EPR study of Ce3+ ions in lutetium silicate scintillators Lu2Si2O7 and Lu2SiO5

Two Ce3+-doped scintillator crystals, LSO (Lu2SiO5:Ce) and LPS (Lu2Si2O7:Ce), are studied by EPR spectroscopy. The analysis indicates that Ce3+ substitutes for Lu3+ ion in a C2-symmetry site for LPS and in two C1-symmetry sites for LSO, with a preference for the largest one, with 6+1 oxygen neighbors. Angular dependence of the EPR spectrum shows that the electronic ground state of Ce3+ is different in these two matrices. It is mainly composed of |MJ|=5/2 state in LPS and |MJ|=3/2 state in LSO. The temperature dependence of the linewidth shows a noticeably long spin lattice relaxation time, especially in LPS, which is the result of a stronger crystal field in LPS than in LSO.