Abstract
A detailed ESR analysis of Eu2+ centres in CaSO4, produced by X-irradiation of CaSO4:Eu3+ single crystals, has been carried out at 295K using microwave frequencies of 36.5 and 9.2 GHz. The spectra can be described by an orthorhombic spin Hamiltonian and show effects due to large magnetic hyperfine, nuclear quadrupole and nuclear Zeeman interactions it is shown that the bonding at the Eu2+ site has a significant covalent contribution. The observed Eu2+ centres are produced by the reduction of those Eu3+ ions that replace Ca2+ substitutionally and that are not locally charge-compensated.

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