Oxygen vacancy centres induced by electron irradiation in LiNbO3

Abstract Optical absorption has been used to monitor the damage induced in LiNbO3 by irradiation with electrons having energies up to 2.0 MeV. A well defined threshold has been found corresponding to oxygen displacements and a binding energy of 53 eV, in accordance with data for other oxides. The absorption spectra for the crystals irradiated above threshold are similar to those observed for thermally reduced samples. It is concluded that oxygen-vacancy (F-type) centres are formed under both treatments. On heating samples after irradiation, a transfer process is induced from the 390 nm (3.2 eV) and 480 nm (2.6 eV) bands to the 750 nm (1.6) band, previously associated to small polarons (Nb+4). The effects is completely reversible on cooling, suggesting a clear interrelation among the involved centres.