Electron paramagnetic resonance and optical absorption studies of irradiated lithium aluminate

Using electron paramagnetic resonance (EPR) and optical absorption measurements, defect creation is studied in irradiated single crystals of lithium aluminate, γ-LiAlO2. The EPR observations show the presence of several paramagnetic defects in γ-LiAlO2 irradiated with 2.5 MeV electrons at 20 K and X-rays at room temperature. The major defect includes an electron trapped near an aluminium nucleus. Optical absorption measurements show four bands in the spectra of γ-LiAlO2 irradiated with 2.5 MeV electrons at 20 K and with 2 MeV He+ ions at room temperature and 77 K. By analogy with other oxides, the most intense band (at 5.25 eV) may be assigned to F+-centres. With that assumption, a configuration is proposed for the F+-centre consistent with the EPR observations. (author)