The electronic structure of bivalent Cu off-center complexes was estimated from electron paramagnetic resonance and electron–nuclear double resonance spectroscopic data. The electronic structure parameters which characterized the unpaired-electron density in the vicinity of the nucleus of a Cu impurity ion were determined. The parameters of the covalent bonds between an impurity Cu ion, and the 3 groups of F-ions nearest to the impurity, were calculated. It was shown that states of the ground electron configuration of the bivalent Cu impurity complex involved a mixture of excited electron configurations due to electron transfer from the ligand to 4s and 4p unfilled shells of the Cu ion.

Electronic Structure of Bivalent Copper Off-Center Complexes in SrF2 Crystals from Data on EPR and ENDOR Spectroscopy. V.A.Ulanov, O.A.Anikeenok, M.M.Zaripov, I.I.Fazlizhanov: Physics of the Solid State, 2003, 45[10], 1906-9