The production rate and saturation point of Ti3+ defect sites on titanium dioxide P-25 and anatase nanoparticles doped with Au101(PPh3)21Cl5 (Au101) metal nanoclusters were investigated under synchrotron X-ray irradiation alone, as well as combined X-ray and UV radiation. The saturation point in the growth of the normalized relative populations of Ti3+ centers on anatase and P-25 titania nanoparticles with and without Au101 nanoclusters present at the surface was found to vary with the type of support. It was influenced by the presence of gold nanoclusters: a higher concentration of Ti3+ centers was generated where gold nanoclusters were deposited onto anatase nanoparticles and irradiated by both X-ray and UV photons, compared with X-ray irradiation alone. Conversely, all samples based on the TiO2 P-25 support displayed reduced levels of Ti3+ center populations at the saturation points under combined X-ray and UV combined radiation, compared to the samples exposed exclusively to X-ray radiation. The initial rate of production of Ti3+ defect sites was found to decrease for combined UV and X-ray irradiation in the case when Au101 was deposited onto anatase. However, the opposite trend in the initial production rate of Ti3+ centers was observed in the case of Au101 deposited onto the TiO2 P-25 surface.