Spectroscopic studies of magnetic transitions in TbPO4

In TbPO4, an antiferromagnetic-phase transition is accompanied by a cooperative Jahn–Teller effect involving a Tb ion-lattice coupling that induces a tetragonal-to-monoclinic distortion of the crystal lattice and an associated readjustment of the Tb electronic states as required by the lowering of the rare-earth-site symmetry. The laser-excitation and emission spectra of TbPO4 and 0.1% Tb-doped YPO4 single crystals were studied at temperatures below and above the phase transitions. The line shapes of transitions in the stoichiometric compound are unusually broad and asymmetric while those observed for the dilute compound are relatively sharp. In addition, the TbPO4 spectra show an anomalous temperature dependence near the phase transition, indicating strong interactions of the rare-earth ions with their local environments. In the present work, a comparison of the optical results with the results of new neutron-scattering measurements is made.