Evidence and Consequences of Ce$^{4+}$ in LYSO:Ce,Ca and LYSO:Ce,Mg Single Crystals for Medical Imaging Applications

Abstract

Lu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2(1-x)</sub> Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2x</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> :Ce (10 at% Y) single crystals co-doped with Ca <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> and Mg <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> were prepared by the Czochralski technique. It is shown that co-doping leads to significant improvements of the scintillation performances. Afterglow following X-ray excitation is reduced down to 200 ppm after 20 ms and light yield is increased from 28,000 ph/MeV up to 34,000 ph/MeV under <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs-662 keV excitation. X-ray Absorption Near Edge Spectroscopy (XANES) was used to demonstrate that a significant part of the Ce ions are stabilized in the Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> oxidation state in co-doped crystals. A new scintillation mechanism involving Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> is proposed.