Cerium-Doped Orthophosphate Scintillators

Abstract

ABSTRACTCerium-doped lutetium orthophosphate (LuPO4:Ce) is one of the most promising new scintillator materials. In this paper we report on the effects of total or partial replacement of Lu by Yb. When not doped with Ce, crystals of YbxLu1-xPO4 scintillate rather poorly, the emission being due to the Yb charge transfer transition. Activation with Ce reduces the light output from Yb even further, while correspondingly the addition of Yb to LuPO4:Ce also degrades that material's scintillation performance. We suggest that the nonradiative decay of the (Yb2+-Ce4+) charge transfer state is responsible for the mutual quenching of these ions. The differences in performance of LuPO4:Yb and LuPO4:Ce indicate that energy transfer mechanisms ordinarily associated with materials containing molecular anionic groups may not be quite sufficient to explain the results. Suggestions are presented that under γ-excitation the lattice-to-ion energy transfer in orthophosphates is accomplished by sequential capture of charge carriers rather than the more conventional mechanism of exciton hopping between molecular groups.