Models of tetrahedral rare-earth clusters in cadmium fluoride crystals and paramagnetic resonance

The parameters of the zero-field level splitting of Gd3+ ions localized in three kinds of tetrahedral clusters are estimated within the superposition approximation. The structure of a cluster is determined by minimizing the energy of the crystal with the embedded cluster. As a result, the strong monoclinic EPR spectrum with b20 = −345 MHz is attributed to the [CdY2CdF26] cluster and a weaker spectrum with b20 ≈ −600 MHz is attributed to [Cd2YGdF26]. The difference between the absolute values of the calculated and experimental parameters b20 is explained by the fact that the experimental spectrum is due to gadolinium ions located in clusters that are part of associations.