EPR investigations on europium(II)-doped aluminates

The europium(II)-doped aluminates, SrAl2O4 and CaAl2O4 with beta-tridymite structure and BaMgAl10O17 with beta-Al2O4 structure, have been investigated by means of EPR spectroscopy. From the complicated X-band EPR spectra observed for SrAl2O4 : Eu,Dy and CaAl2O4 : Eu,Nd it is deduced that they have large zero-field splittings in contrast to BaMgAl10O17 : Eu. High frequency EPR spectroscopy at 180 GHz shows symmetrical weak satellites on both sides of the strongest resonance centred around at 6.45 T. Spectral simulation with second order perturbation has made it clear that for SrAl2O4 : Eu,Dy the europium(II) ions occupy three different sites, while for the CaAl2O4 they occupy a single site with trigonal anti-prism symmetry, despite the fact that there are two other sites associated with octahedral symmetry.