Photo-Stimulated EPR Spectroscopy of Oxygen Defects in a Rutile (TiO₂) Crystal Irradiated with Ar Ions

The electron paramagnetic resonance (EPR) spectra of oxygen-deficient rutile TiO_{2 – δ} under photoexcitation at low temperatures in the range of 15–40 K were measured. Excluding the early described Ti³⁺ centers, concentration of which is independent of photoexcitation, new EPR signals appear at various wavelengths (λ) of photoexcitation taken in the range 400–460 nm. From the analysis of the EPR data we conclude that the observed EPR signals can be attributed to either the positive-charged oxygen vacancies ( \({\text{V}}_{{\text{O}}}^{ + }\) ) with S = 1/2 (upon photoexcitation with λ ≤ 420 nm only), or more complex defects such as positively-charged [Ti³⁺–V_O]⁺ pairs with S = 1/2 and neutral complexes of (Ti³⁺–V_O–Ti³⁺) with S = 1. The latter is observed upon photoexcitation with a wavelength above 420 nm.