Tetragonally distorted Cr2+ ions in BaF2 and SrCl2 studied by ESEEM spectroscopy

Electron spin echoes on tetragonally distorted non-Kramers Cr2+ ions in chr omium doped BaF2 and SrCl2 single crystals have been observed. The superhyp erfine interaction (shf) with the nearest halide ions has been studied usin g the electron spin echo envelope modulation (ESEEM) signal. For Cr2+ in Ba F2 the nearest coordination shell consists of four equivalent fluorine ions in a plane perpendicular to the defect tetragonal axis, the Cr2+ ion being off-centre displaced towards the fluorine plane. The Cr2+ Shf tensor for B aF2 has been determined. For SrCl2:Cr ESEEM signals associated to the shf i nteraction with nearest chloride ions were observed but the measurements di d not allow us to give a definitive defect model in this case.