The effect of co-doping on the growth stability and scintillation properties of lutetium oxyorthosilicate

Lutetium oxyorthosilicate (LSO) is a well-known scintillator that is widely used for gamma-ray detection in positron emission tomography (PET) as well as in other applications. LSO is typically doped with 0.05-0.5% Ce while controlling other impurities at low levels, but recent research has begun to explore the manner in which various co-dopants may influence scintillation properties. We have found that some co-dopants, particularly Ca, have a desirable impact on scintillation, leading to improvements in both light yield and decay time that are related to co-dopant concentration. However, it has been observed that in concentrations high enough to optimize scintillation properties some of these co-dopants can have a pronounced negative effect on the growth stability in Czochralski growth systems. We have observed acentric growth shortly after reaching full diameter despite no obvious change in thermal gradients or convective flow. Visual observations of the liquid meniscus suggest that Ca co-doping significantly reduces surface tension; one possible explanation is that the resulting enhanced Marangoni flow is responsible for the unstable growth behavior. Fortunately, we have found that an additional co-dopant can be used to restore adequate surface tension and thus stabilize growth with no negative impact on the scintillation properties of the crystal, To date, the most effective co-dopant for this purpose is Zn, when introduced in concentrations greater than that of Ce and Ca. (c) 2007 Elsevier B.V. All rights reserved.