Jahn-Teller effect and features of divalent copper ion behavior in multicomponent borate crystals.

Crystals of YGa3(BO3)4, YAl3(BO3)4, EuGa3(BO3)4 and EuAl3(BO3)4 with copper alloy were studied by electron paramagnetic resonance and X-ray diffraction analysis. The lattice parameters and coordinates of copper-doped boron atoms were determined. The study of EPR spectra showed that copper is in the divalent state and replaces aluminum ions with C2 node symmetry. In YAl3(BO3)4:Cu crystals, a ligand structure exists due to the interaction of copper electrons with yttrium nuclei. The parameters of the spin Hamiltonian describing the behavior of the Cu2+ spectrum have been determined. The deviation of the Z-axis spectra from the C3 axis by 54(1)° is due to Jahn-Teller vibronic interaction and monoclinic distortion. In the EuGa3(BO3)4 crystal, a new spectrum 2 was found, which also belongs to divalent copper but is observed at an excited state 31 cm-1 away from the ground state. Above 70 K, an isotropic EPR line with a width of 450 Gs, g = 2.1, appears and exists up to room temperature.