Calculation of photonic energy bands of TiO2 hollow spherical arrays. 
The photonic energy bands of titanium dioxide (TiO2) hollow spherical arrays, which are self-assembled photonic crystals, were investigated.  The finite-difference time domain (FDTD) method was applied to both the face-centred-cubic (fcc) and body-centred-cubic (bcc) packing structures of TiO2 hollow spherical arrays to determine the energy bands from the perspective of photoelectrode applications.  Calculations were carried out on the basis of the TiO2 shell wall thickness.  The spectral behaviour of light in the hollow spherical arrays was also studied, with particular interest devoted to the pseudogap found in one of the structures.  A three-dimensional (3D) TiO2 hollow spherical array was then experimentally synthesized in three steps: the preparation of synthetic opal templates, replication by spin coating, and sintering.  The diffuse scattering spectrum of the obtained array was finally measured and compared with the calculated photonic band structure.