Electron Paramagnetic Resonance and Optical Absorption of Yellow Anatase TiO2 Single Crystal

Electron paramagnetic resonance (EPR) measurements revealed the inclusion of nitrogen in yellow anatase single crystals grown by chemical vapor transport using NH 4 Cl as the transport agent. The angular-dependence of EPR triplets suggests that nitrogen occupies a substitutional site of oxygen in the bulk. The paramagnetic nitrogen observed at room temperature becomes diamagnetic at lower temperatures by trapping another electron. Below 50 K, only one symmetric differential EPR signal from titanium with an unpaired electron can be observed. These changes in the electric states of nitrogen and titanium can be explained by the presence of oxygen vacancies and by the contribution of trapped electrons to oxygen vacancies. The optical absorption observed at 3.0 eV in an E ∥ a configuration, which is characteristic of yellow anatase is almost independent of temperature.