Journal of the Korean Physical Society, Vol. 75, No. 12, December 2019, pp. 962∼967 Investigation of Optical Properties of Ceramic Ce:GAGG by High Temperature Annealing Chansun Park, Muhammad Nasir Ullah and Chanho Kim Department of Bio-convergence Engineering, Korea University, Seoul, 02841, Korea Shinhaeng Cho Chonnam National University Medical School, Gwangju, 61186, Korea Jung-Yeol Yeom ∗ Department of Bio-convergence Engineering, Korea University, Seoul, 02841, Korea and School of Biomedical Engineering, Korea University, Seoul, 02841, Korea (Received 9 September 2019; revised 21 October 2019; accepted 29 October 2019) An as-fabricated cerium-doped ceramic scintillator Gd3Al2Ga3O12 (Ce:GAGG) was thermally annealed at different temperatures. The light output and energy resolution of the scintillators were measured before and after thermal treatment. The effect of thermal annealing in the air at high temperature (at 1000 ◦ C for 5 hours) deforms the microstructure by mitigating oxygen vacancies of the ceramic scintillator. This has been proven by XPS study that showed the existence of oxygen vacancies and subsequent decrease of oxygen deficiency amid annealing treatment that led to an output signal increase. The diffusion ability of oxygen atoms by annealing played a key role in compensating for defect sites. In this study, by controlling thermodynamic conditions, the light output was enhanced by ∼30.4% and the energy resolution improved by ∼2.4% after annealing at 1000 ◦ C in the air. PACS numbers: 29.30.Kv, 29.40.Mc, 61.72.Cc, 81.05.Je Keywords: Scintillator, Light output, Energy resolution, Gamma-rays, X-ray Photoelectron Spectroscopy DOI: 10.3938/jkps.75.962 I. INTRODUCTION Inorganic scintillators are being used in many applications such as medical imaging and home- land security [1–3]. Inorganic scintillating crystals such as (Lu,Y) 2 SiO 5 :Ce (LYSO), Gd 2 SiO 5 :Ce (GSO), Bi 4 Ge 3 O 12 (BGO), etc. frequently used in such appli- cations are grown by conventional single-crystal growth methods like Czochralski method, Bridgman method, Floating zone method, etc. [4]. Recently, transparent oxide ceramic scintillators such as SrI 2 , Lu 3 Al 5 O 12 :Pr (Pr:LuAG), Y 3 Al 5 O 12 :Ce (Ce:YAG), (Gd, Y) 3 (Ga, Al) 5 O 12 :Ce (Ce:GYGAG) have also been fabricated. These non-hygroscopic ceramics offer higher spectral performances, better stopping power due to their high atomic number while allowing large scale production (cost reduction) compared to single-crystals [5–9]. One of them, the cerium-doped ceramic Gd 3 Al 2 Ga 3 O 12 (Ce:GAGG) could be a competitive candidate for some applications [10,11]. ∗ E-mail: jungyeol@korea.ac.kr Meanwhile, the poorer transparency of ceramic scin- tillators compared to the single-crystal scintillators re- stricts the transportation of scintillation photons to the photodetectors. This affects light collection at the pho- tosensor [12], especially when thicker scintillators are re- quired to detect high energy x-ray or gamma radiation. That is inherent problems associated with microstruc- ture inevitably degrade scintillators’ luminescence and deteriorate their optical properties. The occurrence of lattice distortions or point defects (vacancies, impurity ions) on the surface of scintillators have been consid- ered as obstacles for signal transportation and detection due to the delay in the migration of electrons and holes through the detectors [13]. The creation of such defects results in the degradation of scintillation light collection efficiency. Since the formation of the microstructures is inherent to the fabrication process, numerous efforts to alter its structures have been introduced [14]. For exam- ple, rectifying the composition concentration imbalance in the vicinity of point defects by thermal annealing have shown to give a better optical performance in related studies [15–18]. The light output from a scintillator is a vital characteristic that determines the performance of pISSN:0374-4884/eISSN:1976-8524 -962- c 2019 The Korean Physical Society