Thermal radiation properties, such as reflectivity and emissivity, have been well modified by using a photonic crystal in this decade. In this paper we fabricated three-dimensional photonic crystals by self-assembled silica particles with 3μm diameter. The close-packed hexagonal photonic crystal with defects is observed by SEM. The measured specular reflectance explained by modified Bragg's law is measured with a diffuse reflectance by FT-IR. The near normally incident diffuse reflectance is measured by using paraboloidal mirrors to understand the diffuse reflection. We experimentally confirmed the strong diffuse reflectance in the near infrared regions. We numerically calculated reflectance of the three-dimensional photonic crystals by RCWA. The diffuse reflectance in near infrared is calculated only in the photonic crystal with defects. The numerically calculated diffuse reflectance is roughly explained by Mie scattering theory. The directional emissivity of the photonic crystal is measured by FT-IR with collimator. The normal emittance is suppressed in the photonic gap, but the directional emittance is enhanced in 30 degrees. The absorptance is numerically calculated to understand the experimental results. The numerical results show that the directional absorptance is increased in narrow direction. The directional sharp peak in 30 degrees is calculated although the monocrystalline photonic crystal is assumed in the numerical model. The effects of the defects in the photonic crystal on the emittance should be considered to explain the experimental results.
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