کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5399331 | 1505896 | 2015 | 7 صفحه PDF | دانلود رایگان |
- Copper is diffused into LiAlO2 crystals at high temperature.
- Cu+ ions at Li+ sites cause PL at 359Â nm and PLE at 273Â nm.
- x-Rays convert Cu+ to Cu2+ by trapping holes and Fe2+ to Fe+ by trapping electrons.
- OSL emission occurs at 357Â nm with stimulation light in the 425-500Â nm region.
- The basic OSL mechanism is established by combining OSL, PL, PLE, and EPR.
A large optically stimulated luminescence (CW-OSL) response has been observed from bulk lithium aluminate (LiAlO2) crystals that have been copper-diffused. After introducing the copper, an optical absorption band peaking at 277Â nm is present and is assigned to Cu+ (3d10) ions at Li+ sites. Photoluminescence (PL and PLE) from copper-diffused samples shows an emission band near 359Â nm and an excitation band near 273Â nm. These PL bands are also assigned to the Cu+ ions. After an irradiation at room temperature with x-rays, the copper-diffused crystals give an intense OSL signal when stimulated with light in the 425-500Â nm region. The OSL emitted light has a peak near 357Â nm and thus is directly associated with recombination at a Cu ion. Electron paramagnetic resonance (EPR) shows that the x-rays produce two distinct Cu2+ (3d9) centers, both at Li+ sites. One of the trapped-hole centers is a Cu2+ with no nearby defects and the other is a Cu2+ with a neighboring Li+ vacancy. Monitoring the EPR spectra before and after OSL shows that only the isolated Cu2+ ions (i.e., those with no nearby defect) participate in the OSL process. The electron traps participating in the OSL are shown with EPR to be transition-metal ions that are unintentionally present. Specifically, Fe2+ ions replacing Li+ ions, possibly with a nearby lithium vacancy, convert to Fe+ (3d7) ions when they trap an electron during irradiation. These electrons are optically released by the OSL exciting light and migrate to the holes trapped as isolated Cu2+ ions, where electron-hole recombination gives the characteristic Cu+ emission. By combining OSL, PL, and EPR, we establish the general OSL mechanism in copper-diffused LiAlO2 crystals.
Journal: Journal of Luminescence - Volume 164, August 2015, Pages 105-111