Photoactive systems based on semiconducting metal oxides

Engineering defects in semiconducting metal oxides is a challenge that remains at the forefront of materials chemistry research. The formation of novel states inside the band gap, allowing charge separation with energy lower than the pristine material band gap is one of the aim of the solid state research in the last few years. The use of dopants as well as the formation of heterojunctions between the interfaces that are formed by the mixing of different oxides are different strategies to tune the photochemical and photocatalytic properties of semiconducting oxides, boosting visible-light harvesting and charge separation events. These are key elements in promoting solar driven chemical reactions. The contribution of electron magnetic resonance techniques, and in particular of CW-EPR, to the experimental research on photocatalytic phenomena is described in this chapter. The role of the EPR technique in unravelling the nature and the features of extrinsic point defects in semiconducting oxides is evidenced using the important example of the photoactive doped center and the formation of heterojunction in various semiconducting oxides. Moreover, EPR can be used to monitor the processes that follow the initial photoinduced charge separation in photocatalysis, namely the stabilization, migration and surface reactivity of electrons and holes.