β-Ga₂O₃ is a well-known semiconductor material for power devices and other applications. Recently, β-Ga₂O₃ has also been reported as a scintillator material with a light yield of approximately 8400 ph./MeV, scintillation decay time of <1 μs, and density of 6.44 g/cm³. In this study, 45 cm diameter β-Ga₂O₃ single crystals were prepared via oxide crystal growth using the cold crucible (OCCC) method under various oxygen partial pressures. In the OCCC method, as in the cold crucible method, a high frequency is applied directly to the oxide materials, which are heated and melted, and the melt is held by the outermost solid material itself that is cooled by water using a copper hearth. In the OCCC method, crystal growth is performed while rotating the seed crystal, as in the Czochralski method, to increase the crystal diameter. The optical properties and radiation responses of the crystals grown under various oxygen partial pressures were evaluated.

Ce-doped (Gd, La)2Si2O7 (Ce:La-GPS) scintillator was found to have a good light output of around 40,000 photons/MeV, while some other parameters have not been determined so far. In order to clarify the cause for such a high light yield, some physical parameters have been estimated in this work. The bandgap energy of Ce:La-GPS was evaluated to be over 7.13b0.03 eV for (Gd0.75, La0.25)2Si2O7. Although Ce:La-GPS had wider bandgap compared with other oxide scintillators, its light output was larger than values for some other scintillators. Since quantum yield of Ce:La-GPS was as high as around 0.8, the product of transfer efficiency and electron-hole pair generation efficiency was estimated to be around 0.9, which was higher than for the other scintillators. Thus, Ce:La-GPS was suggested to have high the product of transfer efficiency and/or electron-hole pair generation efficiency.