Electronic structure of defects in oxides. Progress report, December 1, 1978-November 30, 1979

Excitation into the 6.1 eV F band in single crystal samples of α-Al2O3 produces a luminescence with a peak at 3.0 eV and a half-width of 0.36 eV at 4.40K. The temperature dependence of the half-width follows a hyperbolic cotangent relation with an effective frequency of 370 +- 20 cm-1. At 4.40K the fluorescence decay contains two components. One of these, which has a lifetime of 24 +- 2 ms, is assigned to a spin forbidden transition from the lowest lying component of the symmetry split 3p-like excited state of the F center to the 1A1 ground state. The other component has a lifetime of 272 + 10 ms at 4.40K and is assigned to phosphorescence due to shallow electron traps in the lattice. At 50.40K a single component is observed in the fluorescence decay, with a lifetime of 35 +- 2 ms. This fluorescence is assigned to a second spin forbidden transition of the F center. The excited states of the F+ center in neutron or proton irradiated SrO have been studied by measuring the temperature dependence of the yield and lifetime of the F+ fluorescence over the temperature range from 50K to 1400K. Both the fluorescence yield and lifetime decrease in two stages; one over the temperature range from 50K to 600K, and the other over the range 600K to 1400K. The results are interpreted in terms of a three level model of the F+ center which is suggested by recent theoretical work. The lowest radiative level, which has a lifetime of 0.42 μs, is found to be 0.05 eV below the conduction band. Another level is found only 0.005 eV above this radiative level. In order to account for the results, non-radiative decay to the ground state appears to occur from this second level