Spin-coating (C4H10N)4Cu4I8 fluorescent film for anti-counterfeiting

This study reports the successful fabrication of (C 4 H 10 N) 4 Cu 4 I 8 (PCI) thin films via a facile spin-coating method, establishing a solution-processable route for high-performance luminescent materials. These films exhibit exceptionally broad optical characteristics, including broad excitation (260 nm) and emission bandwidths (300 nm), alongside a large Stokes shift of 310 nm. Bimodal fitting of the photoluminescence spectrum reveals a dual-emission mechanism with peaks at 541 nm (Peak-I) and 598 nm (Peak-II). Density functional theory (DFT) calculations attribute the broad spectra to enhanced lattice-electron coupling and self-trapped excitons (STEs) derived from the [Cu 4 I 8 ] 4- clusters. DFT calculations yield a narrow bandgap of 2.08 eV, consistent with the assignment of Peak-II to the [Cu 4 I 8 ] 4- and [C 4 H 10 N] + ionic clusters. Structural analyses confirm the films' dendritic morphology and high crystallinity, while thermal analysis demonstrates robust stability up to ∼330 °C. Significantly, proof-of-concept applications in planar light sources and screen-printed anti-counterfeiting highlight the material's potential for next-generation optoelectronic devices.