Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Effect of gamma-quanta and fast neutrons on color and emission centers in LuAG and LuAG:Pr crystals A.Kh. Islamov a,b , E.M. Ibragimova a , I.A. Khayitov a , R.R. Vildanov b,* , Kh.N. Kudratov a a Institute of Nuclear Physics, Uzbekistan Academy of Sciences, pos. Ulugbek, Tashkent, 100214, Uzbekistan b National University of Uzbekistan, Tashkent, 100174, Uzbekistan ARTICLE INFO Keywords: Color centers in LuAG Gamma and neutron irradiations Gamma-luminescence ABSTRACT Optical absorption, photo-excitation and photo- and gamma-luminescence spectra of nominally pure LuAG crystal and praseodymium doped LuAG:Pr scintillation detector were compared prior and after irradiations with 60 Co gamma-quanta in the dose interval 10 2 –10 6 Gy and reactor fast neutron fluencies 10 16 and 10 17 cm −2 accompanied by gamma radiation. The optical absorption of LuAG:Pr does not exceed 1 cm −1 in the range of 2.06–4.3 eV within the used gamma-dose interval. The gamma-luminescence of Pr 3+ activator at 4.0 eV de- creases by ~9% due to reabsorption by Cr 4+ and is stable within 10 3 –10 6 Gy. Fast neutron and gamma fluxes generate Frenkel pairs by elastic and inelastic mechanisms. Electron F- and F + -centers, hole O − centers, and also impurity Fe 3+ centers suppress by 50% the Pr 3+ emission by means of reabsorption after neutron fluency 10 16 cm −2 . The LuAG:Pr crystals can be recommended as a scintillator detector for applications involving neutron and gamma radiations at gamma-dose up to 10 6 Gy and fast neutron fluencies up to 10 12 cm −2 . 1. Introduction Single crystals of aluminum lutetium garnet Lu 3 Al 5 O 12 (LuAG) doped with praseodymium (Pr 3+ ) have a high density (6.7 g/cm 3 ), high light-output (near 20000 photon/MeV) and fast reading (20 ns) [1–4]. Such physical characteristics make this material very promising scin- tillation crystal for applications in medical imaging and high energy physics [5,6]. Under effect of high energy radiation it is important to keep stable optical and luminescent characteristics, i.e. radiation hardness, of scintillators up to a certain gamma (γ) radiation dose level of about 300 kGy [7]. Optical transparency in UV–vis range of nominally pure LuAG and praseodymium doped LuAG:Pr 3+ was found to decrease upon ionizing γ-quanta exposure due to localization of free charge carriers at the impurity and intrinsic defects followed by generation of color centers at doses 100–10 5 Gy [8–11]. The only short communication of Iwashita [12] reported about 13% decrease of the LuAG:Pr light output after 100 Gy exposure to 60 Co γ-quanta. Taking into account the prospective for improving the calorimeter luminosity, the γ-dose limit may increase to 10 6 Gy. So one should study not only the saturation level of color center accumulation, but also its effect on the activator luminescence spectra and the integral light output of LuAG and LuAG:Pr at high doses. Effects of fast neutron fluencies on optical absorption and luminescence of Y 3 Al 5 O 12 (YAG) garnet crystals were studied in details in Refs. [13–15]. It was shown, that unlike 60 Co gamma irradiation, where the color centers related to defects in O and Al sublattices reach to saturation at 10 3 –10 5 Gy, the color centers induced by the neutron irradiation up to 10 19 cm −2 do not saturate [13–15]. The contribution from dopants to the defect color centers was not found, and the lumi- nescence intensity decreased only above 10 18 cm −2 . There are no data on effect of fast neutrons on the optical response of LuAG:Pr and the host matrix LuAG. This research was aimed at comparative study of the optical ab- sorption and luminescence spectra of nominally pure LuAG and doped with Pr 3+ ions exposed to fast neutron and gamma-quanta fluxes, for identification of the intrinsic and radiation induced defects in Lu, Al and O sublattices and their influence on the luminescence of Pr 3+ ions. 2. Materials and methods Nominally pure LuAG and doped LuAG:Pr 3+ (Pr concentration 0.22 mol.%) single crystals were grown in argon atmosphere by Czochralski method at Furukawa Co. Ltd, Japan. For doing optical measurements, polished plates were prepared with area 4 × 4 mm 2 and thickness 1 mm. The samples were irradiated with 1.17 and 1.35 MeV γ-quanta from 60 Co source and the dose rate of 0.8 Gy/s in the dose range https://doi.org/10.1016/j.optmat.2019.109344 Received 28 May 2019; Received in revised form 21 August 2019; Accepted 22 August 2019 * Corresponding author. E-mail address: ramvild@gmail.com (R.R. Vildanov). Optical Materials 96 (2019) 109344 0925-3467/ © 2019 Elsevier B.V. All rights reserved. T