Self-assembled zno colloidal photonic crystals: Light channels in cracks

Large-area films of colloidal photonic crystals (PCs) were prepared by self-assembly technique. The films contain ordered PC domains separated by cracks. The size of the domains and cracks can be controlled by the drying process. The angular dependence of the stop-band was studied by changing the angle of incidence θ between the beam and the (1 1 1) direction, from 0° to 60°. The observed stop-bands are almost independent of the density of cracks. It is seen that as the angle increases the stop-band shifts to shorter wavelengths. We demonstrate that the photoluminescence emission spectra depend on the PC domain size and on the concentration of cracks. For a film with small density of cracks, we observed light channeling through cracks probably due to light inhibition.