Generated White Light Having Adaptable Chromaticity and Emission, Using Spectrally Reconfigurable Microcavities.

Metal-free, luminescent, carbogenic nanomaterials (LCNMs) constitute a novel class of optical materials with low environmental impact. LCNMs, e.g., carbon dots (CDs), graphitic carbon nitride (g-CN), and carbonized polymer microspheres (CPM) show strong blue/cyan emissions, but rather weak yellow/red emission. This has been a serious drawback in applying them to light-emitting and bio-imaging applications. Here, by integrating single-component LCNMs in photonic microcavities, the study spectroscopically engineers the coupling between photonic modes in these microcavities and optical transitions to "reconfigure" the emission spectra of these luminescent materials. Resonant photons are confined in the microcavity, which allows selective re-excitation of phosphors to effectively emit down-converted photons. The down-converted photons re-excite the phosphors and are multiply recycled, leading to enhanced yellow/red emissions and resulting in white-light emission (WLE). Furthermore, by adjusting photonic stop bands of microcavity components, color adaptable (cool, pure, and warm) WLE is flexibly generated, which precisely follows the black-body Planckian locus in the chromaticity diagram. The proposed approach offers practical low-cost chromaticity-adjustable WLE from single-component, luminescent materials without any chemical or surface modification, or elaborate machinery and processing, paving the way for practical WLE devices.