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Cerium-doped YAlO3:Ce (YAP:Ce) is an interesting oxide scintillator that exhibits a wider range of light yield nonproportionality on a sample-to-sample basis than most other well-known oxide scintillators. In general, most oxide materials, such as Bi4Ge3O12 and Lu2SiO5:Ce, are thought to have an intrinsic proportional response that is nearly constant between samples and independent of growth conditions. Since light yield nonproportionality is responsible for degrading the achievable energy resolution of all known scintillators, it is important to understand what contributes to the behavior. In an attempt to understand if the phenomenon can be affected by growth parameters or by other means, seven samples of YAP:Ce were collected from various sources, and eight samples were grown in-house using the Czochralski method. Based on optical and scintillation measurement as well as direct measurement of the cerium concentration, it was determined that the light yield proportionality in YAP:Ce is strongly related to the cerium concentration. Samples that were found to have higher relative cerium concentration displayed a more proportional light yield response. In addition, it was determined that samples with higher cerium concentration also exhibit a faster decay time and an enhanced energy resolution when compared to samples with less cerium. It was also determined that growth in a reducing atmosphere can effectively suppress a parasitic optical absorption band. [ABSTRACT FROM PUBLISHER]

GGAG:Ce crystals with various Ca concentrations were grown by the Czochralski technique. The introduction of Ca2+ ions into a trivalent site results in a change in the Ce valence state as well as an additional F+ luminescence center. The changes of Ce valence state could be affected by various annealing atmospheres and were investigated via measuring the Ce3+ absorbance and observing the color change of the sample. Photoluminescence spectra and photoluminescence decay were used to reveal the occurrence of F+ center related to the oxygen vacancies during the annealing. A redox mechanism and a charge compensation process are proposed to explain the change in Ce state charge and F+ center during the annealing. [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]

Experimental studies of LSO:Ce crystals co-doped with various concentrations of Ca are presented. Photoluminescence decay time, excitation and emission spectra, thermal response and X-ray excited luminescence are investigated as a function of Ca concentration. Experimental data show Ca co-doping does not alter the energy level structure of either Ce1 or Ce2, but reduces the relative population of Ce2 to Ce1. Thus, the luminescence from Ce2 is suppressed, which contributes to the fast scintillation decay of Ca co-doped LSO:Ce. [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]

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 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]

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]

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]

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]