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 Gd3Ga2.7Al2.3O12:Ce (GGAG:Ce) one were grown by the micropulling down method. Their optical, luminescence and scintillation characteristics were measured and mutually compared to optimize further the former compositions and reveal the reason of their lower scintillation performance with respect to GGAG:Ce. Correlated experiments of time-resolved luminescence and scintillation spectroscopies further completed by thermoluminescence glow curves measurement and electron paramagnetic resonance (performed on Gd-free Sc-admixed garnets) point to the Sc3+ situated at the dodecahedral site of garnet lattice as a dominating electron trap which creates a bottleneck in scintillation mechanism of the Sc-admixed garnets. It is mainly responsible for the degradation of scintillation efficiency in comparison with GGAG:Ce despite nearly the same effect 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 dodecaheral site are situated in the forbidden gap in the Sc-admixed garnets