Comprehensive Summary Advanced fluorescent anti‐counterfeiting technologies have garnered widespread attention due to the insufficient security of traditional anti‐counterfeiting methods. Addressing the ongoing demand for more secure anti‐counterfeiting methods, we pioneered a simple and effective strategy for the on‐demand fabrication of CsPbBr₃ nanocrystalline patterns via direct laser writing on CsPbBr₁.₈I₁.₂ perovskite thin films. The resulting films were comprehensively characterized in terms of morphology, structure, elemental composition, and optical properties. Our investigation reveals that mild laser irradiation induces a reaction between iodide ions and ambient oxygen, leading to iodide depletion and local bromide enrichment with replacing the lattice positions of these iodide vacancies. This halide exchange facilitates the formation of CsPbBr₃ nanocrystals, which exhibit bright green luminescence under 365 nm UV excitation. At higher laser intensities, blue luminescence can also be achieved, attributed to the smaller crystal sizes. By leveraging programmable design, we successfully generate green‐ and dual‐emissive patterns within otherwise non‐luminescent CsPbBr₁.₈I₁.₂ films, offering a promising route for optical anti‐counterfeiting applications. This work demonstrates a novel, laser‐assisted technique for the controlled creation of fluorescent security features.
Jin et al. (Wed,) studied this question.