2130 IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 59, NO. 5, OCTOBER 2012 Improvement of Scintillation Properties in Pr Doped Al Scintillator by Ga and Y Substitutions Kei Kamada, Takayuki Yanagida, Jan Pejchal, Martin Nikl, Takanori Endo, Kousuke Tsutumi, Yutaka Fujimoto, Akihiro Fukabori, and Akira Yoshikawa Abstract— Ga Al single crystals were grown by the micro-pulling down ( -PD) method. Luminescence and scintillation properties were measured. The substitution phenomenon in the sites with and Al sites with Ga in garnet structure has been studied. 5d-4f emission within 300–400 nm accompanied by weak 4f-4f emission in 480–650 nm were observed in Ga 0–60 at.% substituted samples. Only 4f-4f emission was observed in Ga 80 at.% substituted sample. The light yield of Ga Al sample was almost the same as that of Cz grown Pr:LuAG standard. Two-component scintillation decay of 17.9 ns (93%) and 68.0 ns (7%) were obtained using the PMT and digital oscilloscope TDS5032B. Slower decay components were reduced by Ga and Y substitution in LuAG structure. Index Terms—Oxides, scintillator materials, scintillators, single crystal growth. I. INTRODUCTION P RASEODYMIUM ion exhibits fast 5d-4f emission in several host materials; such systems can be applied to obtain crystal scintillators with high figures of merit [1], [2]. Recently, our group intensively examined the scintillation prop- erties of several Pr-doped compounds [3]–[13]. Among those materials, Al was found with good scintillation properties due to high density (6.7 ), high light yield (approximately 20,000 photon/MeV), good energy resolution, and a very fast 5d-4f emission decay time (20 ns) [7]–[13]. On the other hand, aluminum garnet hosts such as Al (YAG) and LuAG have electron traps related to antisite defects [14]–[17]. A thermoluminescence (TSL) measurement in LuAG:Ce has identified electron traps associated with Manuscript received November 04, 2011; revised January 21, 2012; accepted February 03, 2012. Date of publication May 10, 2012; date of current version October 09, 2012. This work was mainly supported by JST Sentan and partially by a Grant in Aid for Young Scientists (B)-15686001, (A)-23686135, and Chal- lenging Exploratory Research-23656584 from the Ministry of Education, Cul- ture, Sports, Science and Technology of the Japanese government (MEXT). Par- tial financial support from Czech AV M100100910 and MSMT, no. 1M06002 projects is also gratefully acknowledged. K. Kamada, T. Endo and K. Tsutsumi are with Materials Research Laboratory, Furukawa Co., Ltd., 1-25-13, Kannondai, Tsukuba, Ibaraki, 305-0856, Japan (e-mail: k-kamada@furukawakk.co.jp). T. Yanagida, Y. Fujimoto, A. Fukabori and A. Yoshikawa are with IMR, To- hoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi, 980-8577, Japan. J. Pejchal and M. Nikl are with Institute of Physics, AS CR, Cukrovarnická 10, 162 53 Prague, Czech Republic. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TNS.2012.2191621 Al defects, which are responsible for glow curve peaks within 120–200 K [18]. Such shallow trapping states in the LuAG host slow down scintillation decay kinetics, and considerable amount of slower decay components was found [19]. Moreover, shallow electron traps ( 0.15 eV deep) have been recognized as responsible for temperature-dependent deterioration of scintillation yield in LuAG:Pr crystals regardless of the growth technology [20]. Due to the presence of such traps the room temperature yield of LuAG:Pr is decreased by about 30%. It has also been shown therein that it is possible to deactivate these traps using IR laser illumination of the sample, resulting in a corresponding increase of yield [20]. To optimize the performance of LuAG-based scintillator towards its intrinsic limits, understanding and control of such kind of defects through manufacturing technology are of crucial importance. Recently, it was found that in LuAG:Pr these trapping processes can be diminished by Ga substitution at the Al site, but slightly decreased light yield was observed as well [21]. Similar effects were obtained also in multicomponent garnets based on Ga Al formula where light yield exceeding 40,000 photon/MeV was obtained for optimized compositions [22]. transparent Al optical ceramic with scintillation response of about 90 ns at emission around 550 nm, prospective -excited light yield of about 11–16,000 photon/MeV, and density of 6.0 were reported. [23], [24] Interestingly, extremely high light yield up to 80,000 photon//MeV was reported for -excitation [24] In this paper, the Ga Al single crystals were grown by the micro-pulling down ( -PD) method. Lumi- nescence and scintillation properties were measured. The sub- stitution phenomenon in the sites with and the Al sites with Ga in garnet structure has been studied. II. MATERIALS NAD METHODS 1) Crystal Growth: A stoichiometric mixture of 4 N , , , Ga and Al powders (High Pu- rity Chemicals Co.) were used as starting material. The and sites were substituted by according to the formula of Ga Al . Single crystals of Pr:LYGAG were grown by the -PD method with an RF heating system. The y was 0.03 and additionally 2 mol% of Ga was added to compensate ignition loss. A schematic layout of the -PD growth apparatus is given in [25], [26]. Typical pulling rates were 0.05–0.07 mm/min and the diameter was around 3 mm. Crystals were grown from an Ir crucible under atmos- phere with, 2% of added to prevent evaporation of gallium 0018-9499/$31.00 © 2012 IEEE