Single-crystal EPR of the Eu2+ ion in pentacalcium-oxide trialuminate, 5CaO center dot 3Al(2)O(3)

X-band (similar to9.8 GHz) EPR studies on a single crystal of pentacalcium- oxide trialuminate (5CaO . 3Al(2)O(3)) 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 t he 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 spli tting parameter, B-2(0), was determined to be positive from the relative in tensities of lines at liquid-helium temperature. The resolved Eu2+ hyperfin e (HF) structure was observed only for a few fine-structure EPR lines, and only at some orientations of the external magnetic field. HF-interaction co nstants for the Eu-151 and Eu-153 isotopes were estimated from an analysis of the partly resolved HF structure. (C) 2000 Elsevier Science Ltd. All rig hts reserved.