Single-crystal EPR of the Eu2+ ion in pentacalcium-oxide trialuminate, 5CaO·3Al2O3 Original Research Article

X-band (∼9.8 GHz) EPR studies on a single crystal of pentacalcium-oxide trialuminate (5CaO·3Al2O3) doped with Eu2+ were carried out at 4.2, 77.4 K and in the range 120–300 K. The site symmetry, as revealed by the angular variation of the EPR spectrum, was found to be nearly axial. The Eu2+ spin-Hamiltonian parameters were estimated from the positions of the EPR lines at various temperatures. The absolute sign of the zero-field splitting parameter, B20, was determined to be positive from the relative intensities of lines at liquid-helium temperature. The resolved Eu2+ hyperfine (HF) structure was observed only for a few fine-structure EPR lines, and only at some orientations of the external magnetic field. HF-interaction constants for the 151Eu and 153Eu isotopes were estimated from an analysis of the partly resolved HF structure.