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.

Scintillators are key components in high-energy x-ray detectors for x-ray computed tomography, which are applied in medical diagnosis, nondestructive testing, and security inspection. Scintillators in x-ray imaging are required to have both high spatial resolution and sensitivity; however, a trade-off between spatial resolution and sensitivity exists. To improve the sensitivity of a scintillator, its thickness must be increased; however, spatial resolution deteriorates with increasing thickness. Here, we developed a well-aligned Tb-doped GdAlO₃-αAl₂O₃ phase-separated scintillator fiber (PSSF) with a diameter of 1.25-μm by a micro-pulling-down method. The luminescence, scintillation, and imaging performances of a grown PSSF sample were evaluated. X-ray-induced radioluminescence measurements of the sample showed Tb³⁺ 4f–4f emissions in the wavelength range of 470–700 nm, and the maximum emission peak was at 550 nm. The contrast transfer function at 10 lp/mm was 82% for both 270 and 500 μm-thick PSSF samples. We calculated the luminescence index, which is the product of the scintillator’s light yield and sensitivity, of the samples and compared their values with commercially available conventional CsI:Tl columnar scintillators. The Tb-doped GdAlO₃-αAl₂O₃ PSSF exhibits higher contrast transfer function and luminescence index values at above 60 keV x-ray region compared with the tested conventional scintillators.

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.

The scintillation properties of Mg2+-codoped Lu0.6Gd2.4Al2Ga3O12:Ce (LGAGG:Ce,Mg) single crystal grown by Czochralski method are investigated. The light yield (LY), scintillation decay time and coincidence time resolution are presented in comparison with a GAGG:Ce,Mg reference crystal. The light yield of 26,200 photons/MeV obtained for LGAGG:Ce,Mg is lower than that of 39,600 photons/MeV for GAGG:Ce,Mg. Despite a lower LY value, time resolution of LGAGG:Ce,Mg is comparable to that of GAGG:Ce,Mg due to its faster scintillation decay time. LGAGG:Ce,Mg exhibits much faster afterglow decay and lower thermally stimulated luminescence intensity with respect to GAGG:Ce,Mg.