We report on the optical properties of polystyrene opals infiltrated with solutions of ad hoc synthesized heteroaromatic quadrupolar dyes endowed with strong nonlinear optical properties (two-photon absorption). Transmittance spectroscopy of opals infiltrated with dye water solutions shows both a bathochromic shift and a reduced width of the photonic crystal stop band. Moreover, variable angle transmittance spectra highlight the high energy dispersion of the stop band upon increasing the incidence angle. Photoluminescence spectra recorded at different emission angles with respect to the normal of the sample for such infiltrated opals show that the emission spectrum is strongly modified at the stop band according to the opal dispersion properties. A careful comparison of the intensity and spectral properties of photoluminescence in opals possessing a properly tuned photonic stop band is reported and discussed. Two different effects are observed: when concentrated solutions are used, emitted light filtering due to the photonic stop band is observed. On the other hand, by properly reducing solution self-absorption, directional enhancement of emission in the high energy side of the stop band is observed. Physical mechanisms responsible for this phenomenon are discussed.

A seeded surfactant‐free methyl methacrylate emulsion polymerization is employed to prepare core–shell particles with predetermined size and narrow size distribution. The particle size is determined by the ratio between methyl methacrylate (MMA, shell) and polytetrafluoroethylene (PTFE, core). Monodisperse particles in the 100–350 nm range are obtained. These particles are used to grow colloidal photonic crystals (opals) of very high optical quality, thus indirectly demonstrating the excellent control of microbead size distribution achieved by this preparation technique. The optical properties of the opals are investigated by means of reflectance and polarized‐angle‐resolved transmittance spectroscopies. These data provide a rough determination of the effective refractive index of the system, which is favorably compared with values obtained by simple effective medium models. Copyright © 2012 Society of Chemical Industry

In this work, we report on the optical properties and amplified spontaneous emissions (ASE) of polystyrene opals engineered with planar structural defects containing a conjugated polymer emitter. Defects in opals give rise to allowed states inside the photonic stop band, which are probed by transmittance and reflectance spectroscopy. The emission spectrum of the polymer embedded in the defect layer is strongly modified and fingerprints of defect states located inside the stop band are recognized. Amplified spontaneous emission for these engineered photonic crystals is clearly observed.

We demonstrate control of the photoluminescence spectra and decay rates of water-soluble green-emitting conjugated polyrotaxanes by incorporating them in polystyrene opals with a stop-band spectrally tuned on the rotaxane emission (405–650 nm). We observe a suppression of the luminescence within the photonic stop-band and a corresponding enhancement of the high-energy edge (405–447 nm). Time-resolved measurements reveal a wavelength-dependent modification of the emission lifetime, which is shortened at the high-energy edge (by ∼11%, in the range 405–447 nm), but elongated within the stop-band (by ∼13%, in the range 448–482 nm). We assign both effects to the modification of the density of photonic states induced by the photonic crystal band structure. We propose the growth of fluorescent composite photonic crystals from blends of “solvent-compatible” non-covalently bonded nanosphere-polymer systems as a general method for achieving a uniform distribution of polymeric dopants in three-dimensional self-assembling photonic structures

We report on the preparation and optical characterization of three dimensional colloidal photonic crystal (PhC) containing an engineered planar defect embedding photoactive push-pull dyes. Free standing polystyrene films having thickness between 0.6 and 3 µm doped with different dipolar chromophores were prepared. These films were sandwiched between two artificial opals creating a PhC structure with planar defect. The system was characterized by reflectance at normal incidence angle (R), variable angle transmittance (T) and photoluminescence spectroscopy (PL) Evidence of defect states were observed in T and R spectra which allow the light to propagate for selected frequencies within the pseudogap (stop band).