Study of the Kramers rare earth ions ground multiplet with a large orbital contribution by multifrequency EPR spectroscopy: Ce~(3+) in PbWO_4 scintillator

摘要

A multifrequency Electron Paramagnetic Resonance (EPR) investigation of Ce' impurities in PbWO_4 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 S_4 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 Ce~3 ions with tetragonal symmetry S_4 in the PbWO_4 scintillator.