Composite photonic crystals from semiconductor nanocrystal/polyelectrolyte-coated colloidal spheres

Submicrometer-sized polystyrene colloidal spheres were coated with hybrid films consisting of HgTe semiconductor nanocrystal (HgTe NC) and polyelectrolyte (PE) multilayers by the layer-by-layer (LbL) technique. The prepared coated spheres were crystallized, forming composite colloidal crystals. Increasing the number of the HgTe NC layers deposited on the colloidal spheres leads to an increase in both the diameter and the effective refractive index of the spheres, which causes a systematic red shift of the stop bands of the composite colloidal crystals. The photoluminescence properties of the HgTe NCs assembled around the spheres in the composite colloidal crystals are impacted by the stop band of the colloidal crystals, giving rise to modifications of their emission properties. A titanium(IV) isopropoxide (TIP)/isopropyl alcohol solution was infiltrated into the voids of the colloidal crystals, and after solidification of TIP and removal of the colloidal crystal template by calcination, composite TiO2/HgTe inverse opals with HgTe embedded in the interior surface of the macroporous TiO2 were obtained. The strategy presented demonstrates the feasibility of fabricating composite photonic crystals (both colloidal crystals and inverse opals) from nanoscale-coated colloidal spheres. Such composite opaline photonic crystals provide a means of combining electronic confinement, originating from the NCs, with photon confinement, due to the ordered dielectric structures, hence opening new avenues in the design and construction of novel electrooptical devices based on photonic crystals.