Photoactive spherical colloids for opal photonic crystals

The synthesis and characterization of submicrometersized polymer particles, functionalized by different techniques with fluorescent dyes and featuring tunable surface charges, are described. Dyes with a polymerizable moiety were incorporated during emulsifier-free or seeded emulsion polymerization, whereas nonpolymerizable dyes were included into preformed nanoparticles by a swelling and deswelling process. The particle surface charge was controlled through the choice of suitable initiators. All the nanoparticles were successfully used to grow high optical quality opal photonic crystals by the vertical deposition technique. Optical characterization of such photonic crystals pointed out the presence of the optical stop band and the high-energy van Hove-like structures, both scaling with the particle diameter according to the scaling laws of photonic crystals and possessing the expected angular dispersion. These results are indicative of the high size uniformity and of the surface quality of the nanospheres independently on the synthetic method adopted. Preliminary data seem to suggest some effect of the opal photonic band structure on the dye fluorescence spectra.