Coincidence time resolution (CTR) of scintillation detectors based on Ce- and Mg-codoped Gd 3 Al 2 Ga 3 O 12 (GAGG) scintillation crystals and high-density silicon photomultipliers (SiPMs) is shown ...to be 165 ps (full width at half maximum) for 511-keV <inline-formula> <tex-math notation="LaTeX">\gamma </tex-math></inline-formula>-quanta, approaching that achieved by using LSO scintillators. To study the prospective for further improvement of the time resolution, the population of the emitting Ce centers was investigated by optical pump and probe technique using selective photoexcitation and probing by a white light continuum with subpicosecond time resolution. The importance of free electron trapping for excitation transfer to emitting Ce ions was revealed. The influence of transfer delay on the scintillation response time is described, and the dynamics of electron relaxation to the lowest excited level of Ce ion is studied experimentally and analyzed by taking into account intracenter relaxation and relaxation via conduction band. The influence of electron diffusivity on the rise time of the population of the emitting level is described. It is shown that codoping of GAGG:Ce by magnesium even at the level as low as 10 ppm efficiently decreases the scintillator response time by enhancing the electron diffusivity.
A new inorganic scintillation material based on Ba-Gd silica glass doped with cerium (BGS) is fabricated and studied. With the highest light yield among heavy glasses at the level of 2500 ph/MeV and ...fast scintillation response, the new scintillator ensures a good coincidence time resolution of < 230 ps FWHM for 511 keV γ-quanta from a 22Na source and SiPM readout. In addition to good performance in γ-quanta detection, the material demonstrates capability for efficient detection of low-energetic neutrons. The scintillator is produced by exploiting the standard industrial glass technology, which allows for an unlimited scaling up the conversion of raw material into a high-quality scintillator at a high rate. The glass can be casted in application-specific molds, so minimizing the material losses. The presented glass scintillator has potential for further improvement of its light output and scintillation response time.
Non-linear absorption spectroscopy in pump and probe configuration has been used to test the population of non-equilibrium carriers in Ce-doped Y3Al5O12 (YAG), Lu3Al5O12 (LuAG), and Gd3AlxGa(5-x)O12 ...(GAGG) crystals with and without codoping by Mg2+ ions. A faster rise time of the induced optical density has been observed in all crystals codoped with Mg with respect to that in Mg-free samples. A significant difference in the time evolution of the differential optical density in GAGG with respect to YAG and LuAG crystals has also been measured. In both GAGG:Ce and GAGG:Ce,Mg an absorption band with maximum in the blue-green range and a decay time of 1.4ps is present. This band is due to the absorption by free electrons before they are trapped or re-captured by Ce3+ ions. A broad absorption band in the yellow-red region with very short rise time and a decay time longer than 150ps has been observed in all the Ce-doped garnets under study and can be attributed to the absorption from the Ce3+ excited states.
This report presents results on the significant improvement of GAGG:Ce based scintillation detector performance with temperature decrease. When temperature of a PMT based detector is lowered to ...−45 °C, its amplitude response at registration of γ-quanta is improved by 30%; FHHM was found to be better up to factor of 0.85, whereas scintillation kinetics become even faster in crystals co-doped with magnesium and magnesium and titanium. All this opens an opportunity for a wide application of GAGG scintillation detectors, particularly in a combination with SiPM photo-sensors, which signal-to-noise ratio would also improve with temperature decrease.
The time resolution of the detectors currently in use is limited by 50-70 ps due to the spontaneous processes involved in the development of the response signal, which forms after the relaxation of ...carriers generated during the interaction. In this study, we investigate the feasibility of exploiting sub-picosecond phenomena occurring after the interaction of scintillator material with ionizing radiation by probing the material with ultra-short laser pulses. One of the phenomena is the elastic polarization due to the local lattice distortion caused by the displacement of electrons and holes generated by ionization. The key feature of the elastic polarization is its short response time, which makes it prospective for using as an optically detectable time mark. The nonlinear optical absorption of femtosecond light pulses of appropriate wavelength is demonstrated to be a prospective tool to form the mark. This study was aimed at searching for inorganic crystalline media combining scintillation properties and non-linear absorption of ultra-short laser pulses. The nonlinear pump-and-probe optical absorption technique with 200 fs laser pulses was used to study the effects in lead tungstate, garnet-type, and diamond scintillator crystals.
Cerium-doped mixed garnet-type single crystals (GdxY1-x)3Al2Ga3O12 with different yttrium content have been fabricated and studied as a prospective scintillating material enabling improvement of ...scintillation properties by tuning the composition of the matrix-building crystal. The influence of the matrix composition on the emitting Ce ion is studied using linear and time-resolved nonlinear optical absorption and time-resolved photoluminescence spectroscopy. The study of photoluminescence at resonant excitation revealed a composite origin of Ce3+ emission band. This behavior is interpreted by the contribution of Ce3+ ions located in inequivalent positions expected due to the disorder caused in the garnet-type lattice of a mixed crystal by compositional fluctuations. The substitution of gadolinium by yttrium in the lattice results not only in an emission blue shift and in decreased splitting of the lowest doublet 5d state of Ce3+ but also in an increased separation between the lowest doublet level 5d1 and the lowest triplet 5d3 level, as well as in changing the rates of intracenter and extracenter energy relaxation.
Display omitted
•Photoluminescence spectrum is composite due to inequivalent positions of Ce3+ ions.•Decay time of Ce3+ emission decreases from 55 ns at 1.9 eV to 40 ns at 2.5 eV.•Substitution of Gd by Y decreases 5d1-5d2 splitting of Ce3+ and increases 5d1-5d3 separation.•Introduction of Y in GAGG lattice increases Ce3+ intracenter relaxation time.•Capture of trapped electrons to nonradiative recombination centers is enhanced in GYAGG.
ввCeramic scintillators are promising due to their potentially low cost. Here, we report on our study of Ce-doped ceramics. Typical garnet-type ceramics Gd2.97Ce0.03Al2Ga3O12 was fabricated for the ...study from co-precipitated powders by high-temperature sintering in air. Its structure and composition are characterized using Scanning Electron Microscope (SEM) imaging, Transmission Electron Microscopy (TEM), Electron Energy Loss Spectroscopy (EELS), Electron Backscattered Diffraction (EBSD) mapping, X-Ray Diffraction (XRD) and X-ray Absorption Near Edge Structure (XANES) measurements. The spatial distribution of luminescence properties at the micro-level is studied using scanning confocal microscopy. Cerium segregation at the grain boundaries was revealed by compositional characterization and is in line with enhanced Ce3+ photoluminescence observed at the boundaries. Meanwhile, no excess partitioning of Ce4+ ions at the grain boundaries is observed. It is found that most of Ce ions in the ceramics are stabilized in the state Ce3+, what is encouraging in view of the further development of GAGG:Ce ceramics as a promising luminescence material for lighting and scintillator application.
Display omitted
•Ce-doped garnet Gd2.97Ce0.03Al2Ga3O12 ceramics was fabricated by sintering in air.•Ce segregation at grain boundaries was shown by EELS.•Enhanced Ce3+ photoluminescence at grain boundaries was observed.•Ce ions were stabilized in +3 state mostly, shown by XANES and luminescence kinetics.•Sintering in presence of O2 allows to obtain luminescent garnet ceramics.
The aim of this work has been to improve the time resolution of radiation detectors for future high-energy physics experiments and medical imaging applications. Ce-doped oxyorthosilicate Lu2SiO5:Ce ...(LSO) and mixed oxyorthosilicate Lu1.6Y0.4SiO5:Ce (LYSO) have been investigated as prospective scintillators for such high-time-resolution applications. A differential optical absorption technique with sub-picosecond time resolution upon selective excitation of Ce3+ ions to different excited states has been adopted to study carrier dynamics in these scintillators, and coincidence time resolution measured using 511 keV γ-quanta has been exploited to test their timing properties. A delay in population of the emitting level of Ce3+ has been observed, and is interpreted in terms of electron trapping, which is more pronounced in mixed yttrium-containing LYSO crystals due to composition fluctuations. It is shown that the delay, which affects the luminescence response time, can be eliminated by co-doping of LYSO:Ce with calcium at concentrations as low as 5 ppm. The faster kinetics of electron transfer correlates with a better coincidence time resolution. Thermalization and spatial distribution of non-equilibrium carriers has been studied theoretically to link the results obtained by the time-resolved differential optical absorption technique with the behavior of the non-equilibrium carriers generated by irradiation.
•The time resolution of LYSO is more affected by carrier trapping than that of LSO.•Carrier trapping in LYSO is enhanced by fluctuations in the compound composition.•Ca-co-doping, even at a concentration of 5 ppm, improves the response time of LYSO:Ce.•Femtosecond pump-probe spectroscopy is a useful tool for improving Ce-doped scintillators.
The influence of co-doping of Gd3Al2GA3O12:Ce (GAGG:Ce) scintillator with magnesium on the rise time of luminescence response was studied in two GAGG:Ce crystals grown in nominally identical ...conditions except of Mg co-doping in one of them. Time-resolved photoluminescence spectroscopy and free carrier absorption techniques were exploited. It is evidenced that the Mg co-doping decreases the rise time down to sub-picosecond domain. Meanwhile, the light yield decreases by ∼20%. Thus, the feasibility of exploitation of the fast rise edge in luminescence response for ultrafast timing in scintillation detectors is demonstrated. The role of Mg impurities in facilitating the excitation transfer to radiative recombination centers is discussed.
•Photoluminescence rise time is compared in GAGG:Ce and GAGG: Ce,Mg.•Sub-picosecond photoluminescence rise time is revealed in GAGG:Ce,Mg.•The role of Mg in facilitating the excitation transfer is discussed.
Novel glasses and glass ceramics with compositions corresponding to stoichiometric lithium and barium disilicates and doped with different combinations of Ce3+, Eu2+,3+, Tb3+, and Dy3+ have been ...fabricated and studied as prospective light converters for white high-power light emitting diodes and laser diodes. Spatially resolved photoluminescence spectroscopy and structural analysis have been employed. The emission spectra and CIE color coordinates of these materials evidence their good prospective as phosphors for white light sources. Structural analysis proves a high level of crystallization of the ceramics fabricated by annealing the glasses, while spectroscopic study revealed the influence of crystallization on the emission properties of this system. The results show a high potential of these materials be exploited as temperature-resistant phosphors in high-power white light emitting diodes.
•Luminescence of BaO-2SiO2 and Li2O-2SiO2 systems doped with RE ions is studied.•Doping with combinations of Ce3+, Eu2+,3+, Tb3+, and Dy3+ is investigated.•Color properties of the glasses are studied.•Influence of crystallization on Eu ion emission is presented.
PDF
