Electron-irradiated type-IIa diamonds were investigated by using positron lifetime and Doppler broadening spectroscopy during illumination with photon energies ranging from 2.2 to 3.5eV. The illumination caused neutral vacancies to become negatively charged, and the charging was most effective at photon energies close to 2.85eV. This suggested that the electronic level for the negatively charged monovacancy was situated 2.85eV above the valence band. The photon-flux dependence of charging at a photon energy of

2.83eV depended strongly upon temperature, and was attributed to recombination between holes and negatively charged monovacancies.

Positron Annihilation Study of Vacancies in Type-IIa Diamonds Illuminated with Monochromatic Light. S.Dannefaer, A.Pu, D.Kerr: Diamond and Related Materials, 2001, 10[12], 2113-