A ZnO crystal, grown by the seeded chemical vapor transport method, was irradiated near room temperature with 1.5MeV electrons. The resulting O and Zn vacancies were characterized using optical absorption, photoluminescence , and electron paramagnetic resonance. A broad absorption band peaking near 409nm gives the irradiated crystal a yellow colour and was attributed to neutral O vacancies. A broad emission band peaking near 700nm in the irradiated crystal was attributed to donor–acceptor pair recombination involving Zn-vacancy acceptors. Electron paramagnetic resonance spectra from Fe3+ ions and singly ionized non-axial Zn vacancies were observed at 30K after the irradiation, but before illumination. Illumination with 325nm light at low temperature eliminated the Fe3+ signal while producing spectra from singly ionized O vacancies, neutral Zn vacancies, and singly ionized axial Zn vacancies. The light also produces electron paramagnetic resonance spectra from Zn vacancies with an OH- ion occupying an adjacent O site. No correlation was found between the green emission and the presence of O and/or Zn vacancies.

EPR and Optical Study of Oxygen and Zinc Vacancies in Electron-Irradiated ZnO. Kappers, L.A., Gilliam, O.R., Evans, S.M., Halliburton, L.E., Giles, N.C.: Nuclear Instruments and Methods in Physics Research B, 2008, 266[12-13], 2953-7