Rare‐Earth‐Metal‐Free Solid‐State Fluorescent Carbonized‐Polymer Microspheres for Unclonable Anti‐Counterfeit Whispering‐Gallery Emissions from Red to Near‐Infrared Wavelengths

Abstract

AbstractColloidal carbon dots (CDs) have garnered much attention as metal‐free photoluminescent nanomaterials, yet creation of solid‐state fluorescent (SSF) materials emitting in the deep red (DR) to near‐infrared (NIR) range poses a significant challenge with practical implications. To address this challenge and to engineer photonic functionalities, a micro‐resonator architecture is developed using carbonized polymer microspheres (CPMs), evolved from conventional colloidal nanodots. Gram‐scale production of CPMs utilizes controlled microscopic phase separation facilitated by natural peptide cross‐linking during hydrothermal processing. The resulting microstructure effectively suppresses aggregation‐induced quenching (AIQ), enabling strong solid‐state light emission. Both experimental and theoretical analysis support a role for extended π‐conjugated polycyclic aromatic hydrocarbons (PAHs) trapped within these microstructures, which exhibit a progressive red shift in light absorption/emission toward the NIR range. Moreover, the highly spherical shape of CPMs endows them with innate photonic functionalities in combination with their intrinsic CD‐based attributes. Harnessing their excitation wavelength‐dependent photoluminescent (PL) property, a single CPM exhibits whispering‐gallery modes (WGMs) that are emission‐tunable from the DR to the NIR. This type of newly developed microresonator can serve as, for example, unclonable anti‐counterfeiting labels. This innovative cross‐cutting approach, combining photonics and chemistry, offers robust, bottom‐up, built‐in photonic functionality with diverse NIR applications.