Comparison of EPR spectra of the Gd 3+ ion‐doped YA l 3 ( BO 3 ) 4 , Eu A l 3 ( BO 3 ) 4 , and Tm A l 3 ( BO 3 ) 4 single crystals

The EPR spectra of Gd 3+ ion replacing Y 3+ or rare‐earth (RE) ions in aluminum borates REAl 3 (BO 3 ) 4 (RE = Y 3+ , Eu 3+ , Tm 3+ ) have been studied. The spin‐Hamiltonian parameters of an impurity Gd 3+ ion in these crystals were determined. The basic atom coordinates in the structure of TmAl 3 (BO 3 ) 4 crystal have been established. Distortions of the Gd 3+ ion nearest environment were analyzed within the framework of the superposition model of zero‐field splitting. Theb 2 0parameter change in isomorphic aluminum borates is shown to be determined by change of the angle between the Gd 3+ O 2− bond and the C 3 ‐axis.