Fig. 1(a) shows the UV–Vis absorption spectra of pure TiO2, Ag doped TiO2 & Zr and Ag co-doped TiO2. A definite band edge in the UV region at 300–350 nm seen in the spectra which could be assigned to photo excitation from valence band to conduction band.
It is interesting to note that the sample doped with silver (Ag doped TiO2) has shown lower shift compared to Zr and Ag codoped TiO2 (0.8 mol%), which has shown a significant red shift to higher wave length. This shift was observed to increase with increasing levels of Zr and Ag, indicating enhancement in the optical activity of the samples. The energy gap (Eg) was calculated from the equation