THE ROLE OF CERIUM SITES IN THE SCINTILLATION MECHANISM OF LSO

The crystal structure of Lu-2(SiO4)O:Ce (''LSO'') has two trivalent ca tion sites which may be occupied by Ce3+ to form luminescence centers. Previous investigations revealed the existence of two distinct sets o f Ce3+ excitation and emission spectra and suggested that the differen ces in the spectra are due to differences in the crystal fields at the two lattice sites that shift the 5d levels of Ce3+. In the present re port, we re-examine this issue and present new evidence which suggests a different interpretation. In particular, spectra measured at 13 K s uggest that both lattice sites may give rise to indistinguishable exci tation and emission spectra while the second set of observed spectra m ay arise from Ce3+ located in interstitial sites. The evidence for the interstitial sites is a disappearance of the doubler structure in the emission spectra and a large variation in the population of the sites as a function of total cerium concentration. In addition, the results indicate that the scintillation properties of LSO are influenced by t he relative population of Ce in interstitial sites compared to lattice sites as well as by differences in the transfer efficiencies to diffe rent sites.