Is it effective to harvest visible light by decreasing the band gap of photocatalytic materials?

In situ variations in the electron work function and photo-current of TiO2 nanotubes demonstrate that long-wavelength illumination only has a minor effect on the excitation of electrons in the nanotubes after being exposed to short-wavelength light or when the short-wavelength light coexisted, indicating that the solar spectrum may not be utilized as efficiently as expected by extending the absorption spectrum of the photocatalytic material to visible light range with decreased band gaps. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3690052]