Paramagnetic ions in europium-doped distorted YAlO$_{3}$ perovskite

In yttrium orthoaluminate crystals doped with the 151Eu isotope, the paramagnetic centers Eu$^{2+}$, Cr$^{3+}$, Gd$^{3+}$, and Мо$^{3+}$ have been detected. The fine structure parameters of the spin Hamiltonian of these centers were determined or refined. The account of the orientational behavior of previously unobserved forbidden transitions has been taken for the Cr$^{3+}$ centers. It is shown that two Мо$^{3+}$ signals that are detected in magnetic fields parallel to the crystallographic axes do not belong to different molybdenum centers, but are two intra-doublet transitions of the same center.