Engineering LYSO Single Crystals for Performance

LYSO:Ce for Positron Emission Tomography (PET)

LYSO:Ce has a set of interesting features, including high density, gamma emissions which are suitable for PMTs, and a high quality scintillation performance. It was grown using the Czochralski method. It could be improved, however, by a quicker Decay Time and lower Afterglow.

PET scanner ring

Czochralski growth

LYSO Performance Enhancement by Co-Doping

Its higher output of light and reduced afterglow improves its level of performance. Its Ce⁴⁺ stabilization must be considered, and is proved with XANES¹.

As a result of the stabilization of Oxygen vacancies, trapping is less efficient. The compensation mechanism can be altered using Ce⁴⁺, however.

The uncontrolled co-doping contact results in unstable crystal growth. This produces a spiral shaped, meaning that cracks may be more liable to occur and production yield is low. This may be explained by a reduced surface tension, as a result of high impurities or doping.

Standard co-doping is not suited to industrial production as poor performance results from a low co-doping content. Furthermore, unstable crystal growth results from a high co-doping content.

Stabilization of Ce⁴⁺ centers

Significantly suppressed afterglow

Reduced decay time

Engineered LYSO for Large Scale Industrial Production

The composition’s progressive optimization can be achieved by modifying the characteristics of crystal growth. This is achieved via the precise control of both co-dopants' and activator-dopants' concentrations.

During the growth, the oxidizing agent (such as MOx) can be used. This is a source of oxygen, and can be used for decomposition in the melted bath. The number of defects related to oxygen can be reduced without producing undesired contamination.

There are several consequences for the growth. Surface tension is increased, crystal growth is stabilized (even at sizeable diameters), cracking is eliminated, and the quality of the crystals improves.

Large Diameter Controlled Growth

Performance of Engineered LYSO

Consistently Improved Timing Resolution

Timing Resolution of Engineered LYSO*

*Measured with 4x4x20 mm LYSO pixels, ends-on coupling Two Photonis XP20Y0 PMT’s @ -900 V, 100 µCi ²²Na source

Conclusions and Perspectives

There are limitations to standard co-doping which can be improved. Afterglow, Decay Time, and Light Yield could all be improved, and Ce⁴⁺ could be stabilized for charge compensation. Unstable crystal growth results from uncontrolled co-doping, and co-doping is not able to be applied directly to industrial production.

LYSO can be engineered for industrial production as there isn’t any pollution to impact upon scintillation. The oxidizing agent method can be used and doping concentrations can be controlled. This opens up a range of opportunities for the preparation of scintillators.

Full production sizes of engineered LYSO are available. Decay Time has been reduced to 34 ns and Light Yield is over 40000 Ph/MeV (gamma 662 keV). The Afterglow of commercial GOS ceramics is similar to that of engineered LYSO, providing a for the CT or PET systems’ markets.

References

1. S. Blahuta, A. Bessière, B. Viana, P. Dorenbos and V. Ouspenski, IEEE Transactions On Nuclear Science 60, 3134-3141 (2013).
2. M. Spurrier, P. Szupryczynski, H. Rothfuss, K. Yang, A. A. Carey and C. L. Melcher, J. Crystal Growth 310, 2110-2114 (2008).

This information has been sourced, reviewed and adapted from materials provided by Saint-Gobain Crystals.

For more information on this source, please visit Saint-Gobain Crystals.