IDENTIFICATION BY ESR OF PB+-TYPE CENTERS IN LEAD-DOPED SRCL2

Several Pb+-type centres are produced in SrCl2:PbCl2 crystals by x-ray irradiation at 80 K and subsequent thermal and optical treatments. From the analysis of the electron-spin-resonance (ESR) and production properties, the dominant spectrum, with trigonal symmetry around [111], is attributed to a Pb+ ion located on a cation site with an anion vacancy in a nearest-neighbour position: the so-called Pb+(1) centre with the laser-active-type structure. Specific thermal treatments lead to two more Pb+ centres with the same symmetry. The analysis of their hyperfine interaction parameters shows that in both centres the Pb+ ion is subject to a strong odd crystal field too, but their defect structures could not be further elucidated. An additional spectrum with a small orthorhombic distorsion is observed in a more heavily doped crystal and is attributed to a lead dimer centre consisting of a Pb+(1) defect perturbed by a nearest-neighbour substitutional Pb2+ impurity.