Electron paramagnetic resonance of rutile pigments

An Electron Paramagnetic Resonance study of rutile (TiO(_2)) pigments doped with either iron or chromium has been performed. The spectra of the Cr(^3+) ion has been observed and confirmed by computation. In iron doped pigments a signal with g = 4.28 was observed and has been attributed to the Fe(^3+) ion in a site of rhombic symmetry. The effect of irradiation by light on the Fe(^3*) ion in a substitutional site has been examined and seen to be different from that for single crystal samples ; only wavelengths longer than 700 nm affect it. A light-generated line was observed with 'g' values g(_11) = 2.010, g(_1) = 2.005. The response of this line is related to the concentration of iron. The data has been analysed and correlates reasonably well with accepted models for the positions of the defect centres within the band gap.