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The presence of impurities and dopants (or codopants) can influence solute transport at the solid-liquid interface and its stability during bulk crystal growth, which ultimately affect the crystal uniformity. Codoping with Ca 2+ can significantly improve the performance of Lu 2 SiO 5 :Ce single crystals, well-known scintillators for nuclear medical imaging, albeit at the expense of growth stability due to surface tension reduction. However, an understanding of the correlation between crystal growth properties and radial performance uniformity in Czochralski-grown LSO:Ce, Ca single crystals is still lacking. In this work, we reveal this essential correlation by studying the roles of Ca 2+ concentration on the radial distribution of stable Ce 3+ ions and oxygen vacancy (V O ) related defects as well as solute transport at the solid-liquid interface. Through mapping of optical and scintillation properties across cross-sections of 0.1 at% and 0.4 at% Ca codoped boules and the defect formation energies derived from density functional theory (DFT) calculations, a direct link between Ca 2+ ions, stable Ce 3+ or Ce 4+ ions, and {Ca Lu  + V O } complex defects is established. The light yield enhancement in Ca 2+ codoped LSO:Ce single crystals is attributed to the dissociation of spatially correlated Ce ions and oxygen vacancies. Based on the quantitative comparison of photoluminescence (PL) and radioluminescence (RL) emissions from Ce1 (seven-coordinated) and Ce2 (six-coordinated) sites, the preferential occupation of stable Ce 4+ is believed to depend on the concentration of stable Ce 4+ . The underlying causes of symmetry and variation in the radial distribution of optical and scintillation properties, as consequences of Ca 2+ distribution, are discussed from the perspective of crystal growth. [ABSTRACT FROM AUTHOR]

Many single crystal scintillators, such as Lu 3 Al 5 O 12 , have intrinsic defects that impede their performance. In addition to doping with activators such as cerium, codoping can be used to improve the scintillation properties of a variety of scintillators. In particular, boron has been shown to improve the light yield, energy resolution, and self-absorption of other garnet scintillators, such as GGAG, when incorporated into the lattice via codoping. In this study, single crystals of LuAG: 0.2 at.% Ce codoped with varying concentrations of boron were grown via the Czochralski method at a rate of 1.2 mm/h. Results will show the effect boron codoping has on the scintillation properties of LuAG: Ce, including light yield, decay time, and self-absorption. [ABSTRACT FROM AUTHOR]

Luminescence and scintillation properties of Bi 3+ , Sb 3+ , and Eu 2+ -doped LaI 3 and LaBr 3 were explored. Out of the three dopants investigated, Eu 2+ was the most promising new activator for small-bandgap LaX 3 (X = Br, I) and was further studied in the mixed-halide LaBr 3−x I x . Crystals were grown from the melt using the vertical Bridgman method. LaBr 3 :Eu 2+ 0.5% (mol) had the most favorable scintillation properties with a light output of 43,000 ph/MeV and 6% energy resolution at 662 keV. Performance of LaBr 3−x I x :Eu 2+ worsened for most samples as iodide concentration was increased. Room-temperature scintillation of LaI 3 :Eu 2+ 0.1% and 0.5% was observed and is the first case of room-temperature emission reported for doped LaI 3 . [ABSTRACT FROM AUTHOR]

The distorted-perovskite scintillator materials CsCaI 3 :Eu and CsSrBr 3 :Eu prepared as single crystals have shown promising potential for use in radiation detection applications requiring a high light yield and excellent energy resolution. We present a study using high temperature powder X-ray diffraction experiments to examine a deleterious high temperature phase transition. High temperature phases were identified through sequential diffraction pattern Rietveld refinement in GSAS II. We report the linear coefficients of thermal expansion for both high and low temperature phases of each compound. Thermal expansion for both compositions is greatest in the [0 0 1] direction. As a result, Bridgman growth utilizing a seed oriented with the [0 0 1] along the growth direction should be used to mitigate thermal stress. [ABSTRACT FROM AUTHOR]

We investigate the multi-ampoule growth at 25 mm diameter of ternary iodide single crystal scintillator KCaI 3 :Eu using the randomly oriented self-seeded Bridgman method. We compare scintillation performance between cubic inch scale crystals containing small variations of low nominal europium concentrations previously shown to balance light yield with self-absorption in the host crystal. Growth conditions were optimized in the developmental furnace and four 2 in 3 KCaI 3 :Eu crystals were grown simultaneously producing a total of six 25 mm × 25 mm cylinders. Small variations in activator concentration did not result in significant performance differences among the six measured crystals. A range of energy resolutions of 3.5–4.7% at 662 keV was achieved, surpassing that of NaI:Tl crystals commonly used in spectroscopic detection applications. The function and basic design of the multi-ampoule furnace as well as the process of growing single crystals of KCaI 3 is included here. [ABSTRACT FROM AUTHOR]

KCaI 3 :Eu crystals have been identified as very promising for use in spectroscopic detector applications related to nuclear nonproliferation and domestic security efforts. Initial studies have shown for small crystals a few mm 3 in size with 3% europium dopant concentration, a high light yield of >70,000 ph/MeV and energy resolution of ≈3% at 662 keV is attainable which is comparable with the highest performance scintillators discovered. In this work, single crystals of KCaI 3 with a range of Eu 2+ doping between 0 and 5 at% substituting for Ca 2+ were grown at 22 mm diameter and their performance for gamma-ray spectroscopy studied. Comparisons among crystals approximately Ø22 mm×22 mm (8.4 cm 3 or ≈0.5 in 3 ) provide a more accurate understanding of how scintillation performance changes with Eu doping and increased crystal size. KCaI 3 in the undoped form is shown to be a highly efficient intrinsic scintillator with a defect-related emission at 404 nm which coexists with the Eu 2+ 5d–4f emission in low dopant concentrations and is completely re-absorbed in more heavily doped crystals. For larger crystals, effects from self-absorption due to Eu activation become more evident by a near doubling of decay time for 0.5 in 3 crystals as the activator is increased from 0.5 to 5.0 at% Eu. Comparisons of pulse-height spectra obtained for Ø22 mm×22 mm cylinders with varying Eu concentration suggests best performance is achieved using lower Eu additions closer to 0.5–1.0 at%. Using a modified crystal packaging featuring an offset reflector geometry, 0.5 in 3 crystals of KCaI 3 :Eu can attain under 4% energy resolution at 662 keV. [ABSTRACT FROM AUTHOR]

The crystal growth of CsSrBr 3 : Eu with improved energy resolution for use in gamma-ray detection applications is reported. CsSrBr 3 boules doped with 5% Eu were grown by the vertical Bridgman method in quartz ampoules of 17 mm and 22 mm diameter. It was observed that the addition of an excess of CsBr in the melt improved the optical transparency and energy resolution of the scintillator crystals. The energy resolution of the gamma-ray spectra recorded with crystals measuring ø 22 mm×15 mm was 7.4% at 662 keV (for a crystal with non-optimized stoichiometry) and 6.2% at 662 keV (for a crystal with optimized stoichiometry i.e. excess CsBr in the melt), which is a significant improvement over previous reports. Temperature dependent powder XRD measurements were also carried out to study the solid–solid phase transition which occurs as the crystals are cooled after growth. [ABSTRACT FROM AUTHOR]

Abstract: The current work describes two new Eu2+-activated scintillator materials, CsCaI3:Eu and CsCaCl3:Eu. Single crystals of CsCaI3:Eu and CsCaCl3:Eu were grown from the melt via the vertical Bridgman method. Scintillation properties, including decay time, light output, X-ray excited luminescence and light output, as a function of excitation energy were measured, as were the photoluminescence emission and excitation spectra. In addition, moisture sensitivity was evaluated by measuring the moisture uptake rate and compared with those of NaI:Tl and Cs2LiYCl6:Ce reference scintillators. [Copyright &y& Elsevier]

• Li+, Na+, and K+ codoped LuYAG: 1.2% Pr crystals were grown by Czochralski method. • Changing growth geometry, translation and rotation rate mitigates cracking in LuYAG. • Codoping with monovalent ions improves light yield, energy resolution, decay time. • Enhanced properties are associated with the removal of charge carrier trap at 300 K. In this paper, we explore codoping with monovalent ions: Li+, Na+, and K+, as a method of altering the scintillation properties of praseodymium-doped (Lu 0.75 Y 0.25) 3 Al 5 O 12 (LuYAG: Pr3+) single crystals. Substantial effort was given to optimizing the growth process to mitigate cracking which occurred in the LuYAG crystals beginning around the shoulder region and continuing throughout the boule. Growth parameters such as the translation and rotation rate, cool down duration, and boule geometry were altered to successfully address this challenge. Scintillation light yield, energy resolution, and scintillation decay time were measured for each of these crystals. It was discovered that monovalent codoping significantly improved scintillation light yield by at least 50%; accelerated and increased the weight of the fast component of scintillation decay; and enhanced energy resolution to values of as low as 3.8%, the best energy resolution reported for an oxide scintillator to date. The enhancements in scintillation performance are related to the effect of monovalent codoping on the formation of defects, in particular oxygen vacancies, within the LuYAG matrix and is proven via thermoluminescence and afterglow measurements. [ABSTRACT FROM AUTHOR]

• Mixed scintillator CeBr 3−x I x was investigated. • X-ray diffraction was used to determine the structure both phases that formed. • Five singled crystals were grown via the vertical Bridgman technique. • A light yield of >80,000 ph/MeV was measured for the grown crystal CeBr 2 I. CeBr 3 is an intrinsic scintillator that has promising performance capabilities such as 60,000 ph/MeV and ~4% energy resolution at 662 keV. It has been shown that halide mixing can improve the light yield of single halide scintillators. In this work we attempted to improve on CeBr 3 by creating a mixed halide composition CeBr 3−x I x. Analysis of melt-freeze samples revealed that the light yield of CeI 3 rapidly increases as bromine is substituted. Thirteen mm diameter crystals were grown using the vertical Bridgman technique, with x values between 0.03 and 1. The CeBr 2.5 I 0.5 crystal segregated into two sections, colorless and green, while the CeBr 2 I crystal was entirely green. X-ray diffraction analysis was used to identify the two phases. Decay time increased as iodine concentration increased. All colorless phase crystals reached <4.5% energy resolution at 662 keV and >65,000 ph/MeV, with the CeBr 2.94 I 0.06 crystal achieving 3.9% energy resolution at 662 keV. The green phase crystals both reached light yields of 78,000 ph/MeV, the highest ever recorded for a CeI 3 phase crystal. [ABSTRACT FROM AUTHOR]