Experimental observations of the simultaneous presence of a polaritonic and a photonic gap in a three-dimensional photonic crystal is reported, to the best of our knowledge, for the first time. The photonic crystal was made of monodispersed silica microspheres sedimented into a face-centered-cubic structure. Silica has a polaritonic gap for wavelengths between 8 and 9.35 (mu)m. Four different sphere sizes were used, with diameters of d velence 0.49, 0.73, 0.99, and 1.57 (mu)m. The photonic crystals were studied by normal incidence infrared reflectance measurements in the wavelength interval 0.8-12 (mu)m. Four peaks with the a magnitude of approx0.6, originating from the periodicity of the crystal, were recorded in the interval between 1 and 4 (mu)m. Another peak, the polaritonic reflectance peak (approx0.4), is observed for wavelengths around 9 (mu)m for all four crystals.
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