Eric Mattmann

Defects Identification and Effects of Annealing on Lu 2(1-x) Y 2x SiO 5 (LYSO) Single Crystals for Scintillation Application

The nature, properties and relative concentrations of electronic defects were investigated by Thermoluminescence (TL) in Lu2(1-x)Y2xSiO5 (LYSO) single crystals. Ce and Tb-doped single crystals, grown by the Czochralski technique (CZ), revealed similar traps in TL. LYSO:Ce single crystals were grown by the Floating-Zone technique (FZ) with increasing oxygen concentration in the growth atmosphere. TL intensity is strongly dependent on the oxygen content of the material, and oxygen vacancies are proven to be the main electronic defects in LYSO. The effects of oxidizing and reducing annealing post-treatment on these defects were investigated. While oxidizing treatments efficiently reduce the amount of electronic defects, reducing treatments increase the amount of existing traps. In a thermally assisted tunneling mechanism, the localization of oxygen vacancies around the dopant is discussed. They are shown to be in the close vicinity of the dopant, though not in first neighbor positions.

Improved scintillation time response in (Lu0.5Gd0.5)2O3 : Eu3+ compared with Lu2O3 : Eu3+ transparent ceramics

The scintillation properties of two sesquioxides ceramics Lu2O3 : Eu3+ and (Lu0.5Gd0.5)2O3 : Eu3+ were studied. Both ceramics present comparable transparency and light yield whereas (Lu0.5Gd0.5)2O3 : Eu3+ showed an order of magnitude reduced afterglow in the 3–300 ms range. A thorough study of the location and behaviour of Eu3+ dopant ions at C2 and S6 sites of Lu2O3 and (Lu0.5Gd0.5)2O3 structures was carried out with low-temperature selective excitation of Eu3+. This revealed that (i) at both C2 and S6 sites, Eu3+ 4f–4f lifetime is shorter in (Lu0.5Gd0.5)2O3 : Eu3+ than in Lu2O3 : Eu3+, (ii) the host matrix (Lu0.5Gd0.5)2O3 as compared with Lu2O3 favours the location of Eu3+ at C2 site. As decay times of Eu3+ in C2 and S6 sites are 1.0 ms and 3.8 ms, respectively, the preferred occupation of C2 in (Lu0.5Gd0.5)2O3 : Eu3+ implies a much shorter decay time for (Lu0.5Gd0.5)2O3 : Eu3+ in the 3–20 ms range. Reduction of afterglow in the 20–300 ms range is illustrated by thermally stimulated luminescence peaks presenting a highly reduced intensity for (Lu0.5Gd0.5)2O3 : Eu3+ compared with Lu2O3 : Eu3+ implying reduced charge trapping defects in (Lu0.5Gd0.5)2O3 : Eu3+ ceramics.