The room temperature Gd3plus;EPR spectrum in SrF2containing Ce3plus;as a second dopant exhibits three types of symmetry sites: cubic, trigonal, and tetragonal. Relative intensities of the spectra from these sites have been determined as a function of the Ce3plus;codopant level in crystals having nominally 0.1 molar percnt; of Gd3plus;. At low Ce3plus;concentrationslpar; 0.1thinsp;molarthinsp;percnt;rpar;, the tetragonalhyphen;tohyphen;trigonal intensity ratio is1.85 plusmn; 0.25, with the cubic site intensity accounting for less than one tenth of the total observed intensity. At higher Ce3plus;concentrations (up to 0.8 molar percnt;), the cubic site intensity grows and the intensity of both axial sites decreases. This increase of cubic intensity is at variance with the generally accepted model of nonlocalized cubic compensation of the Gd3plus;, and a phenomenological explanation based on a local cubic phase in which rare earth ions are essentially surrounded with interstitial compensating fluorines is presented.
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