Speaker
Description
Currently, CsI:Tl and Gd2O2S:Tb (GOS) were recent commercially available scintillators for X-ray imaging. In this applications improvements of sensitivity and special resolution are required to obtain much fine morphological information. To improve sensitivity and special resolution, increase of thickness of scintillator plates or discover of new heavier scintillation materials were necessary. Up to now our group reported submicron-diameter phase-separated scintillator fibers (PSSFs) using directionally solidified eutectic (DSE) systems for higher resolution X-ray imaging. CsI/NaCl, GAP/α-Al2O3 [1] and LiF/ CaF2/LiBaF3 [2] have been already reported as PSSFs.
HfO2 doped with Eu has attracted attention due to its high density of 9.7 g/cm3, a high effective atomic number (Hf:72) and negligible intrinsic background. Light yield of Eu:HfO2 powders was reported to be 30000-31000 photons/MeV. Most recently fabrication of Eu:HfO2/α-Al2O3 eutectics and observation of its PSSFs structure were reported. HfO2 itself and HfO2 compounds have generally high melting temperatures of more than 2700 °C. HfO2 based DSE growth was firstly reported at the eutectic point blow 2000 °C. However, The Eu:HfO2/α-Al2O3 eutectics showed relatively week Eu3+ 4f4f emission comparing to the GOS standard[3].
In this study, Eu doped and Y substituted HfO2/α-Al2O3 were investigated as a scintillator material for X-ray imaging application. Here, Y substitution effect on crystal structure and luminescence properties in HfO2 were investigated. Crystal growth was performed by the µ-PD method for the eutectic composition, whose melting point is at significantly lower temperatures than that of HfO2 itself.
Eu doped (Hf,Y)O2/Al2O3 eutectics were fabricated with c-axis oriented a-Al2O3 seed by the -PD method. Fiber-like eutectic structure were observed along the growth direction. Y substitution effect on crystal structure and luminescence properties in HfO2 were investigated.Y=20 and 30% subsutituted (Hf,Y)O2/Al2O3 showed cubic (Hf,Y)O2 and a-Al2O3 phases. Y=40% showed thirdly perovskite phase. Broad Eu2+ 4f5d emission peaking at 480nm was observed in the Y 3% sample. Photoluminescence decay time of the Eu2+ 4f5d transition was 8.93 ms 77%, 25.6 ms 16%, 326 ms 7%.
References
[1] Y.Ohashi, A.Yoshikawa, Y.Yuui, A.Yoshikawa, T.Den, App. Phy. Lett. 102, (2013) 05197.
[2] K. Hishinuma Kosuke, K. Kamada, S. Kurosawa, A.kihiro Yamaji Y. Ohashi,, Y. Yokota, A. Yoshikawa, Jpn. J. Appl. Phys. 54 (2015) 04DH04
[3] K.Kamada , K. Hishinuma, S. Kurosawa, A. Yamaji, Yasuhiro Shoji, J. Pejchal, Y.Ohashi, Y. Yokota, and A. Yoshikawa, J.of Rare Earths 34(2016) 796–801
