Fingerprint visualization and anti-counterfeiting applications using lead-free Cs₃Cu₂Cl₅ perovskite via a facile green synthesis

Latent fingerprint visualization is significant for personal identification and forensic investigation. However, the traditional methods suffer from high toxicity, low contrast, complicated preparation, and poor universality. In this work, we developed a green synthesis method for nontoxic lead-free Cs₃Cu₂Cl₅ microcrystals, employing oleic acid (OA) as a passivating agent and ethanol as an anti-solvent. The synthesized Cs₃Cu₂Cl₅-OA microcrystals exhibit excellent properties, such as high green fluorescence with a peak at 535 nm. The broadband fluorescence is attributed to self-trapped exciton (STE) emission, as indicated by the excitation-dependent photoluminescence (PL) spectra. Leveraging the electrostatic interactions between fingerprint oil deposits and the surface ligands of Cs₃Cu₂Cl₅, we innovatively applied the Cs₃Cu₂Cl₅-OA powder for latent fingerprint identification, demonstrating reliability and applicability. Additionally, the Cs₃Cu₂Cl₅-OA was successfully used to create a fluorescent anti-counterfeiting pattern on filter paper. This work underscores the potential of eco-friendly Cs₃Cu₂Cl₅-OA microcrystals as promising fluorescent agents for both latent fingerprint visualization and anti-counterfeiting applications in forensic and security fields.