"Photocatalysts that have high activity using wavelengths of light in the visible spectrum (380 nm < λ < 500 nm) ...has been achieved by altering the ... Doping of TiO2 with s (for example, V, Cr, Mn, Fe and Ni) as well as with Ag, Au and Ru, have been demonstrated to red-shift the TiO2 absorption band from the UV into the visible region..."