EPR of cubic Pr3+in fluorite

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Abstract
EPR of the cubic Pr3+ in fluorite, the only 4fn ion with a triplet Gamma 5 ground state in this lattice, is reported. Three cubic EPR spectra corresponding to the normal Delta M=1 transitions, the double-quantum Delta M=2 transitions and the half-field single-quantum Delta M=2 transitions are observed, all of them showing hyperfine structure due to the 141Pr nucleus. The spin-Hamiltonian parameters determined from the double-quantum spectrum are g=1.936+or-0.005 and A=(836+or-3)*10-4 cm-1. The possible causes for lowering the g-value from the value of two expected for a pure 3H4 Gamma 5 triplet are reviewed. An additional tetragonal centre (g/sub ///=1.930+or-0.008; A=(926+or-2)*10-4 cm-1, gperpendicular to <0.1, S=1) first reported by Wetsel et al. (1969) from APR measurements is also observed and a tentative model for this centre is discussed.