Defects Identification and Effects of Annealing on Lu2(1-x)Y2xSiO₅ (LYSO) Single Crystals for Scintillation Application.

Samuel Blahuta,Eric Mattmann,Bruno Viana,Aurélie Bessière,Vladimir Ouspenski,Didier Gourier,Julien Lejay

doi:10.3390/ma4071224

Abstract

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.

Highlights

Ce-doped oxyorthosilicates are efficient scintillating materials used in various fields
For each LYSO:Ce sample grown by the Floating-Zone technique (FZ) technique, XRL emission spectra were first collected at room temperature (RT) and are shown in Figure 1(a), where the emission amplitude is given per surface unit
LYSO single crystals were prepared in order to investigate both the nature and the concentration of electronic defects

Summary

Introduction

Ce-doped oxyorthosilicates are efficient scintillating materials used in various fields. Lu2SiO5:Ce (LSO:Ce) was found to be very promising, especially for medical imaging applications such as Positron Emission Tomography (PET) [1,2]. Yttrium incorporation has a positive impact on the melting bath viscosity leading to easier crystal growth and a reduced amount of defects (vacancies, cracks), and is thought to enhance hole mobility in the material. The second part of this work deals with annealing treatments as a way to control point defects concentration. The effect of both oxidizing and reducing treatments on TL is presented

Nature of Electronic Defects

Effects of Annealing Treatments

Crystal Growth

Characterization

Conclusions