Inverse photonic crystal films were prepared by photopolymerization of ethoxylate trimethylolpropane triacrylate (ETPTA) using opal-type templates. Their high quality was proved by investigations of structural and optical properties. The unexpectedly high refractive index, nETPTA ≈ 1.67, of polymerized ETPTA was obtained from a numerical approximation of the spectral positions of the reflectance peak of the films at different incidence angles. Fabricated samples were tested as sensors for water-ethanol mixtures, and a monotonous increase in the stop band shift with an increase in ethanol concentration was established.
Photonic crystals based on anodic aluminum oxide films are examined as refractive index sensors for controlling the composition of water-alcohol liquid mixtures. The position of the reflectance maximum corresponding to the first photonic stop band is used as the analytical signal. Impregnation of a photonic crystal with water-ethanol and water-glycerol mixtures results in a redshift of the reflectance maximum. A fairly high refractive index sensitivity, sufficient to determine the composition of water-ethanol and water-glycerol mixtures with an accuracy of about 1 wt.%, is observed. The detailed dependencies of the analytical signal on the composition of mixtures are experimentally investigated and compared with numerical calculations. Prospects and limitations of the refractive index sensors based on anodic alumina photonic crystals are discussed.
Inverse opal films impregnated with a methylene blue dye were prepared by a template route. Photonic stop band governs amplitude of spontaneous Raman scattering peaks for metal-free photonic crystals, enhancement factor being over 50.