Carbon‐Based Photonic Microlabels Based on Fluorescent Nanographene‐Polystyrene Composites

Nanographenes (NGs) are attracting significant interest as atomically-thin carbon-based optical nanomaterials exhibiting a wide range of optical properties that are fine-tuned with ultimate atomic precision though chemical design. However, the use of NGs in photonic applications remains poorly explored. Here a straightforward procedure is demonstrated to load NGs onto the surface of polystyrene microbeads in order to synthesize a functional light emitting microcomposite. The resulting all-carbon-based microbeads behave as optical microresonators displaying narrowband emission lines spread across the whole visible spectrum. The unique fluorescent pattern of individual microbeads enables applications in metrology and information encoding. This is shown, as a proof-of-concept, by absolute diameter and refractive index estimates of individual polystyrene microbeads with nanometric precision, and the design of an unclonable photonic microtag for anti-counterfeiting applications. These results pave the way to a new family of carbon-based microdevices with a wide range of applications in photonics.