Fabrication and Photo-Physical Characterization of Ce-doped Gd3(Ga,Al)5O12 Transparent Ceramics

In recent years, oxide materials based on garnet structure are being investigated as very promising candidates in the field of scintillation because of their high density, good chemical stability, optical transparency, and the possibility to easily incorporate luminescent rare-earth ions. Several studies demonstrated that garnet crystals show high light yield and advantageous timing performances, which make them of interest for applications in medical imaging and high energy physics detectors [1]. Among synthetic garnets, Ce-doped gadolinium gallium aluminum garnet (GGAG:Ce) is a relatively new and interesting material. It is a mixed garnet that has displayed very good scintillation and luminescence properties: its high density enhances the interaction with ionizing radiation, and the presence of Gd provides a high cross section for thermal neutron capture [2]. GGAG:Ce preserves a crystalline cubic structure, which allows to produce it in the form of transparent polycrystalline ceramic [3] with favorable characteristics for optical applications such as lasers, LEDs, and scintillators. In this work, ceramic samples were produced by reaction sintering from commercial oxide powders: the mixed powders were pressed into pellets and sintered by a combined process of air sintering and hot isostatic pressing. The sintering process was carefully selected and the use of sintering additives was optimized to eliminate porosity, which is crucial to achieve a good optical transparency. Optical properties were studied by means of optical absorption spectroscopy, steady-state and time resolved photo- and radio- luminescence, and correlated to the fabrication process parameters. Moreover, trapping phenomena caused by the presence of point defects were investigated by wavelength resolved thermally stimulated luminescence in a wide temperature range (10 – 800 K); a significant persistent luminescence signal was also singled out and investigated as a function of temperature. The presence of point defects was also evidenced by the occurrence of a sensitization of the radio-luminescence signal as a function of increasing cumulated X-ray dose, related to a competitive process between traps and Ce recombination centers in free carrier capture. Finally, preliminary results on recently developed layered Y3Al5O12:Pr/Gd3(Ga,Al)5O12:Ce (YAG:Pr/GGAG:Ce) ceramics for particle detection and discrimination will be also reported. This work has been supported by H2020 European Institute for Innovation and Technology (EIT) SPARK project (16290) and H2020 Rise project INTELUM (644260). [1] M. T. Lucchini et al., Nucl. Instrum. Methods Phys. Res. A 816 (2016) 176-183 [2] J. Dumazert et al., Nucl. Inst. Methods Phys. Res. A 882 (2018) 53 [3] Y. Ye et al., Opt. Mater. 71 (2017) 23