Disordered Particulate Media for Infrared Spectral Selectivity

Abstract

Selective control of infrared emission is typically achieved using ordered and periodic photonic structures, whose performance relies on precise fabrication and long-range structural coherence–severely limiting large-scale deployment. Here, these limitations are overcome by introducing a new class of disordered particulate materials with mid-infrared spectral selectivity, achieved by engineering the coupling between two distinct particle populations. The materials consist of silica particles that yield an absorption peak at 9 μm due to phonon resonances and lossless germanium particles. The latter particles provide a tunable scattering channel that balances radiative and absorptive losses in the system in order to activate critical coupling mechanisms, ultimately leading to a significant enhancement of the peak intensity. We experimentally demonstrate up to 70% absorption in subwavelength-thick layers, with numerical simulations identifying synthesis optimization as an effective strategy to further enhance this performance. Our approach integrates numerical design using the T-matrix method, fabrication of the selective material, X-ray nano-CT and scanning electron microscopy microstructural characterization, and experimental validation of the optical response via FTIR spectroscopy. These results establish disordered media as a competitive platform for achieving efficient and tunable spectral selectivity without relying on periodicity, providing a new framework for the design of functional thermal photonic materials.