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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]

Block detector designs, utilizing a pixelated scintillator array coupled to a photosensor array in a light-sharing design, are commonly used for positron emission tomography (PET) imaging applications. In practice, the spatial sampling of these designs is limited by the crystal pitch, which must be large enough for individual crystals to be resolved in the detector flood image. Replacing the conventional 2D scintillator array with an array of phoswich elements, each consisting of an optically coupled side-by-side scintillator pair, may improve spatial sampling in one direction of the array without requiring resolving smaller crystal elements. To test the feasibility of this design, a 4 × 4 phoswich array was constructed, with each phoswich element consisting of two optically coupled, 3 . 17 × 1 . 58 × 10 mm 3 LSO crystals co-doped with cerium and calcium. The amount of calcium doping was varied to create a ‘fast’ LSO crystal with decay time of 32.9 ns and a ‘slow’ LSO crystal with decay time of 41.2 ns. Using a Hamamatsu R8900U-00-C12 position-sensitive photomultiplier tube (PS-PMT) and a CAEN V1720 250 MS/s waveform digitizer, we were able to show effective discrimination of the fast and slow LSO crystals in the phoswich array. Although a side-by-side phoswich array is feasible, reflections at the crystal boundary due to a mismatch between the refractive index of the optical adhesive ( n = 1 . 5 ) and LSO ( n = 1 . 82 ) caused it to behave optically as an 8 × 4 array rather than a 4 × 4 array. Direct coupling of each phoswich element to individual photodetector elements may be necessary with the current phoswich array design. Alternatively, in order to implement this phoswich design with a conventional light sharing PET block detector, a high refractive index optical adhesive is necessary to closely match the refractive index of LSO. [ABSTRACT FROM AUTHOR]

Codoping is a method of current interest for modifying the properties of scintillators. The study reported here explores the effect of codoping on cerium doped Gd 3 Ga 3 Al 2 O 12 (GGAG:Ce) crystals with various concentrations of Ca. These single crystals were grown via the Czochralski technique with Ce concentrations fixed at 0.2 at% and Ca concentrations ranging from 0.1 at% to 0.4 at% in the initial melt. The relationship between dopant concentration and light yield, rise time, and scintillation and photoluminescence decay times was determined. In addition, the absorbance, photoluminescence, radioluminescence, afterglow and thermoluminescence dependence on the dopant concentration are presented. In some of the Ca codoped crystals, an additional luminescence center was observed with an excitation wavelength of 350 nm and an emission wavelength of 400 nm and a photoluminescence decay time of ~3.5 ns. [ABSTRACT FROM AUTHOR]

Polycrystalline Gd 3 Ga 3 Al 2 O 12 :Ce (GGAG:Ce) pellets with various codopants were prepared via solid-state synthesis and characterized by X-ray diffraction, radioluminescence (RL), photoluminescence (PL), reflectivity and PL decay measurements. GGAG:Ce pellets codoped with B and Ba were found to have higher RL intensity than pellets with other codopants, while Ca codoping improved the decay time but reduced the RL intensity. These results were strongly correlated with the performance of these codopants in GGAG:Ce single crystals. The light yield of the single crystals codoped with B or Ba was ∼15% higher than the light yield of the GGAG:Ce crystal without codoping, while Ca codoping in single crystals resulted in lower light yield but shorter scintillation decay time (43 ns vs. 56 ns). The consistent performance of these codopants in both matrix forms indicates that sintering pellets may be used as a simple cost effective technique to evaluate compositions for likely single crystal scintillator performance. [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]

Recently discovered scintillators Cs 4 SrI 6 :Eu and Cs 4 CaI 6 :Eu have shown promising properties for gamma-ray detection in homeland security applications, with <4% energy resolution (at 662 keV) and light yields above 50,000 ph/MeV. However, a thorough investigation of the effects of europium concentration has not yet been conducted. In this work, Eu2+ concentration was varied from 0.5 mol% to 9 mol%, and Ø7 mm single crystals were grown from the melt via the vertical Bridgman method. Scintillation performance was evaluated as a function of Eu2+ concentration to determine the optimal amount. The observed trend was improved energy resolution and higher light yield with increasing Eu2+ concentration up to 7 mol%. The best energy resolution achieved was 3.2% for Cs 4 SrI 6 :Eu 7% and 3.6% for Cs 4 CaI 6 :Eu 7%. Their respective light yields were 71,000 ph/MeV and 69,000 ph/MeV. • Photoluminescence and radioluminescence emission show weak dependence on europium concentration in Cs4SrI6:Eu and Cs4CaI6:Eu. • A maximum light yield of 78,000 ph/MeV is obtained with 9 mol% europium in Cs4SrI6:Eu. • An energy resolution of 3.2% at 662 keV is achieved with 7 mol% europium in Cs4SrI6:Eu. [ABSTRACT FROM AUTHOR]

Abstract Recent studies have shown that under certain environmental conditions, plastic scintillators which are used in a variety of applications in outdoor environments develop defects called "fogging", resulting in a reduced useful lifetime and increased maintenance cost. Applications of plastic scintillators include scanning recycled steel going into a processing plant, personnel portals to scan employees, and scanning cargo and cars crossing borders of many countries. In this report, fogging was studied in conventional PVT and PS-based plastic scintillators, both field aged and freshly cast. A new fogging-resistant PVT-based formulation developed by scientists at Lawrence Livermore National Laboratory (LLNL) was tested as well. We used accelerated aging experiments via temperature and humidity cycling in controlled laboratory conditions to create observable temporary fogging defects in small samples (≤ 1 in3). Photoluminescence and optical transmission studies were used to evaluate the effect of the fogging. The time evolution of the induced temporary fogging formation and defogging (i.e. fading of defects in ambient conditions over time) were recorded using optical microscopy, time-lapse photography, and gravimetric analysis. [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]

A self-activated Cs 4 YbI 6 single crystal was grown by the vertical Bridgman method. Crystal structure refinements verified the phase purity and the trigonal crystal system with a space group of R 3 ̅ c. By using differential scanning calorimetry, the melting and crystallization points were determined to be 550 and 510 °C, respectively. Luminescence and scintillation properties were systematically studied. Upon ultraviolet light (360 nm) excitation, the Cs 4 YbI 6 crystal exhibits bluish-green emission centered at 450 and 480 nm due to spin-allowed and spin-forbidden transitions of Yb 2+ activators. The lifetimes of the corresponding emission bands at room temperature are tens and hundreds of nanoseconds, respectively. X-ray excited radioluminescence spectrum is dominated by the spin-forbidden transition of Yb 2+ at 480 nm. The absolute light yield is 2700 ± 200 photons/MeV with a principal scintillation decay time of 33 ns. The physical explanation for the low light yield observed is proposed from experimental and theoretical insights. [ABSTRACT FROM AUTHOR]

KCaI 3 :Eu single crystals exhibit favorable scintillation properties and have potential for use in domestic security applications requiring radioisotope identification. The anisotropic thermal expansion of the orthorhombic unit cell of this perovskite-type scintillator has been investigated using in-situ high temperature X-ray diffraction on powdered samples. Samples from single crystals of both pure and Eu-doped KCaI 3 grown by the Bridgman method were used for comparison. Expansion with temperature along the b -axis is greatest with an average linear coefficient of thermal expansion of ≈ (41–46) x 10 −6  K −1 resulting from the weaker bonding between alternating layers of K and Ca parallel to the b -axis. Thermal expansion in each of the KCaI 3 samples has the highest degree of anisotropy with respect to the b and c axis with ratio ᾱ b /ᾱ c of 1.4–1.5. Additionally, we identify the predominant cleavage plane in KCaI 3 as (0 -3 -1) based upon Laue reflection imaging. [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]

Inch-sized scintillating crystals are required for practical radiation detectors such as hand-held radio-isotope identification devices. In this work, a transparent and colorless 2-inch diameter KCa 0 . 8 Sr 0 . 2 I 3 : 0 . 5 mo % E u 2 + single crystal was grown by the vertical Bridgman method, and the scintillation properties of a ∅ 50 mm × 45 mm long sample were evaluated. The Eu 2 + 5 d 1 - 4 f emission under X-ray excitation is centered at 472 nm. Its scintillation decay time under 137 Cs source irradiation is 2 . 37 μ s , and the absolute light output is 51,000 ± 3000 photons/MeV. The energy resolution at 662 keV was evaluated for different orientations of the crystals with respect to the PMT, and the effect of 40 K background subtraction on energy resolution was evaluated. The performance of the packaged crystal was also investigated. [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]

Due to their reported fast decay times, Cs 2 ZnCl 4 and Cs 3 ZnCl 5 are promising candidates for detection of gamma rays and X-rays in high count rate and fast timing applications. In this work, we show that single crystals with better optical quality than previously demonstrated – and larger in size – can be grown via the vertical Bridgman method. Highly transparent Ø7 mm crystals of undoped Cs 2 ZnCl 4 and Cs 3 ZnCl 5 are grown and measured to have light yields surpassing those previously reported, achieving 1980 ± 100 ph/MeV and 1460 ± 70 ph/MeV at 662 keV – a 55% and 232% improvement, respectively. We observe single-component scintillation decay times for both Cs 2 ZnCl 4 (1.66 ns) and Cs 3 ZnCl 5 (0.82 ns) and radioluminescence emission with maximum intensity at ∼290 nm. Scalability of these materials is also evaluated based on growth of Ø22 mm crystals. Minimal cracking is observed, and the fast decay times are maintained at this size. Coincidence time resolution of 3 × 3 × 5 mm3 and 7 × 7 × 10 mm3 pixels cut from Ø22 mm Cs 2 ZnCl 4 are measured to be 148 ± 1 ps FWHM and 175 ± 1 ps FWHM, respectively. The improved performance and ability to be fabricated in large sizes now place Cs 2 ZnCl 4 and Cs 3 ZnCl 5 on the map as potential contenders for radiation detection applications where BaF 2 – the most commonly used ultrafast inorganic scintillator – is typically considered. • Single crystals of Cs 2 ZnCl 4 and Cs 3 ZnCl 5 were grown by the vertical Bridgman method. • Cs 2 ZnCl 4 had a scintillation decay time of 1.66 ns and light yield of 1980 ph/MeV at 662 keV. • Cs 3 ZnCl 5 had a scintillation decay time of 0.82 ns and light yield of 1460 ph/MeV at 662 keV. • The coincidence time resolution of Cs 2 ZnCl 4 was measured to be as good as 136 ± 2 ps FWHM. [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]

We report here the effect of Eu 2+ concentration in KCa 0.8 Sr 0.2 I 3 :Eu 2+ single crystal scintillators. KCa 0.8 Sr 0.2 I 3 :Eu 2+ single crystals doped with 0.5, 1, 3, 5, and 7 mol% Eu 2+ were grown by the Bridgman method. The effects of varying Eu 2+ concentration and crystal volume on the scintillation properties, including light yield, energy resolution, nonproportionality, scintillation decay time and afterglow level, were systematically investigated. For 5 mm×5 mm×5 mm samples, the best light yield of 86,000±4000 photons/MeV was achieved with a content of 5 mol% Eu 2+ ; its energy resolution of 2.5% at 662 keV was comparable to that of LaBr 3 :Ce 3+ and SrI 2 :Eu 2+ . With larger samples of about 2.2 cm 3 , the best performances achieved were for 3 mol% Eu 2+ concentration, i.e. a light yield of 76,000±4000 photons/MeV and an energy resolution of 3% at 662 keV. A direct correlation between nonproportionality and Eu 2+ concentration was found. A continuous lengthening of scintillation decay time and x-ray induced afterglow level with increasing Eu 2+ concentration was observed. The self-absorption effect was evaluated by using the Stokes shift and the temperature dependence of the photoluminescence decay (PL) of the Eu 2+ centers. The sample with the highest dopant concentration had more severe temperature quenching of the Eu 2+ 5d-4f emission than the sample with the lowest dopant concentration, which could be ascribed to the thermally activated concentration quenching. [ABSTRACT FROM AUTHOR]

Multicomponent garnet materials can be made in optical ceramic as well as single crystal form due to their cubic crystal structure. In this work, high-quality Gd 3 Ga 3 Al 2 O 12 :0.2 at% Ce (GGAG:Ce) single crystal and (Gd,Lu) 3 Ga 3 Al 2 O 12 :1 at% Ce (GLuGAG:Ce) optical ceramics were fabricated by the Czochralski method and a combination of hot isostatic pressing (HIPing) and annealing treatment, respectively. Under optical and X-ray excitation, the GLuGAG:Ce optical ceramic exhibits a broad Ce 3+ transition emission centered at 550 nm, while the emission peak of the GGAG:Ce single crystal is centered at 540 nm. A self-absorption effect in GLuGAG:Ce optical ceramic results in this red-shift of the Ce 3+ emission peak compared to that in the GGAG:Ce single crystal. The light yield under 662 keV γ-ray excitation was 45,000±2500 photons/MeV and 48,200±2410 photons/MeV for the GGAG:Ce single crystal and GLuGAG:Ce optical ceramic, respectively. An energy resolution of 7.1% for 662 keV γ-rays was achieved in the GLuGAG:Ce optical ceramic with a Hamamatsu R6231 PMT, which is superior to the value of 7.6% for a GGAG:Ce single crystal. Scintillation decay time measurements under 137 Cs irradiation show two exponential decay components of 58 ns (47%) and 504 ns (53%) for the GGAG:Ce single crystal, and 84 ns (76%) and 148 ns (24%) for the GLuGAG:Ce optical ceramic. The afterglow level after X-ray cutoff in the GLuGAG:Ce optical ceramic is at least one order of magnitude lower than in the GGAG:Ce single crystal. [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]

In this paper we report on the scintillation properties of TlSr 2 I 5 doped with Eu2+, a novel thallium-containing high-resolution scintillator for gamma-ray spectroscopy. Small diameter, good quality crystals of TlSr 2 I 5 :Eu (TSI) with different Eu2+ concentrations were grown by the vertical Bridgman method. X-ray diffraction measurements show that single crystals of TSI belong to the monoclinic system with space group P2 1 /c. TlSr 2 I 5 has a density of 5.32 g/cm3 and effective Z of 60. The X-ray excited emission of Eu2+ doped TlSr 2 I 5 features a broad emission band peaking between 460–470 nm. The light yield of TlSr 2 I 5 crystal doped with 1% Eu2+ is measured to be ∼ 72,000 ph/MeV with an energy resolution of 2.8% at 662 keV. The scintillation decay time which is characteristic of Eu2+ shows two components, with ∼ 90% of the light in a ∼ 500 ns component and the rest in a longer component of ∼ 3 μ s. [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]

In this paper we report on the crystallographic and scintillation properties of Tl 2 LaCl 5 :Ce 3 + and Tl 2 LaBr 5 :Ce 3 + , two novel thallium-containing high-resolution scintillators for gamma-ray spectroscopy. Crystals of Tl 2 LaCl 5 :Ce 3 + and Tl 2 LaBr 5 :Ce 3 + were grown by the Vertical Bridgman method up to 1-inch diameter and 1-inch long. Single crystals of Tl 2 LaCl 5 :Ce 3 + and Tl 2 LaBr 5 :Ce 3 + belong to the orthorhombic system with space group 62 and have a density of 5.16 and 5.98 g/cm3, respectively. The scintillators show high light yields of up to 68,000 photons/MeV, excellent gamma-ray energy resolution of ≤ 3% at 662 keV, a fast scintillation decay, and a proportional response over a wide range of energies from 32 keV up to 1275 keV. Density Functional Theory calculations show that the Ce 3 + energy levels are inside the bandgap despite the smaller bandgap of Tl 2 LaCl 5 and Tl 2 LaBr 5 compared to K 2 LaCl 5 and K 2 LaBr 5. A systematic Ce 3 + concentration study was performed for Tl 2 LaCl 5 :Ce 3 + and trends observed. [ABSTRACT FROM AUTHOR]

Europium doped strontium iodide (SrI 2 :Eu 2 +) is one of the cutting-edge halide scintillators for gamma-ray spectroscopy applications due to its low radioactive background, ultrahigh light yield (70,000–100,000 photons/MeV), and excellent gamma-ray energy resolution (2.6%–3% at 662 keV). In this work, we report an improvement in the scintillation characteristics of SrI 2 :Eu 2 + single crystals via tetravalent ion codoping, namely Zr 4 +. High quality SrI 2 :Eu 2 + single crystals codoped with 0, 0.05, 0.1, and 0.2 at.% Zr 4 + were grown by the Multi-ampoule Bridgman method. All of the as-grown crystals are transparent, crack-and inclusion-free. They have high optical quality with a transmittance of over 70%. The effects of Zr 4 + codoping on spectral properties and decay kinetics of SrI 2 :Eu 2 + under optical, and x- and gamma-ray excitation are studied. An enhancement of gamma-ray spectroscopic resolution from 2.8 to 2.5% at 662 keV and 5.4 to 5% at 122 keV is achieved upon Zr 4 + codoping with a slightly enhanced light yield of 95,000 photons/MeV. [ABSTRACT FROM AUTHOR]

• 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]

Fogging in plastic scintillators is a degradation mechanism that reduces light collection efficiency. In an effort to reduce maintenance costs, multiple groups have attempted to understand and prevent this problem by changing plastic compositions and system level designs. New formulations have been produced that are promising with respect to fogging resistance. In this current work we study a variety of new compositions by subjecting them to an accelerated aging experiment with varying temperature and humidity profiles. Compositions are analyzed for their resistance to degradation after saturation periods, with those containing polymethyl methacrylate and divinyl benzene being the most promising. Pulse height spectra revealed that after environmental aging, many of the samples suffered a reduction in light yield to different degrees, even those that did not fog. This result could be due to heating of the samples and may be prevented by further production optimization. [ABSTRACT FROM AUTHOR]

In this paper, we present the photoluminescence and scintillation performance of Pr3+ doped (Lu 0.75 Y 0.25) 3 Al 5 O 12 single crystals as a function of Li+ concentration. Lithium concentration had no effect on the optical properties of LuYAG: Pr single crystal scintillators regardless of concentration. On the other hand, scintillation light yield increased by as much as 94% with the incorporation of lithium as a codopant, and the energy resolution at 662 keV was improved to 4.1%, which is an outstanding energy resolution for an oxide single crystal scintillator. Lithium codoping slightly lengthened the fast component of the scintillation decay time, and slightly decreased the contribution from the slow component. Additionally, the samples were annealed in air and scintillation properties were compared before and after this annealing treatment. The change in scintillation properties is explained through the analysis of thermoluminescence glow curves. • Li codoping of LuYAG: Pr can increase light yield, improve energy resolution. • Air annealing improves light yield of LuYAG: Pr, Li by reducing trap concentration. • Thermoluminescence suggests traps play important role in scintillation mechanism. [ABSTRACT FROM AUTHOR]