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Time‐resolved spectroscopic study of the photoluminescence response to femtosecond pulse excitation and free carrier absorption at different wavelengths, thermally stimulated luminescence measurements and investigation of differential absorption are applied to amend the available data on excitation transfer in GAGG:Ce scintillators, and an electronic energy‐level diagram in this single crystal is suggested to explain the influence of codoping with divalent Mg on luminescence kinetics and light yield. The conclusions are generalized by comparison of the influence of aliovalent doping in garnets (GAGG:Ce) and oxyorthosilicates (LSO:Ce and YSO:Ce). In both cases, the codoping facilitates the energy transfer to radiative Ce3+ centers, while the light yield is increased in the LYSO:Ce system but reduced in GAGG:Ce. [ABSTRACT FROM AUTHOR]

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]

Single crystals of Gd3Ga3Al2O12 : Ce with different codopants were successfully grown using the Czochralski technique. Optical and scintillation properties of these codoped crystals were studied in detail including absorption, photoluminescence excitation and emission, decay time and thermoluminescence. This study revealed that while boron codoping improves the scintillation light output and energy resolution and decreases self-absorption in these crystals, calcium codoping affects their properties in the opposite manner. In addition to antisite defects, the effect of room temperature trap centres on the sensitivity of these crystals to light exposure is also reported for the first time. Light sensitivity was also found to be affected with the incorporation of codopants in the lattice. The effect of annealing in oxidizing and reducing atmospheres on the scintillation and optical properties of differently codoped crystals was also investigated in detail in order to better understand the defect structure of these crystals. All these measurements together are used to explain the effect of codoping on the crystal field and defect structure of these crystals. [ABSTRACT FROM AUTHOR]

The temperature dependence of the photoluminescence properties of Gd2SiO5:Ce,Ca crystals was found to be significantly affected by Ca codoping and shows that presence of additional energy levels in these crystals provides nonradiative energy transfer. The excitation and emission bands also broaden with codoping due to presence of these additional energy levels. Therefore Ca codoping in Gd2SiO5 crystals decreases the scintillation decay very strongly and has a strong adverse affect on scintillation light yield, different from the effect in other members of the oxyorthosilicate family such as Lu2SiO5 and Y2SiO5. [ABSTRACT FROM PUBLISHER]

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]

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]

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]

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]