Study of the Kramers rare earth ions ground multiplet with a large orbital contribution by multifrequency EPR spectroscopy: Ce3+ in PbWO4 scintillator

A multifrequency Electron Paramagnetic Resonance (EPR) investigation of Ce3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (CMF) (X-band: 9.43 GHz) and at the high frequencies/fields (HF) 95, 190 and 285 GHz was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective spin one-half system in a tetragonal site symmetry. The diagonal values of the effective g matrix of the lowest doublet of the ground multiplet, g‖ and g⊥, are frequency dependent at high fields. For the magnetic field perpendicular to the tetragonal axis, the g⊥-parameter exhibits also a small azimuthal angular dependence, which is frequency dependent, corresponding to the tetragonal S4 symmetry. These HF effects are associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. The CMF and multifrequency HF-EPR analysis gives a good description of the magnetic properties and allows an estimation of the crystal field splitting of the ground multiplet of Ce3+ ions with tetragonal symmetry S4 in the PbWO4 scintillator.