Ensembles of Photonic Beads: Optical Properties and Enhanced Light-Matter Interactions

Light management is of paramount importance to improve the performance of optoelectronic devices including photodetectors, optical sensors, solar cells, and light-emitting diodes. Photonic crystals are shown as an effective metamaterial for trapping light among their various photon management functions. Herewith, it is demonstrated that spherical photonic crystals, or in other words, photonic beads, possess a stronger light-trapping effect compared to the planar counterpart. The photonic beads are fabricated by colloidal self-assembly under microdroplet confinement employing microfluidic devices. The light-matter interactions are illustrated by the emission intensity and lifetime of the embedded emitters, namely carbon dots and upconversion nanoparticles (UCNPs). The bandgaps of the photonic beads are selected according to the emission and excitation peaks of the light emitters, whereby the emission or excitation peak overlaps the blue edge or red edge of the photonic bands, respectively. Significantly stronger emission and extended luminescence lifetime are observed in photonic beads ensemble in comparison to the planar photonic crystals, demonstrating enhanced light trapping owing to the spherical geometry, which introduces additional microcavity effect. Photonic beads represent a perfect hierarchical light manipulation system. Combining both photonic and microcavity resonator effects, photonic beads potentially find applications in light harvesting, sensing, lighting devices, and light-triggered manipulations.