Structural, mechanical and light yield characterisation of heat treated LYSO:Ce single crystals for medical imaging applications

Abstract

International audienceFive single crystals of cerium-doped lutetium yttrium oxyorthosilicate (LYSO:Ce) grown by the Czochralski method were submitted to structural characterisation by X-ray (XRD) and neutron (ND) diffraction, scanning (SEM) and transmission (TEM) electron microscopy and energy dispersive microanalysis (EDS). The Ultimate Tensile Strength (UTS), the Young Modulus (YM) and the Light Yield (LY) of the samples were also measured in order to correlate the mechanical and the optical behaviour of the crystals with the characteristics of their microstructure. Two of the samples analysed were also heat treated at 300 °C for 10 h to evidence possible variations induced by the temperature in the optical and mechanical response of the crystals. Results showed that the mean compositional variations evidenced by the structural analyses do not affect the mechanical and optical behaviour of the samples. On the contrary, the thermal treatment could induce the formation of coherent spherical particles (size 10 to 15 nm), not uniformly distributed inside the sample, that strongly reduce the UTS and YM values, but it does not affect the optical response of the crystal. This latter result was attributed to the low value of the heating temperature (300 °C) that is not sufficiently high to induce annealing of the oxygen vacancies traps that are responsible of the deterioration of the scintillation properties of the LYSO:Ce crystals.This study was carried out in the framework of the Crystal Clear Collaboration (CCC)

On the photoelastic constants and the Brewster law for stressed tetragonal crystals

“…Crystal quality control and characterization requires fast and reliable experimental settings involving both destructive and nondestructive analyses, particularly in the case of scintillating crystal for high‐energy physics, biomedical application devices, etc (for a comprehensive recent review on scintillators, see, eg, Nikl and Yoshikawa): For instance, X‐ray can give structural information meanwhile the transmission electron microscopy gives precise information, but they are generally destructive and “not‐fast” techniques . Photoelastic analysis, instead, is generally nondestructive and “fast‐to‐perform” technique, which allows to detect the presence of internal stresses, which are generally associated to the presence of defects and to quality degradation; moreover, mechanical properties like the Young modulus or the ultimate tensile strength are necessary for devices design .…”

Quality Control and Structural Assessment of Anisotropic Scintillating Crystals

“…Ultimate tensile stress (UTS) and Young's modulus (YM) were measured in [7], [46]. Five of them were correlated to their structural and compositional condition [45]. Table 3, along with Figure 8, shows the UTS and YM values of samples.…”

Trends in Search for Bright Mixed Scintillators

“…Crystal slices of few nm thick with atomically clean surfaces are very difficult to prepare. Nevertheless, 1–3 μm size Gd‐ and Lu‐enriched domains in LGSO:Ce were evidenced by confocal luminescence microscopy, and ≈50–100 nm size Y content fluctuations in LYSO:Ce were observed by TEM combined with energy dispersive spectroscopy …”