Zr Doped GSO:Ce Single Crystals and Their Scintillation Performance

Cerium doped Gd
$_2$
SiO
$_5$
(GSO:Ce) single crystal is used as a scintillator for Positron Emission Tomography (PET). GSO:Ce has a good balance of every scintillation properties, but the only disadvantage is the decreasing light output by coloring caused by a small amount of Ce
$^4+$
in the crystal especially at higher concentration of Ce. In order to improve the scintillation performance, we have tried to grow co-doped GSO:Ce single crystal using conventional starting materials with additional impurities, and evaluate the scintillation performance. Zr doping is found to be effective in preventing coloring and in improving light output. Around 200 ppm Zr doped GSO:Ce have shown maximum light output which is about 20% larger than that of conventional GSO:Ce. This improvement can be explained by the fact that the amount of Ce
$^4+$
in the crystal might be changed to Ce
$^3+$
due to charge compensation caused by dopant Zr
$^4+$
in a Gd
$^3+$
site thereby decreasing the light absorption in the crystal.