Photoluminescence and Optically Stimulated Luminescence Studies of LiAlO2 and LiGaO2 Crystals

Copper diffusion in LiAlO2 creates large photoluminescence (PL) and optically stimulated luminescence (OSL) signals that are not present in as-grown samples. The main PL band peaks at 3.45 eV (359 nm) and is excited by a band peaking at 4.54 eV (273 nm). After x-ray irradiation, OSL results from 425-500 nm continuous wave light. An optical absorption band in the same region decays during optical stimulation. Analysis of the wavelength dependence of the OSL emitted light reveals a band that is similar in peak location and width to the PL band suggesting that they occur at the same copper defect. The defects causing this optical behavior were identified using electron paramagnetic resonance (EPR) spectroscopy. During x-ray irradiation, Cu+ ions trap holes to become Cu2+ ions while Fe2+ ions trap electrons to become Fe+ ions. As a result of optical stimulation, released electrons recombine with holes at the Cu2+ ion sites. Copper diffusion in LiGaO2 creates a large PL signal peaking at 2.33 eV (532 nm) that is excited by 3.50 eV (354 nm) light. This PL signal in LiGaO2 is assigned to Cu+ ions substituting for Li+ ions