EPR study of the low-spin state of Ru3+in the YAl3(BO3)4 and EuAl3(BO3)4 aluminum borates

New data on the ground state of impurity Ru3+ ions in the crystals of YAl3(BO3)4 and EuAl3(BO3)4 aluminum borates were obtained. It was shown that Ru3+ ion replaces trivalent rare-earth ions without breaking the symmetry of the site. The crystal field acting on 4d5 ions forms an EPR spectrum, which is described by the spin Hamiltonian with S=1/2. The spin-Hamiltonian parameters determined are equal to gII=1.963, g⊥=3.796, AII=43.03*10−4 cm−1, A⊥=84.86*10−4 cm−1 in the YAl3(BO3)4 crystal (at Т=15 K) and gII=2.016, g⊥=3.796 in the EuAl3(BO3)4 crystal (at Т=15 K). It is found that the value of ∆g=gII-g⊥ is an indicator of distortions of nearest environment of Ru3+ ion. The angle between the C3 axis and the direction into nearest oxygen ion was determined. The EPR linewidth of Ru3+ ion increases with increasing temperature due to the dipole-dipole and exchange interactions with the excited states of the host lattice Ru3+ ion.