Effect of pore-level geometry on far-field radiative properties of three-dimensionally ordered macroporous ceria...

The effects of pore size on direction-averaged radiative properties of three-dimensionally ordered macroporous (3DOM) cerium dioxide (ceria) particles are investigated in the spectral range of 0.3-10 μm. The particles are of spherical shape and contain interconnected pores in a face-centered cubic lattice arrangement. The porous particle is modeled as a three-dimensional array of interacting dipoles using the discrete dipole approximation (DDA). The validity of the Lorenz-Mie theory to predict far-field radiative properties of a quasi-homogeneous particle with the effective optical properties obtained using the volume-averaging theory (VAT) is demonstrated. Direction-averaged extinction, scattering, and absorption efficiency factors as well as the scattering asymmetry factor are determined as a function of the pore size for a particle of 1 μm diameter and as a function of the particle size for pores of 400 nm diameter. The overlapping ordered pores in the 3DOM particles and the boundary effects in the presence of pores of size comparable to that of the particle are shown to affect the radiative properties in the ultraviolet to near-infrared spectral ranges. The effects of the 3DOM pore-level features on the far-field radiative properties are not captured by the Lorenz-Mie theory combined with VAT. Consequently, the use of advanced modeling tools such as DDA is necessary. In the mid- and far-infrared spectral ranges, the effects of 3DOM pore-level features on the far-field radiative properties diminish and the approach combining the Lorenz-Mie theory and VAT is shown to be accurate.