Bridgman bulk growth and scintillation measurements of SrI 2 :Eu 2+ R. Hawrami a,n , J. Glodo a , K.S. Shah a , N. Cherepy b , S. Payne b , A. Burger c , L. Boatner d a Radiation Monitoring Devices, Inc., Watertown, MA 02472, United States b Lawrence Livermore National Laboratory (LLNL), Livermore, CA 94550, United States c Fisk University, Nashville, TN 37208, United States d Oak Ridge National Laboratory (ORNL), Oak Ridge, TN 37831, United States article info Available online 30 April 2013 Keywords: A2. Single crystal growth A2. Bridgman technique A2. Growth from melt B2. Scintillator material B2. Large diameter scintillator crystals B2. SrI 2 :Eu abstract Large diameter Bridgman growth of europium activated strontium iodide SrI 2 :Eu 2+ produces crystals with light yield of up to 115,000 ph/MeV with an excellent light yield proportionality. SrI 2 :Eu 2+ exhibits an outstanding energy resolution of better than 3% FWHM at 662 keV. Its emission is centered at 435 nm. The scintillation decays with a 1 μs time constant for small samples and up to 5 μs to larger crystals. This paper presents successful progress made in the vertical Bridgman crystal growth of SrI 2 :Eu 2+ and its scintillator properties. Large diameter, crack-free and transparent SrI 2 :Eu 2+ single crystals with diameters of 1 in., 1.3 in., 1.5 in. and 2 in. were all successfully grown. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The search for high light yield and large volume single crystal scintillators with a low-cost potential and high-energy resolution for gamma-ray spectroscopy has intensified in recent years due to a growing demand for nuclear isotope identifiers [1]. At present, scintillators are widely used in nuclear medicine, high-energy physics, astrophysics, security systems, geophysics, environmental control, and industrial applications. The most important scintillator parameters required by these applications are listed in Table 1 [2]. Within the last few years, a number of materials have displayed extremely promising properties, including LaBr 3 :Ce, LaCl 3 :Ce, elpasolites [3–4], and alkaline earth halides such as SrI 2 [5] or BaI 2 [6]. While LaBr 3 :Ce provides the highest energy resolution ∼2.8% at 662 keV, it is highly hygroscopic and its growth is still challenging. Elpasolites can provide very good energy resolution (e.g. 3% at 662 keV for Cs 2 LiLaBr 6 :Ce) but with the exception of Cs 2 LiYCl 6 :Ce they are not yet used commercially. Alkaline earth halides, and in particular iodides, are the newest crystal family being explored. They offer higher Z (ρ ¼ 5.1 g/cm 3 and Z eff ¼ 54.1 for BaI 2 ) and equivalent or higher light yields than LaBr 3 :Ce [7–8]. They require divalent activators, such as Eu 2+ or Yb 2+ , which have slower decay times when compared to Ce-doped scintillators. High light yields are observed with many iodide scintillators, such as CsI:Tl (65,000 ph/MeV) and LuI 3 :Ce (about 100,000 ph/MeV) [9]. Among the alkaline earth halides, SrI 2 :Eu 2+ scintillators are most promising in terms of properties and crystal growth. They are also closest to being a commercial product. SrI 2 :Eu 2+ proper- ties include [5] excellent non-proportionality [5], high light yield can be a function of size and impurities, and consequently excellent 2.8% energy resolution at 662 keV (FWHM) [5,6,10]. In this paper, we report on the successful growth and scintillation performance of single transparent, large diameter, crack-free Eu 2+ doped SrI 2 crystals. 2. Experimental performance Large diameter, transparent and crack-free single crystals with 1 in., 1.3 in., 1.5 in. and 2 in. diameters of strontium iodide (SrI 2 ) doped with europium iodide (EuI 2 ) have been successfully grown using the vertical Bridgman technique. Photographs of crystals grown at RMD are presented in Fig. 1. The crystal growth process starts by loading ultra dry SrI 2 powder with a purity of 99.99%, and ultra dry EuI 2 with a purity of 99.9% (supplied by Sigma Aldrich), into a freshly cleaned and pre-baked quartz ampoule within a glovebox of a pure and dry nitrogen atmosphere. The ampoule is sealed under a dynamic vacuum of 3.2 Â 10 -5 Torr. The crystals were grown within a two-zone, high temperature resistance vertical Bridgman furnace manufactured by the Mellen Company. Once grown, the crystals are processed in a moisture and oxygen free environment. They are cut into small samples as desired. Fig. 2 shows photographs of a 1 in. right cylinder of SrI 2 : Eu 2+ cut and processed at RMD. In order to prevent exposure to moisture, the crystals are successfully encapsulated. Fig. 3 shows photographs of packaged 1 in. Â 2 in. SrI 2 :Eu 2+ crystals at LLNL. Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2013.04.035 n Corresponding author. E-mail address: drh1980@gmail.com (R. Hawrami). Journal of Crystal Growth 379 (2013) 69–72