Photoconductivity and Photoluminescence Kinetics Associated with the Luminescence Center in Rutile (TiO2)

Abstract

The photoconductivity and photoluminescence kinetics associated with the infrared (IR) broadband photoluminescence in rutile were studied. The effects of temperature and IR irradiation on the photoconductivity and photoluminescence, and the temperature dependence of luminescence lifetime, were measured. The results of these measurements lead to a model of the luminescence center whose main features are: (i) excitation by both direct and indirect charge-transfer mechanisms and (ii) emission due to a transition from an excited state of the center, which lies 0.18 ± 0.02 eV below the edge of the conduction band, to the ground state. Differences between the kinetic growth of the photoconductivity and the photoluminescence are found because the luminescence intensity depends mainly on the hole traffic through the center, while the photoconductivity depends primarily on the electron concentration in the conduction band. The following parameters associated with the luminescence center were determined: lifetime of the excited state of the luminescence center, 3.6 × ${10}^{-5\mathrm{}}$ sec; capture cross section of the excited state, 5 × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$; and an oscillator strength of the luminescent transition of ${10}^{-4\mathrm{}}$.