Optically detected magnetic resonance investigation of oxygen luminescence centres in BaF₂

The structure of two oxygen-related luminescence centres in oxygen-doped BaF₂ was investigated by means of photoluminescence (PL) and photoluminescence-detected electron paramagnetic resonance (PL-EPR). One of the oxygen-related luminescences peaking at 2.83 eV is associated with an excited triplet state (S = 1) of an oxygen-vacancy complex with the z-axis of the fine-structure tensor parallel to the 〈110〉 direction. This complex can be described as an oxygen on a fluorine lattice site with a next-nearest fluorine vacancy along the 〈110〉 direction. The luminescence at 2.25 eV is also associated with a triplet state. Its PL-EPR spectrum is probably due to oxygen-vacancy complexes with a nearest fluorine vacancy along the 〈100〉 direction.