Visible and near-infrared emission of lead-free Cs3Cu2I5:Bi perovskite by valence state regulation for optical anti-counterfeiting coatings

In recent years, the proliferation of counterfeit products has led to increased concerns about anti-counterfeiting technology, with traditional single-mode fluorescence methods proving insufficient due to their susceptibility to replication. The new copper-based halide materials have shown great potential in the field of multi-mode anti-counterfeiting due to their unique structure, excellent luminescence performance, and high defect tolerance. In this work, near-infrared emission of Cs₃Cu₂I₅ was achieved for the first time through Bi doping. By exploiting the dual emission center characteristics of the resulting Cs₃Cu₂I₅:Bi, we demonstrated its excitation wavelength-dependent emission. It was then mixed with cyclohexane to prepare an advanced fluorescent anti-counterfeiting coating for screen printing, enabling high-precision pattern printing onto various substrates. The resulting anti-counterfeiting patterns exhibit excellent weather resistance, remaining virtually unchanged after 60 days at room temperature. This study lays the foundation for expanding the emission range of Cs₃Cu₂I₅ and adjusting multi band emission, and confirms its potential application in the field of multi-mode anti-counterfeiting.