Speaker
Description
Detectors of ionizing radiation are widely used in the medical (CT, PET or PEM), homeland security fields and in scientific applications as electromagnetic calorimeters at CERN [1,2]. After 2000 year, the fast and efficient LuAG:Ce single crystal of garnet structure was developed [1] and its latest generation reached L.Y. ~27000 ph/MeV [2]. LuAG:Ce crystals grown by the Czochralski method from high temperature melt (~2020 oC) do show deteriorated scintillation performance due to “antisite defects” (AD) constituted by the Al3+ ions at Lu3+ lattice sites [1]. On the other hand, transparent LuAG:Ce optical ceramics prepared by a solid state reaction method with the use of MgO sintering aid do not usually show these defects [2,3]. The sintering of ceramics is provided in vacuum on isostatically pressed samples at temperature around 1800 oC but no liquid phase arises during the sintering. These ceramics can reach (i) better homogeneity of dopants (or codopants) and also (ii) larger, tailored size resulting in less expensive technology [3]. The development of LuAG:Ce optical ceramic materials started in the first decade of 21st century. Nowadays, its highest prompt (shaping time less than 2 µs) L.Y. ~25000 ph/MeV was observed [2], but the highest values (shaping time 10 µs) of L.Y. ~ 30700 ph/MeV was observed on LuAG:Ce,Ba,Mg ceramic, ~29000 ph/MeV at LuAG:Ce,Li and LuAG:Ce,Ba ceramics and ~28000 ph/MeV at LuAG:Ce,Mg. The latter ceramic sample exhibits the best photopeak energy resolution ~5 % at 662 keV [2] while other ceramics exhibit resolution around 8 % comparable to that of LuAG:Ce crystal. Scintillation decays of the LuAG:Ce ceramic samples (with codopants and nonstoichiometric ones) consist of fast and slow decay component parts and the best nonproportionality (~a decrease to 80 % at 10 keV from 100 % at 662 keV) is found at LuAG:Ce nonstoichiometric ceramics. Results observed on various LuAG:Ce ceramics will be discussed under the model presented in [2] where the presence of Ce3+ and Ce4+ was verified from XANES spectra but various defects can be present due to Mg2+, Li+ and Ba2+ codopants.
We will present a review of scintillation properties (L.Y’s, energy resolutions, non-proportionality and scintillation decays) of LuAG:Ce ceramics prepared from (i) stoichiometric or nonstoichiometric (both an excess or deficiency of Lu) compositions, (ii) with Mg2+codopant and (iii) with other codopants as Li+ and Ba2+.
[1] M. Nikl, A. Yoshikawa et al. Prog. Cryst. Growth Charact. Mater. 50 (2013)
41-72.
[2] S. Liu, J.A. Mares, X. Feng et al. Adv. Opt. Mater. 4 (2016) 731-39.
[3] S. Liu, X. Feng, Y. Shi et al. Opt. Mat. 36 (2014) 1973-77.
