lead‐Free Perovskite Nanoparticles for Anticounterfeiting Applications

In view of their excellent luminescence properties, nanocrystalline metal halide perovskites have diverse optoelectronic applications, including those related to anticounterfeiting. However, high‐quality optical anticounterfeiting typically requires multiple encryptions relying on several optical modes to ensure information security. Herein, an efficient anticounterfeiting strategy based on dual optical encryption is realized by combining up‐ and downconversion luminescence in a nanocomposite with NaYF4 : Er3+,Yb3+ as core and a CsMnCl3 as shell. The emission color of this nanocomposite depends on the penetration depth of incident radiation and can be changed by varying the excitation source (980 nm laser or UV light) to produce different luminescent patterns. This feature allows one to effectively improve the anticounterfeiting index and fabricate professional anticounterfeiting materials. An up‐conversion nanoparticles and MnII‐based perovskite core–shell heterostructures nanocomposite was successfully synthesized for the first time, which showed dual‐color emissions under the excitation of UV light and IR laser. This work suggests its potential in high‐quality optical anticounterfeiting.