ESR and photo-ESR measurements of the VO+ centre were performed to determine the charge states of the oxygen vacancies in ZnO raw material and Li-doped ZnO ceramics. The temperature dependence of the relative ESR intensity and the optical excitation of the ESR signal of the VO+ centre were investigated. The results show, that in both samples the oxygen vacancies exist in the VO2+ and VO+ state only. The ionization energy of the VO+ centre was determined by analysing the decay of the intensity of the VO+ signal after turning off the optical excitation.ESR and Photo-ESR Investigations of the VO+ Centre in ZnO Raw Material and Li-Doped ZnO Ceramic Powder. Pöppl, A., Völkel, G.: Physica Status Solidi A, 1990, 121[1], 195-204