ELECTRON-PARAMAGNETIC-RESONANCE STUDY OF AN AL-ASSOCIATED OXYGEN HOLECENTER IN KTIOPO4-AL CRYSTALS

Electron paramagnetic resonance (EPR) has been used to study an oxygen hole centre (O-) produced in Al-doped KTiOPO4 crystals gamma-irradiat ed at 300 K. The EPR spectrum exhibited by this point defect can be ob served at temperatures between 300 and 100 K. A six-line hyperfine spl itting which is ascribed to one Al-27 nucleus and a doublet splitting which is ascribed to one P-31 nucleus have been observed at 150 K. At 150 K, the principal g values are 2.0027, 2.0157 and 2.0464, the princ ipal values of the Al-27 hyperfine splitting are 6.3, 7.4 and 7.5 G an d the principal values of the P-31 hyperfine splitting are 0.6, 2.5 an d 2.6 G. The hole is trapped at one of the titanyl oxygens and locally associated with an Al3+ impurity located at or near a Ti4+ site. The Al impurity stabilizes the oxygen hole center, which would not be stab le at room temperature in undoped crystals.