Mechanistic Insights Into Anti‐Kasha, Persistent, and Self‐Trapped Emission in (C ₆ H ₁₆ N ₂ ) ₂ InCl ₇ :Sb ³⁺ Hybrids for Multi‐Level Anti‐Counterfeiting Application

Abstract The escalating prevalence of counterfeit products has fueled the urgent demand for advanced anti‐counterfeiting materials with multi‐dimensional security features. In this study, the design and synthesis of a novel class of organic‐inorganic hybrid metal halides (OIHMHs), specifically (C 6 H 16 N 2 ) 2 InCl 7 (CIC) and its Sb 3+ ‐doped derivatives are presented. These materials uniquely integrate anti‐Kasha emission, persistent luminescence, and self‐trapped excitons (STEs) emission. The CIC material exhibits blue and cyan emissions under varying UV excitations, accompanied by a 3‐s cyan persistent luminescence. Strategic doping of Sb 3+ introduces yellow STEs emission, enabling color tuning from cyan to white and yellow. Advanced computational analyses, including density functional theory (DFT) and defect formation energy calculations, uncover the origins of these emissions. The anti‐Kasha behavior is attributed to π‐π* transitions of the organic cation, while the persistent luminescence arises from Cl vacancy ( V Cl ) defects acting as energy storage traps. Leveraging these optical properties, a sophisticated binary coding system with six layers of anti‐counterfeiting security and CIC:5%Sb 3+ @SEBS composite film with outstanding spatial resolution have been developed. This work not only provides new research directions for prompt and delayed luminescence tuning in OIHMHs but also establishes a robust theoretical foundation for anti‐counterfeiting and information encryption fields.