Nd3+ ions at the low-symmetry sites of β-BaB2O4 single crystals studied by electron paramagnetic resonance spectroscopy -: art. no. 184107

An electron paramagnetic resonance (EPR) study of Nd3+ ions in single crystals of the low-temperature phase of barium metaborate (beta-BaB2O4 or BBO) is presented. The EPR spectrum shows the existence of various slightly different Nd3+ centers. The g matrices of the three more abundant centers have been determined through the analysis of the angular dependencies of the spectrum in two planes of the crystal. The principal g-axis systems do not allow a straightforward assignment of the centers to a specific lattice cation site because of the low site symmetry (C-1 in all cases). To overcome this problem we have developed a method to calculate principal g-axis systems by constructing and diagonalizing the crystal-field energy matrix for the ground I-4(9/2) level of Nd3+, including the Zeeman interaction. The superposition model of the crystal field has been employed to estimate the crystal-field B-n(m) parameters for this ion in BBO, as they are unknown. From this study it is concluded that neodymium is incorporated in the low-symmetry Ba2+ site. Possible reasons for the appearance of different Nd3+ centers are discussed.