Electron paramagnetic resonance study of an Al-associated oxygen hole center in kTiOPO4:Al crystals

Electron paramagnetic resonance (EPR) has been used to study an oxygen hole centre (O−) produced in Al-doped KTiOPO4 crystals γ-irradiated at 300 K. The EPR spectrum exhibited by this point defect can be observed at temperatures between 300 and 100 K. A six-line hyperfine splitting which is ascribed to one 27Al nucleus and a doublet splitting which is ascribed to one 31P nucleus have been observed at 150 K. At 150 K, the principal g values are 2.0027, 2.0157 and 2.0464, the principal values of the 27Al hyperfine splitting are 6.3, 7.4 and 7.5 G and the principal values of the 31P hyperfine splitting are 0.6, 2.5 and 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 stable at room temperature in undoped crystals.