Compatibility of TiO2 reflective material with Ce:GAGG scintillators in harsh environments

In this study, we developed Ce:GAGG ceramic scintillators (containing 5 × 5 × 2 mm 3 Ce:GAGG single crystals) encapsulated by different light reflectors, namely, Teflon (400 μm), an enhanced specular reflector film (65 μm), and a titanium dioxide (TiO 2 ) reflector with different thicknesses and measured their γ-ray spectra under irradiation by a 137 Cs radioactive source. The reflectance of a 100-μm-thick (optimal thickness) TiO 2 layer demonstrated higher reflectance than other the TiO 2 reflectors of other thicknesses, and resulted in a high light-collection efficiency. To assess the temperature dependence of the reflectors, the samples were heated up to 300 °C in air. The measured reflectance decreased with increasing temperature, and the color of the reflector's surface changed. The observed variations in the surface morphology, measured by scanning electron microscopy, corresponded to the determined reflectance of the TiO 2 layer. Upon heating above 200 °C in air, the TiO 2 layer decomposed into other oxides, with a simultaneous increase in its surface porosity. By contrast, the Ce:GAGG single-crystal sample heated at 300 °C in vacuum showed only a negligible color variation, retained 80.3% of its initial reflectance, and exhibited an energy resolution of 12.8%. This result suggests oxidation as the potential cause of performance degradation. In addition, a TiO 2 layer covered with a heat-resistant epoxy isolated reflections from air, thus exhibiting a performance comparable to that of the without-epoxy sample. This result confirmed that a passivation layer may allow the use of reflectors at high temperatures. The results obtained in this study suggest that a TiO 2 layer can be used as a long-wavelength reflector in oxide and other types of scintillators for efficient radiation detection in harsh environments, including air-free environments, such as in aerospace, under vacuum conditions or in the presence of a protective passivation layer. • Compatibility of TiO 2 reflectors with Ce:GAGG in harsh environments studied. • Reflectance decreased with increasing temperature; optimal TiO 2 thickness: 100 μm. • Above 200 °C in air, the TiO 2 layer decomposed, and its surface porosity increased. • Vacuum-heated reflector retained 80.3 % of its initial reflectance at 300 °C. • Scintillator with vacuum-heated reflector showed a 12.8 % energy resolution.