Cerium activated mixed lutetium/gadolinium- and aluminum/gallium-based garnets have great potential as host scintillators for medical imaging applications. (Gd,Lu)<sub>3</sub>(Al,Ga)<sub>5</sub>O<sub>12</sub>:Ce and denoted as GLuGAG feature high effective atomic number and good light yield, which make it particularly attractive for Positron Emission Tomography (PET) and other γ-ray detection applications. For PET application, rapid decay and good timing resolution are extremely important. Most Ce-doped mixed garnet materials such as GLuGAG:Ce, have their main decay component at around 80 ns. However, it has been reported that the decays of some single crystal scintillators (<i>e.g</i>., LSO and GGAG) can be effectively accelerated by codoping with selected additives such as Ca, Mg and B. In this study, transparent polycrystalline (Gd,Lu)<sub>3</sub>(Al,Ga)<sub>5</sub>O<sub>12</sub>:Ce ceramics codoped with Ca or Mg or additional Ce, were fabricated by the sinter-HIP approach. It was found the transmission of the ceramics are closely related to the microstructure of the ceramics. As the co-dopant levels increase, 2<sup>nd</sup> phase occurs in the ceramic and thus transparency of the ceramic decreases. Ca and Mg co-doping in GLuGAG:Ce ceramic effectively accelerate decays of GLuGAG:Ce ceramics at a cost of light output. However, additional Ce doping in the GLuGAG:Ce has no benefit on improving decay time but, on the other hand, reduces transmission, light output. The mechanism under the different scintillation behaviors with Mg, Ca and Ce dopants are discussed. The results suggest that decay time of GLuGAG:Ce ceramics can be effectively tailored by co-doping GLuGAG:Ce ceramic with Mg and Ca for applications with optimal timing resolution.
Lanthanide gallium/aluminum-based garnets have a great potential as host structures for scintillation materials for
medical imaging. Particularly attractive features are their high density, chemical radiation stability and more importantly,
their cubic structure and isotropic optical properties, which allow them to be fabricated into fully transparent, highperformance
polycrystalline optical ceramics. Lutetium/gadolinium aluminum/gallium garnets (described by formulas
((Gd,Lu)3(Al,Ga)5O12:Ce, Gd3(Al,Ga)5O12:Ce and Lu3Al5O12:Pr)) feature high effective atomic number and good
scintillation properties, which make them particularly attractive for Positron Emission Tomography (PET) and other γ-
ray detection applications. The ceramic processing route offers an attractive alternative to single crystal growth for
obtaining scintillator materials at relatively low temperatures and at a reasonable cost, with flexibility in dimension
control as well as activator concentration adjustment.
In this study, optically transparent polycrystalline ceramics mentioned above were prepared by the sintering-HIP
approach, employing nano-sized starting powders. The properties and microstructures of the ceramics were controlled by
varying the processing parameters during consolidation. Single-phase, high-density, transparent specimens were
obtained after sintering followed by a pressure-assisted densification process, i.e. hot-isostatic-pressing. The transparent
ceramics displayed high contact and distance transparency as well as high light yield as high as 60,000-65,000 ph/MeV
under gamma-ray excitation, which is about 2 times that of a LSO:Ce single crystal. The excellent scintillation and
optical properties make these materials promising candidates for medical imaging and γ-ray detection applications.
Lutetium oxyorthosilicate (Lu<sub>2</sub>SiO<sub>5</sub>:Ce<sup>3+</sup>, commonly known as LSO) is a scintillator of choice for medical imaging
applications such as Positron Emission Tomography (PET) because of its high light output, high gamma ray stopping
power and fast response. In the current study, phase-pure LSO ceramics were obtained with a high degree of optical
transparency and excellent scintillation properties. These LSO optical ceramics were prepared by combining
nanotechnology with a sinter-HIP approach. We found that the densities of the LSO ceramics increased with
increasing sintering temperature, which corresponds to a systematic decrease in porosity as found by SEM
examination. The residual pores were found to segregate at grain boundaries after sintering, and were essentially
removed by subsequent hot isostatic pressing (HIPing), which raised the density to essentially the value characteristic
of the single crystal and produced polycrystalline LSO ceramics with a high degree of transparency. Under
excitation a <sup>22</sup>Na source such specimens displayed a light output as high as 30,100 ph/MeV. The LSO ceramics
showed an energy resolution of 15% (FWHM) at 662 keV (<sup>137</sup>Cs source) and a fast scintillation decay of 40 ns due to
the 5d → 4f transition of Ce<sup>3+</sup>. The excellent scintillation and optical properties make LSO ceramic a promising
candidate for future gamma-ray spectroscopy as well as medical imaging applications.