Monodisperse PMMA beads of a size varying between 200 and 400 nm have been prepared by a modified emulsion polymerization technique. These beads sediment well on substrates to form 3-dimensional face-centered cubic packages. This method allows it to cover large glass substrates (area up to 10 × 10 cm) with an opalescent layer of the beads thus creating films with opaline structure, which can be used as photonic crystals. Choosing PMMA as the material of the beads brings several advantages, e.g., the PMMA photonic films can be precisely patterned by e-beam lithography with the feature resolution down to one bead in width and various fluorescent dyes can be incorporated in PMMA balls. Dye-impregnated PMMA opaline photonic films demonstrate the incomplete photonic band gap structure and related modification of dye photoluminescence spectrum.
Photonic crystals in the form of large area thin films consisting of closely packed polymethylmethacrylate beads were sedimented on glass substrates. The high ordering of the opaline films made it possible to observe a number of fine features in the optical diffraction, including Fabry-Perot oscillations of the reflectivity and branching of the angular dispersion of the Bragg resonances with increase of the angle of incidence of the light beam. Results of calculations of the photonic band structure and simulations of the reflectance spectra agree well with experimental observations.
The photoluminescence of a dye embedded in the three-dimensional SnS2 inverted opal has been studied. Changes of the emission spectrum compared with the free-space dye emission was observed in the stop-band frequency range in accord with reflectance/transmission spectra of this photonic crystal. The angular-dependent component, due to the Bragg stop band, and the angular-independent component, which is, possibly, related to the minimum in the density of photon states, have been distinguished in the dye emission spectrum.
Large‐area inverted photonic crystals of SnS2 are prepared here by infilling poly(methylmethacrylate) (PMMA) opaline thin films with SnS2 by chemical vapor deposition. Dissolution of the polymer beads leaves a large inverted replica with good optical properties (see Figure), owing to the high bulk refractive index and wide electronic gap of the material.
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