EPR of Nd3+ and Er3+ ions in aluminum borates YAl3(BO3)4 and EuAl3(BO3)4

► The absorption lines broadening is described by the Orbach-Aminov process. ► A decrease of g-factor of Er3+ ion in crystals is caused by spin-phonon interaction. ► The hyperfine interaction constants are determined. ► The relaxation velocity of Er3+ ions is lower than that of Nd3+ ions.