Tunable Optical Properties and Enhanced Stability of Organic-Inorganic Hybrid Cu-Based Halide Thin Films for Advanced Anti-Counterfeiting Applications

The development of highly stable and optically tunable materials is crucial for next-generation patterning and anti-counterfeiting applications. This study presents a comprehensive investigation into the synthesis, structural dynamics, and optoelectronic properties of MA 4 Cu 2 X 6 (X = Cl, Br, Br/Cl) films fabricated via a three-step spin-coating technique. By leveraging halide anion engineering, the precise control over the coordination environment of Cu centers are achieved, as evidenced by synchrotron-based extended X-ray absorption fine structure analysis. Both their strong electron–phonon coupling and high exciton binding energies facilitate efficient self-trapped exciton emission. The photoluminescence emission is tailored from yellow to green and eventually to blue-green under ultraviolet excitation (254 nm). STE localization mitigates thermal quenching, achieving PLQYs >64%. Stability assessments indicate that mixed-halide compositions effectively suppress Cu+ oxidation, prolonging luminescence performance. Mixed halides enhance environmental stability, retaining >25% initial PLQY after 720 h in ambient conditions. Furthermore, the films demonstrate tunable diffraction properties in patterned photonic architectures, highlighting their potential for advanced optoelectronic devices. The films demonstrate high-resolution patterning capabilities via photolithography and screen printing, underscoring their potential for advanced optical security applications.