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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]

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]

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]

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]

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]

In this paper, nine different samples of \ YAIO3:{\ {Ce}} have been collected and analyzed. The light yield non-proportionality of each sample was measured and used to classify each sample as proportional or non-proportional. A variety of scintillation and optical measurements were conducted on each sample, and the proportional samples were generally found to have a higher light output and better energy resolution. In addition, a strong linear correlation was found between scintillation decay time and the degree of non-proportionality. Based on absorption measurements as well as radioluminescence data, it was determined that the non-proportional samples all shared a range of increased absorption near the cerium 5d absorption edge between about 325 and 400 nm. The increased absorption has been reported in literature, and it is believed to be the result of a material defect introduced during growth. Thermoluminescence glow curves were measured for two representative \ YAIO3:{\ {Ce}} samples, one from each proportionality grouping, and it was determined that there was an observable change in defect structure, but there were no additional traps visible in the glow curves of either the proportional or non-proportional samples. However, the intensity of the 105 K thermoluminescence peak was found to be approximately a factor of two greater in the non-proportional samples. Since the lifetime of this peak is known to be between 25 and 81 ns, it was determined to be the likely cause of the slower decay in the non-proportional samples. [ABSTRACT FROM PUBLISHER]

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]