Light-induced absorption of Ru-doped Bi12TiO20 crystals

Abstract

The effect of ruthenium doping on optical properties of Bi12TiO20 (BTO) single crystals is studied. A low concentration of ruthenium do not change absorption behavior of BTO, however higher ruthenium addition significantly shifts the optical absorption to the near infrared spectral region with an absorption shoulder appearing around 1.8 eV. The absorption coefficient increases with increasing the Ru concentration. Light-induced absorption changes are observed and the dynamics of build-up and dark decay processes are investigated. Results show that concentration of shallow levels increase with Ru content. Evolution of the build -up and dark decay of light induced absorption consists of fast and slow components: the first process occurs within few seconds, while the second one needs several hours (or days). It is established that light-induced absorption can be modified by preliminary illumination and thermal treatments thus multilevel lead to the transient and persistent parts of light-induced absorption. A model, assuming one deep and two shallow levels is proposed to explain the bi-exponential behavior of the build-up and the dark decay of light- induced absorption when the crystals are preliminary annealed in oxygen atmosphere.