Nanoparticles of TiO 2 and VO 2 in dielectric media: Conditions for low optical scattering, and comparison between effective medium and four-flux theories

Abstract

Spectral transmittance and reflectance in the 300 to 2500 nm solar-optical wavelength range were calculated for nanoparticles of titanium dioxide and vanadium dioxide with radii between 5 and 100 nm embedded in transparent dielectric media. Both of the materials are of large importance in green nanotechnologies: thus TiO 2 is a photocatalyst that can be applied as a porous film or a nanoparticle composite on indoor or outdoor surfaces for environmental remediation, and VO 2 is a thermochromic material with applications to energy-efficient fenestration. The optical properties, including scattering, of the nanoparticle composites were computed from the Maxwell-Garnett effective-medium theory as well as from a four-flux radiative transfer model. Predictions from these theories approach one another in the limit of small particles and in the absence of optical interference. Effects of light scattering can be modeled only by the four-flux theory, though. We found that nanoparticle radii should be less than ~20 nm in order to avoid pronounced light scattering.

Numerical Characterization of Vanadium Dioxide Thin Films Applied to Thermal Building Insulation: Determination of Dielectric Constant Using PSO Algorithm

“…This method of optimization gives us some interesting results ( fig.3, 4, 5), compared to the experimental results given by Kakiuchida et al [13,14] and C.G. Granqvist et al [6], our results are in good agreement and show a high similarity with an average error of about 7,5% with experimental ones. We can observe in figure 4 and 5 some distortions in the curves near 1500 nm.…”

“…The second limitation is related to high absorption in the visible part of solar spectrum, this phenomenon was noticed experimentally by C.G. Granqvist et al [6] and Y. Gao et al [7], and numerically O. Iken et al [8] using the kubelka Munk method.The study of thermo-chromic properties of VO 2 requires data of optical constants (refractive index n (T, λ) and extinction coefficient k (T, λ)) for different temperatures above and under transition. The determination of those two properties is purely experimental, thus it requires simple fabrication and characterization by ellipsometry [9].…”

“…The second limitation is related to high absorption in the visible part of solar spectrum, this phenomenon was noticed experimentally by C.G. Granqvist et al [6] and Y. Gao et al [7], and numerically O. Iken et al [8] using the kubelka Munk method.…”

Thermochromic light scattering from particulate VO2 layers

“…26 Such particles can be prepared by many different techniques, as surveyed in earlier papers. 10,12 Here we use reactive DC magnetron sputtering, which has been found capable of making TC nanorods and nanoparticles.…”

Multilayer four-flux matrix model accounting for directional-diffuse light transfers

“…Recent formulations [22,23] also enable predicting interface effects. The four-flux model can be used for various scattering systems as illustrated by recent publications [24][25][26][27]. However, even if the fourflux approach is much easier to use than more elaborated models, the simplicity of the two-flux approximation is still often preferred.…”