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 YAl antisite ions. After trapping an electron they become paramagnetic YAl2+ 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 YAl 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 89Y nuclear magnetic resonance.