Thermal emission from agglomerated polaritonic dielectric particles

This work investigates the impact of particle agglomeration on thermal emission from polaritonic dielectric particles supporting localized surface phonons (LSPhs) in the infrared. Specifically, the spectral, hemispherical emissivity from 50- and 500-nm-radius $\mathrm{Si}{\mathrm{O}}_{2}$ particle chains is predicted via the discrete system Green's function method based on fluctuational electrodynamics. It is shown that contacting and near-contacting particles support collective LSPhs (cLSPhs) that cause significant spectral broadening and resonance damping of the emissivity. cLSPhs, arising from the coupling of LSPhs between closely spaced particles, can travel across particle chains. The dipolar contribution to the cLSPh dispersion relations reveals that the resonance damping and spectral broadening are mediated by long-range cLSPh modes in longitudinal polarization. These modes contribute to thermal emission when the particle edge-to-edge spacing to radius ratio, $d/R$, is smaller than approximately 1 and 4 for particle radii of 50 and 500 nm, respectively. Beyond these thresholds, LSPh coupling between particles is negligible, and thermal emission from multiple particles becomes additive. These findings have implications for manufacturing dielectric-based metasurfaces and metamaterials used for controlling thermal emission in energy conversion and thermal management systems.