A number of halide and oxide scintillator materials have been developed and they are applied to various fields such as astronomy, medical imaging, and homeland security. Although halide scintillators, such as Tl:NaI, Tl:CsI and Ce:LaBr₃, have high light outputs of more than 30,000 photons/MeV, they have hygroscopic nature. On the other hand, most oxide scintillators don’t have hygroscopic nature. Ce:Gd₂Si₂O₇ (Ce:GPS) had a good light output of 30,000 photons/MeV and FWHM energy resolution of 6.0% at 662 keV at room temperature. However, according to the previous report [1], Ce:GPS crystals need to be grown with heavy Ce-doping (approximately, 10 mol%) in order to stabilize the crystal growth process. Such high Ce-concentration would lead to lower light output because of self-absorption or concentration quenching. The main reason is the fact that Gd₂Si₂O₇isn’t congruently melt. When the chemicals with stoichiometric composition is melted, initial melt has apatite phase. Recently, we found substitution of La into Gd site gives positive effect of the phase stability of this pyrosilicate [2]. However, the ratio of La isn’t optimized. In this study, variety of combination of x and y in Gd_2-x-yLa_xCe_ySi₂O₇ are prepared and the optimum ratio of La into Gd site are investigated. Gd₂O₃, La₂O₃, CeO₂ and SiO₂ with 99.99% purity are used as starting chemicals. Ce:La-GPS single crystals were grown by the Micro-Pulling Down (m-PD) method with RF heating system using Ir crucible. The growth rate was 3-5mm/h and the atmosphere was under N₂. The Iridium rod was used as a seed in the first growth and the seed was gotten from this grown crystal.

The relationship between the amount of La and initial phase and structure will be discussed. Crystal growth attempts from the different x and y melt composition will be made and discussed with this relation. After thecrystal growth, photoluminescence, PL decay, radioluminescence, pulse height spectra and scintillation decay were measured and will also be reported taking the relation into account.

Reference

1. S. Kawamura, J. H. Kaneko, M. Higuchi, et.al., IEEE Trans. Nucl. Sci. 54, (2007) 1383.

2. A. Suzuki, S. Kurosawa, A. Yoshikawa, et. al., Appl. Phys. Express 5 (2012) 102601.

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