Search

Electron traps are known to a have great influence on the carriers transport process in Ce based scintillators. On the other hand, the role of hole traps in the scintillation process has been less considered. By means of electron spin resonance (ESR), we detected hole traps in highly Ce-doped LuAG:Ce,Mg ceramics in the form of σ-type O- centers. The g -tensor components turn out to be g⊥ = 2.0103, and g|| = 2.0023, revealing the axial symmetry of these defects. Mg-perturbed variants of O- centers are proposed to exist in LuAG:Ce,Mg. Their occurrence is related to an elongated Mg-O bond as evidenced by DFT calculations. Finally, the multiple role of O- centers in the scintillation process is discussed. [ABSTRACT FROM AUTHOR]

We used combustion synthesis to produce phase pure GdOBr:Ce with varying Ce concentration. Several combinations of NH4Br and fuel concentration were tested before phase pure GdOBr:Ce was produced by using a 50% excess of NH4Br and a 50% lean concentration of fuel. In addition to the expected emissions from Ce and Gd, we also detected emissions from Eu3+ and Tb3+. Further research indicated that these extra rare earth emissions were due to impurities in the Gd2O3 starting material. While not the desired effect, we were able to monitor both Eu and Ce intensities as a function of Ce concentration in GdOBr. The Ce emission is seen to reach a maximum between 0.1 and 0.5 mol%. At higher Ce content, the Ce luminescence is quenched because of the concentration quenching effect and the higher concentration of O-H and N-H groups as revealed by IR spectra. Eu emission progressively decreases as Ce content increases from a combination of competition with Ce for charge capture in the RL process and the effect of OH and NH groups. As Ce concentration increases the RL intensity ratio of the bands of the Ce doublet changes even though the energy difference between the two bands (0.24 ± 0.1 eV) is compatible with the spin-orbit splitting of the ground level of Ce3+ (0.25 eV). Fitting results indicate that this relative change is not due to changes in self-absorption, and the effect may be due to changes in local symmetry of the Ce ion. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We bring into consideration a novel, potentially promising scintillating material, Pb-doped SrHfO3. The structural and optical properties of a series of Pb-doped SrHfO3 powders prepared by acetate and citrate combustion are investigated and compared to those of undoped and Ce-doped powders with the same composition. Room temperature radioluminescence studies as a function of sintering temperature show that samples sintered up to the highest final temperature (1150 °C) display the highest light output. Moreover, Pb-doped SrHfO3 shows a higher radioluminescence efficiency with respect to Ce-doped SrHfO3, which in turn features a very fast photoluminescence decay time of 15 ns. The presence of point defects and their role in carrier trapping are studied by thermally stimulated luminescence as well as by radioluminescence as a function of temperature. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the influence of shallow traps on scintillating properties of YAlO3 : Ce. Wave- length-resolved thermally stimulated luminescence measurements following X-ray irradiation at 10 K have been performed on both undoped and Ce-doped crystals. Different and composite glow curves and emission spectra were obtained. Following glow peaks analysis of YAlO3 : Ce, their room temperature decay time was evaluated to be of the order of 10-4 s. The presence of an athermal tunneling recombination process between traps and Ce3+ ions below 100 K has been evidenced by phosphorescence decays. [ABSTRACT FROM AUTHOR]

The recent trends in scintillator technologies stimulate research efforts toward the development of novel materials morphologies, such as nanoparticles, able to efficiently convert ionizing radiations into light. For example, scintillating nanoparticles attract great interest in medical oncological therapies. In this work, the structural and morphological properties of HfO2:Ti nanoparticles with Ti concentrations from 0.03 to 10 mol% and subjected to calcination up to 1000 °C are thoroughly characterized; moreover, X‐ray photoelectron spectroscopy reveals the incorporation of Ti in both Ti (III) and Ti (IV) chemical states in as prepared samples, while the exclusive presence of Ti(IV) is unambiguously identified in calcined nanoparticles. The optical emission under X‐ray excitation evidences an intense Ti (IV)‐related luminescence at 2.5 eV in high temperature calcined samples with a few microseconds scintillation lifetime, and efficiency comparable to that of Bi4Ge3O12 reference scintillator. Finally, the competitive role of defects in charge carriers capture is demonstrated by the monotonic increase of the 2.5 eV band during prolonged X‐ray irradiation, more evident for nanoparticles with titanium concentration below 1 mol%. HfO2:Ti may also find application in X‐ray triggered oncological therapies by using the Ti (IV)‐related bright radioluminescence to excite photosensitizer molecules for singlet oxygen generation. [ABSTRACT FROM AUTHOR]

Lutetium aluminum garnet, commonly known as LuAG, is a versatile material finding numerous optical applications, and whose scintillation properties have been widely investigated. In this study, experimental evidences of optically stimulated luminescence (OSL) phenomena occurring in LuAG:Ce crystals are shown. After demonstrating the possibility to optically bleach an electron trap responsible for a thermally stimulated luminescence (TSL) peak at 280 °C (heating rate 1.7 °C s−1) using red light, a direct measurement of the OSL decay curve and of the resulting characteristic Ce3+ 5d‐4f emission spectrum is carried out. The assessment of the bleaching spectrum of the TSL peak at 280 °C reveals that light with wavelength in the 600–650 nm interval is the most efficient in depleting the TSL peak, making He‐Ne lasers suitable sources of optical stimulation. The finding of OSL features in LuAG:Ce paves the way to new application perspectives. In particular, the achievement of a good balance between scintillation and energy storage properties of LuAG.Ce can drive a constructive integration between X‐rays imaging approaches based on photo‐stimulable phosphors and those exploiting scintillating materials. [ABSTRACT FROM AUTHOR]

Optical absorption, luminescence, and scintillation characteristics of Lu3Al5O12:Ce optical ceramics were measured and compared with an analogous high quality single crystal. Optical absorption of the former shows an additional light scattering loss due to nanovoids and/or refraction index inhomogeneities. Even though radioluminescence intensity of the optical ceramics prepared by a coprecipitation route exceeds that of single crystal, its scintillation light yield is lower due to the charge carrier retrapping in the process of energy transfer towards the Ce3+ emission centers. Retrapping processes are evidenced by thermoluminescence measurements below room temperature. Lu3Al5O12:Ce optical ceramics does not show the presence of the LuAl antisite defects which decreases the scintillation figure of merit in single crystals grown from the melt [M. Nikl, Phys. Status Solidi A 202, 201 (2005)]. Furthermore, using the ceramic technology, one can achieve both the homogeneous doping and higher Ce concentration. Similar to Y3Al5O12:Ce, the optical ceramics may therefore become competitive to the Lu3Al5O12:Ce single crystals, if trapping phenomena at other defects can be further reduced. [ABSTRACT FROM AUTHOR]

Optical properties of yttria-aluminoborate (YAB) glasses with general composition 10(Ce x Tb y Y (1-x-y) )-30Al 2 O 3 -60B 2 O 3 are investigated and compared with data available on YAB crystals with huntite-like structure. Ce doped samples show optical features ascribable to preferential location of rare earth ions in sites with specific geometry similar to that observed in crystalline structures. Samples prepared with Tb ions as emission activator and Ce ions as sensitizer have been studied within the framework of non-radiative energy transfer. The resulting Förster radius is of 4.6 ± 0.5 Å comparable with that observed in Ce/Tb co-doped YAl 3 (BO 3 ) 4 crystals. The investigated materials possess radio- and photoluminescence emission efficiencies and performances comparable to that of crystalline counterparts with the advantage of having easiness of preparation and workability typical of glassy systems. [ABSTRACT FROM AUTHOR]

Knowledge of the kinetic parameters E (thermal activation energy) and s (frequency factor) of charge-trapping defects in the quartz crystal lattice is of paramount importance to assessing the thermal stability of associated luminescence signals used for dosimetry and dating. Since methods proposed for constraining thermoluminescence (TL) kinetics usually make use of the signal response to thermal treatments, accurate temperature control is required to obtain valid E and s values. In an attempt to check the extent to which consistent kinetic parameters could be obtained using routine luminescence measurement equipment, we have investigated three methods (isothermal decay, initial rise and the Hoogenstraaten method) in an inter-comparison study involving eight laboratories using Risø and Freiberg Instruments systems. The target signal was the so-called 110 °C TL peak of a sample of Oligocene coastal dune quartz sand from the Fontainebleau sand formation (France). TL glow curves recorded with heating rates in the range 0.02–5 K s −1 showed peak positions varying up to 60 °C between systems at the highest heating rates, attributed to temperature calibration errors and/or thermal lag. Kinetic parameters derived from the complete data set show a large spread, covering the ranges ∼0.5–1.2 eV and 10 6 –10 17 s −1 for E and s . In most cases, interlaboratory variations exceeded those of replicate measurements within individual laboratories. Signal lifetimes at 20 °C derived from the isothermal decay (∼59 min) and initial rise methods (at low heating rates; ∼60–80 min) most closely match the value directly measured at 20 °C from within two luminescence readers (∼70 min). Finally, we discuss the consequences of these findings for dosimetry and dating using luminescence signals and possible ways to reduce systematic errors in laboratory measurements of kinetic parameters. [ABSTRACT FROM AUTHOR]

Abstract: Structural and optical properties of sol–gel silica based glassceramics doped with 0.1mol% Ce and codoped with Gd at high concentrations, from 5mol% up to 40mol%, are investigated and compared to those of analogous samples doped only with Ce. Raman scattering, transmission electron microscopy, and x-ray diffraction reveal the formation of Gd apatite-like silicate (Gd4.67O(SiO4)3) and of Gd pyrosilicate (Gd2Si2O7) nanophases whose morphology and crystallinity depend on the Gd concentration and thermal treatments. Optical absorption measurements demonstrate the role of the densification atmosphere in modifying the charge state of Ce ions. The incorporation of Ce3+ ions in the nanophases is put in evidence by photo- and radio-luminescence results. [Copyright &y& Elsevier]