All-Inorganic Sb-Doped Cs₃MnCl₅ Nanocrystals Enable Multi-Codon Visible Emissions via Coupled Multiexcitonic Processes for Advanced Optical Encryption

Luminescent metal halides have garnered significant attention for next-generation optoelectronic applications, particularly in information encryption, due to their excellent optical properties and ease of solution-based processing. In this study, we present Sb-doped Cs3MnCl5 nanocrystals (NCs) as a highly promising candidate for advanced information security applications. For the first time, we successfully synthesized these NCs with a high photoluminescence quantum yield (∼80%) using a hot-injection method. By doping with Sb3+ ions, we expanded the emission spectrum across the visible range─from green to red light, including yellow-green, orange, and orange-red─enabling unprecedented spectral modulation in manganese-based metal halide perovskites. Through spectral analysis and density functional theory (DFT) computations, it is found that the 525 nm emission arises from the d–d transition of Mn2+ ions in a tetrahedral coordination environment, while the 660 nm emission is attributed to self-trapped excitons from Sb3+ ions, facilitated by energy transfer from Mn–Mn d–d transitions. This mechanism differs from previously reported decoupled multiexcitonic luminescence in Sb3+ doped perovskite materials, enabling more efficient tuning of the relative intensity between the dual emissions through variation in dopant concentrations and excitation wavelengths. Furthermore, Sb3+ doping enables excitation wavelength-dependent emissions, allowing for the generation of multiple codons with distinct variations at different concentrations. This tunable emission capability proves highly effective for encrypting multilevel optical codes, offering significant advantages over conventional anticounterfeiting materials. Our findings provide valuable insights for designing low-toxicity, high-efficiency perovskites with tunable emission properties for practical information security applications.