Chameleonic Color‐Variable Microbead Emitters for Multilevel Spectroscopic Encryption from Visible to Infrared Wavelengths

ABSTRACT Whispering‐gallery‐mode (WGM)‐mediated light emission produces sharp and distinct resonant peaks, providing a unique spectral signature that is ideal for photonic barcoding and compact microtagging. However, existing photonic barcodes are typically limited to visible wavelengths, restricting their tagging potential. Achieving precise light‐emission control across the entire Vis–near‐IR (NIR) spectral range is challenging, particularly when using a single object composed of a single material. Herein, multicolor‐emitting carbonized polymer microbeads (MECPMs) are synthesized on a gram scale by a facile and scalable hydrothermal process. These spherical microbeads, which contain extended π‐conjugated polycyclic aromatic hydrocarbons within their microcavities, emit broadband light spanning the entire Vis–NIR spectrum. Owing to their excitation‐dependent photoluminescence, a single MECPM can produce color‐tunable WGM‐based white‐light emission across the Vis–NIR spectrum, thereby enabling the generation of both visible and invisible microbarcodes by adjusting the excitation wavelength. Compared with conventional polymer‐ or oxide‐based microcavities, MECPMs demonstrate enhanced chemical stability in acids and organic solvents, excellent spectral tunability, and outstanding photonic encryption capabilities. Their environmentally friendly, metal‐free “chameleonic” photonic functionality provides a robust platform for anticounterfeiting, microtagging, labeling, and next‐generation photonic security systems. Additionally, this invention facilitates photonic encryption via information encoding and transmission across the Vis–NIR spectral range.