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Large-size KCa0.8Sr0.2I3:Eu2+ Crystals: Growth and Characterization of Scintillation Properties Yuntao Wu, Adam Coleman Lindsey, Mariya Zhuravleva, Merry Koschan, and Charles L. Melcher Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b00631 • Publication Date (Web): 31 May 2016 Downloaded from http://pubs.acs.org on June 3, 2016
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Crystal Growth & Design
Large-size KCa0.8Sr0.2I3:Eu2+ Crystals: Growth and Characterization of Scintillation Properties Yuntao Wu,*,†,‡ Adam C. Lindsey,†,‡ Mariya Zhuravleva,†,‡ Merry Koschan,† and Charles L. Melcher†,‡ † ‡
Scintillation Materials Research Center, University of Tennessee, Knoxville, Tennessee 37996, USA Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
ABSTRACT: The newly developed KCa0.8Sr0.2I3:Eu2+ scintillator with 2.5% energy resolution at 662 keV shows great potential for use in gamma-ray spectroscopy applications, but progress toward large-size crystal growth has been hindered by cracking and inclusion problems. In this paper, we report a detailed study on the role of process variables of Bridgman growth, including grain selector designs, ampoule surface treatments, and temperature gradients. It was found that crystal cracking can be effectively prevented by using a carbon-coated quartz ampoule with a bent capillary. A high temperature gradient of 45°C/cm at the solid-liquid interface can positively contribute to the suppression of the formation of visible inclusions caused by constitutional supercooling. By using optimized growth parameters, high quality 22 mm diameter KCa0.8Sr0.2I3 single crystals doped with 0.5, 1 and 3 mol% Eu2+ and 38 mm diameter KCa0.8Sr0.2I3 single crystals doped with 0.5 mol% Eu2+ were grown by the Bridgman method. The scintillation properties, including radioluminescence, light yield, energy resolution, and scintillation decay, of ∅22 mm × 22 mm and ∅38 mm × 35 mm samples were also investigated. SECTION: Crystal Growth, Ampoule treatment, Temperature gradient, Scintillation, Alkali earth halides.
lem. As we know, grain competition and evolution is one of the most critical processes during self-seeding Bridgman crystal growth, but one of the disadvantages of self-seeding is the random growth orientation. Inappropriate seeding results in multiple grains, leading to fracture due to the coefficient of thermal expansion mismatch at grain boundaries. The importance of the grain selector design has been realized in the single crystal growth field, including using bent grain selectors for the growth of organic crystals 15 and inorganic halide crystals 12,16, and using angled or spiral grain selectors for the growth of superalloy turbine blades.17 Second, carbon-coated ampoules will be used in this work to resolve the surface cracking issue. This technique was proven to prevent sticking of the crystal to the crucible wall and minimize the stresses generated due to different thermal expansions of crucible and the crystal.16,18,19 Third, a high temperature gradient and a low translation rate will be utilized to suppress constitutional supercooling which may result in the formation of visible inclusions. In this work, we present a detailed study on the effect of process variables of Bridgman growth by engineering the grain selector geometry, ampoule surface treatment, and temperature gradient. The optimized growth parameters allow growth of large-size transparent KCa0.8Sr0.2I3:Eu2+ single crystals without cracks or visible inclusions. The paper is organized as follows: first, the effects of capillary geometry, ampoule surface treatment, and temperature gradient on the crystal quality will be investigated and discussed in detail; then, the scintillation properties of three ∅22 mm KCa0.8Sr0.2I3:Eu2+ single crystals doped with 0.5, 1, and 3 mol% Eu2+ grown by the self-seeding Bridgman method will be evaluated; finally, the scintillation properties of a ∅38 mm × 35 mm KCa0.8Sr0.2I3: 0.5 mol% Eu2+ single crystal will be also presented.
INTRODUCTION The Bridgman method (also known as the BridgmanStockbarger method) is widely used to grow single crystals which have low melting points and require atmosphere protection for various applications, such as nonlinear infrared crystals,1 semiconductor detectors,2,3 laser and ferro-/piezo-electric crystals,4 and inorganic scintillators 5-8. Driven by the increasing requirements of advanced medical imaging and homeland security applications, large diameter growth processes for many high figure-of-merit halide scintillators have been developed in recent decades, such as LaCl3:Ce3+,6 LaBr3:Ce3+,7 and SrI2:Eu2+ 8,9. In recent years potassium containing halide scintillators such as KSr2I5:Eu2+,10 KBa2I5:Eu2+,11 and KCaI3:Eu2+12 were explored and have achieved excellent performance, such as an energy resolution of
