Laser‐Induced Dehalogenation for Direct Writing Stable, Thermally Robust Patterned Arrays of Lead Halide Perovskite Nanocrystals

ABSTRACT Laser direct writing (LDW) offers a powerful, mask‐free, and straightforward route for fabricating high‐resolution, luminescent microarrays of lead halide perovskite nanocrystals (LH PNCs) within polymer films. However, when prepared from conventional halide salt precursors, the low intrinsic formation energy of ionic LH PNCs renders them highly susceptible to thermally induced erasing, severely limiting their practical utility. To overcome this limitation, we introduce halogenated organic compounds (R‐X) as the halogen source. Irradiation with a high photon energy 355 nm nanosecond laser directly cleaves the C─X bond, releasing halide anions that initiate the in situ nucleation and growth of LH PNCs within the polymer matrix. This strategy enables the rapid fabrication of multicolour luminescent LH PQD microarrays across a broad range of polymer substrates, while effectively suppressing thermal erasing that they retain their structural integrity even after heating to 120°C, whereas analogous microarrays fabricated from halide salts erased at only 50°C. Leveraging this exceptional stability together with the design versatility of LDW, we further demonstrate the creation of mesoscopic fluorescent anti‐counterfeiting labels such as those embedded in express packaging, highlighting the potential for scalable, secure, and multifunctional photonic applications.