Hole and electron traps in the YAlO3 single crystal scintillator

The processes of hole and electron localization in YAlO3 single crystals were investigated by electron-spin resonance. It was found that holes created by UV or x-ray irradiation are trapped at regular oxygen ions forming two types of O- hole centers corresponding to hole localization at two inequivalent oxygen ions which are located in Y and Al planes, respectively. The hole can be either autolocalized or additionally stabilized by a defect in the neighborhood of the oxygen ion such as yttrium vacancy or an impurity ion at Y site. This leads to a variety of O- centers which differ both by thermal stability (from about 14 K up to room temperature) and spectral parameters. Electron-type trapping sites are assigned to Y-Al antisite ions. After trapping an electron they become paramagnetic Y-Al(2+) centers. They are found in several configurations with thermal stability up to above 300 K that enables the radiative recombination of freed holes with such localized electrons and the appearance of thermoluminescence peaks. It is shown that the electron trapped around Y-Al antisite ion is additionally stabilized either by an oxygen vacancy or by a defect at Y site. The yttrium antisite ions in the lattice were directly identified by Y-89 nuclear magnetic resonance.