Excitation-Wavelength-Induced Dual-Band Fluorescence of Copper Halides for Multi-Mode Encryption and Anti-Counterfeiting Applications

Low-dimensional metal halides have emerged as promising anti-counterfeiting materials. However, achieving a multi-mode and multi-color anti-counterfeiting system in metal halides remains challenging. In this study, copper-halide (TBP)₂Cu₄Br₆ (TBP⁺ = C₁₆H₃₆P⁺) single crystals are synthesized using a cooling crystallization method, which exhibits efficient dual-band emissions (542 and 708 nm), large Stokes shifts (282 and 330 nm), and a high photoluminescence quantum yield (PLQY) of 92.7% for 542 nm. These exceptional properties are attributed to the unique 0D structure of (TBP)₂Cu₄Br₆ single crystals, which facilitates the formation of two different self-trapped excitons (STEs). Furthermore, based on (TBP)₂Cu₄Br₆, a multi-mode and multi-color digital anti-counterfeiting system integrated is designed with Morse code information encryption, demonstrating promising applications in information security and anti-counterfeiting. This work not only illustrates an emitter in copper halides but also paves the way for achieving multi-mode and multi-color anti-counterfeiting systems.