Resolve electric dipole moments for distorted Tm3+ sites #2 and #3 in TmAl3(BO3)4

Determine the effective electric dipole moments (matrix elements) of the crystal-field A1 → E transitions for Tm3+ ions occupying the distorted D3-symmetry sites #2 and #3 in TmAl3(BO3)4, which were not resolved from terahertz transmission and polarization-rotation spectra due to the small concentrations of these sites and the weak intensities of their resonance modes.

Background

The study analyzes terahertz transmission and polarization-rotation spectra in TmAl3(BO3)4, attributing the observed crystal-field A1 → E transitions and their fine structure to three types of Tm3+ sites arising from local distortions, primarily associated with Bi3+ impurities. A cluster model with site types #1 (weakly distorted), #2 (next-nearest neighbors to Bi3+), and #3 (nearest neighbors to Bi3+) is used to fit both transmission and optical-activity data.

From these fits the authors extract effective magnetic and electric dipole moments for the transitions. While electric dipole moments for site #1 could be quantified, the moments for sites #2 and #3 were not resolved due to the small fractions of these sites and their weak resonance intensities, leaving these specific matrix elements undetermined.

References

Electric dipole moments for the sites #2 and #3 could not be resolved due to small concentrations of these sites and due to weak intensities of the resonance modes.

— Terahertz optical activity near crystal field transitions of Tm3+ ions in magnetoelectric alumoborates  (2604.02193 - Kuzmenko et al., 2 Apr 2026) in Section III (Results and discussion), paragraph preceding Table 1