Temperature dependence of Eu-related EPR spectra in CsBr:Eu needle image plates

Vacuum-deposited CsBr needle plates doped with Eu2+ have been investigated with Q (∼34 GHz) and W (∼95 GHz) band electron paramagnetic resonance in a large temperature interval (4 K: room temperature). At low temperatures (<35 K), two Eu-related centers were found with different symmetry (tetragonal and orthorhombic), while in earlier studies at room temperature only one center was found with tetragonal symmetry. Possible models for the three defects are investigated, taking into account their temperature behavior, their symmetry, and the atypical values of their zero-field splitting parameters.