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X-Ray irradiation at room temperature produces several paramagnetic centres in rare-earth activated K2YF5 crystals, whose thermal annealing behaviour can be linked with the occurrence of thermoluminescence (TL) glow peaks. In this paper, continuous wave (CW) and pulsed paramagnetic resonance techniques are used to study the structure of a very stable radiation-induced centre, which may be involved in the TL peak at ∼390 °C reported for Ce- and Tb-activated crystals. From the spectra the centre’s g tensor and hyperfine (nuclear quadrupole) tensors for several 19F and 39K neighbouring nuclei are extracted, but no self-hyperfine interaction could be detected. Based on the analysis of the interaction tensors, a model is constructed consisting of an oxygen-related radical (e.g. O− or O2−) on a substitutional F− position in the mirror plane of the YF7 polyhedra. Such a centre most probably corresponds to a trapped-hole state. [ABSTRACT FROM AUTHOR]

Fe3+ ions in hexagonal and cubic fluoroelpasolite crystals (AI2BIMIIIF6) have been investigated in a combined Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) study. A detailed analysis of the ENDOR spectra for the nearest 19F and 23Na shells in X (9.5 GHz) and Q band (34 GHz) allowed the complex EPR spectra to be disentangled and to determine the spin Hamiltonian parameters for the various S = 5/2 Fe3+ centres. W-band (95 GHz) EPR measurements as a function of temperature were performed to provide unambiguous evidence about the absolute signs of the Zero Field Splitting (ZFS) and SuperHyperFine (SHF) parameters for Fe3+ in Cs2NaAlF6 as already determined from the ENDOR work. It could be concluded that all principal 19F hyperfine values were positive, in agreement with earlier assignments in the literature for related systems. A comparative analysis of the 19F SHF data for Fe3+ at a perfectly octahedral site in the cubic crystal, and at two slightly trigonally distorted environments in the hexagonal crystals, indicates that the metal-to-ligand distance changes upon doping. The obtained set of parameters concerning one defect in various analogous environments can furthermore be used to test different methods of theoretical calculations for ZFS and SHF values. [ABSTRACT FROM AUTHOR]