THE ANNEALING OF RADIATION-DAMAGE IN DEBEERS COLORLESS CVD DIAMOND

Electron-irradiated samples of polycrystalline CVD diamond plates, 400 mum thick, have been isothermally annealed at 650 and 700-degrees-C, and the intensity of the GR1 band measured at regular intervals. The time constants of 27 h and 11 h respectively, derived from the annealing curves, lead to a vacancy migration energy of 1.4 +/- 0.4 eV. As the GR1 band declines, there is a corresponding growth in the intensity of the 1.681 eV absorption band, indicating that this optical centre is a vacancy trapped at an impurity, probably silicon. The vibronic absorption band of the 1.681 eV centre has been studied for the first time and the Huang-Rhys factor determined to be 0.24 +/- 0.02. The temperature dependence of the zero-phonon line is much faster than would be expected for such a low Huang-Rhys factor and evidence is presented for another temperature-activated process which affects the intensities of both the absorption and the luminescence bands. The 1.681 eV zero-phonon transition is shown to be a doublet, due to a splitting of 0.8 meV in the excited state.