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The effects of composition on the phase formation of multicomponent garnet crystals grown via directional solidification by the micro-pulling-down method are studied. A relatively wide range of rare-earth (RE) average ionic radii (AIR) is explored by formulating ten compositions from the system (Lu,Y,Ho,Dy,Tb,Gd)3Al5O12. Crystals were grown at either 0.05 or 0.20 mm min-1. The hypothesis is that multicomponent compounds with large AIR will form secondary phases as the single-RE aluminum garnets formed by larger Tb3+ or Gd3+; this will result in crystals of poor optical quality. Crystals with large AIR have a central opaque region in optical microscopy images, which is responsible for their reduced transparency compared to crystals with small AIR. Slow pulling rates suppress the formation of the opaque region in crystals with intermediate AIR. Powder and single-crystal X-ray diffraction and electron probe microanalysis results indicate that the opaque region is a perovskite phase. Scanning electron microscopy and energy dispersive spectroscopy measurements reveal eutectic inclusions at the outer surface of the crystals. The concentration of the eutectic inclusions increases with increasing AIR. [ABSTRACT FROM AUTHOR]

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]

Low temperature (∼35 K) measurements of the scintillation kinetics of Y2SiO5 : Ce (YSO:Ce) have previously illustrated that shallow electron traps can play an important role in the scintillation mechanism. In addition, divalent calcium co-doping of isostructural Lu2SiO5 : Ce (LSO:Ce) has been shown to eliminate shallow electron traps and decrease scintillation decay time while maintaining high light output. Here we investigate the effect of Ca2+ codoping on the trap populations and scintillation kinetics of YSO:Ce. Single crystals were grown with Ca2+ concentrations up to 0.5 at% relative to Y. Thermoluminescence measurements indicate a significant reduction in shallow traps, and a marked change in the scintillation kinetics can be seen in the scintillation time profiles as a result of Ca2+ codoping. [ABSTRACT FROM AUTHOR]

Commercially available Lu2SiO5:Ce (LSO:Ce) scintillators for the nuclear medical imaging applications, such as positron electron tomography (PET), normally have a light yield of 30 000–32 000 photons/MeV and a scintillation decay time of 43–45 ns. We demonstrate a simultaneous improvement of light yield and decay time of LSO:Ce single crystal scintillators with lithium codoping. Li codoping significantly enhances the light yield of LSO:Ce from 32 500 to 39 000 photons/MeV, shortens the scintillation decay time from 45.4 to 42.1 ns, and reduces the room temperature afterglow by around one order of magnitude. The physical insights on the role of Li codopants in scintillation mechanism are provided by studying cerium oxidation state, luminescence properties of cerium activator centers, defect structure, and preferential occupation of lithium ions. The improved light yield and afterglow are explained in terms of the dissociation of spatially correlated oxygen vacancies (VO) and Ce centers or the suppression of VO formation, allowing a more efficient electron migration to Ce centers. We attribute the decay time shortening upon Li+ codoping to the reduction of slow Ce2 emissions via a non‐radiative energy transfer from six‐coordinated Ce2 to seven‐coordinated Ce1 centers. This letter reports a simultaneous improvement of light yield, decay time, and afterglow of Lu2SiO5:Ce3+ scintillation detectors by Li+ codoping. Analysis reveals the non‐conversion of stable Ce3+ to Ce4+ upon Li codoping, and the critical role of Li site occupancy on the suppression of oxygen vacancies. This strategy is also expected to be extended to other oxide scintillators. [ABSTRACT FROM AUTHOR]

In this work the Bridgman crystal growth and scintillation properties of both undoped and Tl-doped Cs 3 Cu 2 I 5 are presented. This material is very attractive for gamma and X-ray detection applications, with a density of 4.53 g/cm3 and effective atomic number of 51.9. Undoped Cs 3 Cu 2 I 5 had a light yield of 41,500 photons/MeV, with an energy resolution of 4.4% at 662 keV. Thallium doping at 0.5 mol % resulted in a much-improved scintillation response, in which light yield increased to 98,200 photons/MeV and energy resolution reduced to 3.3% at 662 keV. The X-ray excited emission is centered at 442 nm for the undoped and 500 nm for the Tl-doped crystals. The undoped emission is broad, typical of excitonic emission, while thallium doping results in an even broader band with features of both the undoped and thallium defect-mediated emissions. • Transparent single crystals of undoped Cs 3 Cu 2 I 5 and Cs 3 Cu 2 I 5 (Tl) were grown via the Bridgman technique. • Phase purity was established via powder XRD analysis. • Undoped Cs 3 Cu 2 I 5 has 41,500 photons/MeV and 4.4% energy resolution at 662 keV. • Tl doping at 0.5 mol% improves light yield to 98,200 photons/MeV and energy resolution to 3.3%. [ABSTRACT FROM AUTHOR]

Abstract KCaI 3 :Eu is a scintillator composition that is promising for national security applications, with a high light yield and good energy resolution (∼ 70,000 ph/MeV and ∼ 3% E.R. at 662 keV, respectively). In addition to its high performance, we have been successful at growing KCaI 3 :Eu at larger sizes (38 mm diameter) without cracking. In this work we utilized a multi ampoule growth station to grow four 38 mm diameter crystals simultaneously. Three of these crystals achieved an energy resolution of ∼ 4% at 662 keV. The three crystals were hermetically packaged and a collimation study was carried out. This study revealed that light yield at a given irradiation location is dominated by photon path lengths and self-absorption, while the energy resolution dependence is affected heavily by local crystal quality. A 50 mm diameter KCaI 3 :Eu crystal was grown that achieved an energy resolution of 4.6% at 662 keV. GEANT4 was used to model a gap-style package that results in reduced photon path lengths, and therefore reduced self-absorption probability. [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]

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, ampule surface treatments, and temperature gradients. It was found that crystal cracking can be effectively prevented by using a carbon-coated quartz ampule 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 Φ22 mm x 22 mm and Φ38 mm x 35 mm samples were also investigated. [ABSTRACT FROM AUTHOR]

The rising demand for efficient radiation detectors in various applications has led to intense research on single crystal scintillators. The scintillation performance strongly depends on the as-grown crystal quality. Mixed-anion elpasolite single crystals with Ce-doping such as Cs2NaREBr3I3 (RE = La, Y) are among the most promising candidates as next generation scintillators. However, there are multiple challenges to traditional single crystal synthesis using melt-freeze growth techniques due to the complicated composition, as well as impurities, and varying thermal behavior of the starting materials. To improve the as-grown single crystal quality and optimize their scintillation properties, a series of investigations on material treatment and synthesis, ampule design, and crystal growth parameters were conducted. Effective purification of the carbon- and oxygen-based impurities improved the optical transmittance of the crystal. Differential scanning calorimetry and thermal gravimetric analysis results revealed the thermal instability of the compounds upon heating above the melting temperature. Multiple cycles of heating-soaking-cooling synthesis were applied, which significantly increased the completeness of chemical reactions. Improvements of the scintillation light yield and energy resolution of Ce-doped Cs2NaLaBr3I3 and Cs2NaYBr3I3 were achieved. Our results led to a better understanding of the crystal growth of mixed-anion elpasolites, as well as the optimization of techniques to engineer metal halide crystals in the future. [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]

In this paper we report on the crystal growth, density functional theory (DFT) calculations and scintillation properties of Tl 3 LnCl 6 :Ce 3 + and TlLn 2 Cl 7 :Ce 3 + (Ln = Y, Gd). Crystals were grown by the Vertical Bridgman technique up to 16 mm in diameter and 25 mm long. Crystals of Tl 3 YCl 6 :Ce 3 + and Tl 3 GdCl 6 :Ce 3 + belong to the family of the Nesohalides which have the monoclinic crystal structure. Crystals of TlY 2 Cl 7 :Ce 3 + and TlGd 2 Cl 7 :Ce 3 + belong to the family of the Phyllohalides which have either the monoclinic or the orthorhombic crystal structure. The light yields of these Nesohalides and Phyllohalides are typically on the order of 35,000–40,000 ph/MeV. [ABSTRACT FROM AUTHOR]

Yb2+ was investigated as a potential alternative activator for Cs 4 SrI 6 and Cs 4 CaI 6 scintillators for the first time, as opposed to the previously studied Eu2+ activator. Single crystals with nominal Yb2+ concentrations of 0.5 mol%, 1 mol%, and 3 mol% were grown in Ø7 mm ampoules using the vertical Bridgman method. Luminescence and scintillation properties were evaluated as a function of Yb2+ concentration and host compound. The 5 d → 4 f electronic transition of Yb2+ was observed for both the Sr- and Ca-containing compositions. X-ray induced radioluminescence emission was centered between 449 nm and 463 nm depending on Yb2+ concentration and host compound. Both the spin-allowed and spin-forbidden transitions were observed in photoluminescence emission spectra and were centered at 446 nm and 476 nm, respectively, for both compounds. The best scintillation performance was achieved with Cs 4 CaI 6 :Yb 1 mol%, which had a 3.5% energy resolution at 662 keV and 43,000 ph/MeV light yield. To our knowledge this is the best energy resolution ever reported for a Yb2+-doped scintillator. Additional Cs 4 CaI 6 :Yb 1% crystals were grown in Ø12 mm ampoules to investigate the size dependence of scintillation properties, as well as crystal homogeneity. • Single crystals of Cs4CaI6:Yb and Cs4SrI6:Yb were grown using the vertical Bridgman technique. • Cs4CaI6:Yb 1% has an energy resolution of 3.5% at 662 keV and light yield of 43,000 ph/MeV. • Emission from the Yb2+ spin-allowed and spin-forbidden transitions are both observed in photoluminescence spectra.. [ABSTRACT FROM AUTHOR]