GSAG:Ce scintillator: material optimization and intrinsic bottlenecks

Abstract

Several Sc-admixed garnet single crystals of the general composition (Gd,Sc)₃(Sc,Al)₅O₁₂:Ce and the well-established Gd₃Ga_2.7Al_2.3O₁₂:Ce (GGAG:Ce) one were grown using the micropulling down method. Their optical, luminescence and scintillation characteristics were measured and mutually compared to further optimize the former compositions and reveal the reason for their lower scintillation performance with respect to GGAG:Ce. Correlated experiments of time-resolved luminescence and scintillation spectroscopies further completed by thermoluminescence glow curve measurement and electron paramagnetic resonance (performed on Gd-free Sc-admixed garnets) indicate that Sc³⁺ is situated at the dodecahedral site of the garnet lattice as a dominant electron trap, creating a bottleneck in the scintillation mechanism of Sc-admixed garnets. This is mainly responsible for the degradation of scintillation efficiency in comparison with GGAG:Ce despite nearly the same effects of Sc and Ga in lowering the conduction band edge in these multicomponent garnets. Calculations of the electronic band structure confirm that the 3d energy levels of Sc³⁺ at the dodecahedral site are situated in the forbidden gap in Sc-admixed garnets.