Thermoluminescence and scintillation properties of rare earth oxyorthosilicate scintillators

In recent years, the scintillation properties of several cerium-doped rare earth oxyorthosilicate scintillators, [Ln.sub.2]Si[O.sub.5]:Ce where Ln = Y, La-Lu, have been reported and, in some cases, extensively studied [1]-[3]. In addition, binary and ternary compounds such as [(Lu,Y).sub.2]Si[O.sub.5]:Ce, [(Lu,Gd).sub.2]Si[O.sub.5] and [(Lu,Y,Gd).sub.2]Si[O.sub.5]:Ce have been reported [3]-[7]. All of these crystals have either monoclinic P or C structures with characteristic Si[O.sub.4] tetrahedra and trivalent cations occupying two unique crystallographic positions [8], [9]. The trivalent cerium activator ions are assumed to occupy the cation lattice sites and possibly interstitial positions as well. The excited 5d state of [Ce.sup.3+] is split into three observable levels with luminescence emission occurring only from the lowest 5d level to the 4f ground state (~3 eV) with a Stokes shift of ~0.5 eV. The bandgap is about 6 eV, and the index of refraction is close to 1.8, with some variation according to crystallographic direction. Despite these similarities, in somecases, differences in scintillation efficiency, decay time, rise time, and phosphorescence time profiles have been observed. In this paper, we combine thermoluminescence measurements with the temperature characteristic of scintillation efficiency between 10 and 350 K to determine the trapping levels that may influence the scintillation and phosphorescence properties of crystals of various compositions. Index Terms--[Lu.sub.2]Si[O.sub.5]:Ce, LSO, [(Lu,Y).sub.2]Si[O.sub.5]:Ce, LYSO, [(Lu,Gd).sub.2]Si[O.sub.5], LGSO, [(Lu,Y,Gd).sub.2]Si[O.sub.5]:Ce, LYGSO, oxyorthosilicate, scintillators, thermoluminescence.