Electron paramagnetic resonance study of the site preferences of Gd 3+ and Eu 2+ in polycrystalline silicate and aluminate minerals
Electron paramagnetic resonance (EPR) measurements were made on Gd 3+ and Eu 2+ ions in polycrystalline samples to determine the nature of the sites occupied by those ions in mineral structures. Both Gd 3+ and Eu 2+ ions were incorporated at Ca 2+ structural sites in β-Ca 2SiO 4, pseudo-CaSiO 3, CaMgSiO 4, CaMgSi 2O 6, hex-CaAl 2Si 2O 8, CaAl 2O 4, and Ca 3Al 2O 6. For tri-CaAl 2Si 2O 8, Eu 2+ was incorporated at a Ca 2+ site and Gd 3+ was incorporated at a site where the crystalline electric field was disordered. That difference in behavior may contribute to the anomalous behavior of Eu in plagioclase feldspar. Both Gd 3+ and Eu 2+ were incorporated as aggregates or clusters of those ions in Mg 2SiO 4 and clino-MgSiO 3.