A model of energy relaxation in alkali halide scintillators doped with Tl-like activators is presented. Interaction between thermalized charge carriers, their diffusion, and capture by traps are ...considered. The model of energy relaxation suggested in the work includes essential electron excited states in alkali halides doped with Tl-like activators. Self-trapping of holes occurs in alkali halides at LNT, giving rise to creation of self-trapped excitons (STEs). Thallium-like activator impurity can act both as an electron or a hole trap. Once both of the charge carriers are trapped by the dopant, activator recombination channel comes to action. The model is verified using CsI classical scintillation crystals doped with thallium and indium ions in a range of concentrations from 10–4 to 10–1 mol %. Temperature dependences of the STE and the activator-induced emission yield are measured as a function of the activator concentration under continuous X-ray excitation. A system of rate equations is used to simulate the applicability of the model under different excitation conditions. Evaluation of the parameters of the system is done for a numerical solution. The model of energy relaxation suggested allows to explain energy losses in CsI:A scintillators in a 10–300 K temperature range.
Undoped and Ce3+-doped Lu3Al5O12 (LuAG) fibers were grown to evaluate their potential use in new particle physics experiments, such as dual-readout calorimeters. The choice of grown crystals was made ...to detect scintillation (doped LuAG) and Cherenkov radiation (undoped LuAG). Growth conditions for obtaining fibers with improved quality were found based on measurements of attenuation length of the fibers and cathodoluminescence measurements. The effect of annealing on attenuation length for LuAG and LuAG:Ce was also studied. In addition, we also evaluated a possibility to substitute LuAG by the cheaper mixed and (Lu,Y)3Al5O12 (LuYAG:Ce) fibers.
•Undoped and Ce-doped LuAG fibers were grown by micro-pulling down technique.•Substitution of Lu3+ by Y3+ in (Lu1−xYx)3Al5O12 fibers improve Ce distribution.•Annealing of Ce-doped LuAG fibers improve the light propagation through the fibers.•Attenuation length over 1m can be achieved in LuAG:Ce after thermal annealing.
Thermally stimulated luminescence (TSL) measurements with spectral resolution on undoped NaI and NaI doped with Tl, In, and Eu are presented and analyzed. Based on the trap parameters extracted, ...carrier release rates are calculated as a function of temperature. The parameters calculated at 300 K by whole peak fitting yield release rates which are about 1–2 orders of magnitude higher than those obtained using the initial rise method. These data can be used to test release-rate predictions of the first ab initio calculations of carrier release and capture rates on dopants in NaI by Prange et al. A kinetic model of rate equations describing energy relaxation in NaI with different activators is used to simulate the TSL experiment and suggest an interpretation of the peaks’ origin(s). We found that thallium can trap either charge carrier, electron or hole, while indium is only a hole trap, and europium induces very shallow electron traps in NaI.
Optical absorption, luminescence spectra, scintillation decay curves, and scintillation light yield were measured in a series of undoped yttrium-aluminum garnet (YAG) crystals of different origins. ...This paper reveals a correlation between luminescent properties and scintillation efficiency of undoped YAG crystals. All the samples were separated into three groups, Type I, Type II, and Type III, based on their optical properties and scintillation efficiency. The intrinsic ultraviolet luminescence band peaking around 300 nm is found in the samples with high scintillation yield (Type I). Luminescence intensity of this band depends on the crystal purity and on the stoichiometry of the garnets. The UV emission may be related to e-h recombination in vicinity of vacancies. The garnets of Type II contain more impurities which quench the 300-nm emission. The samples of Type III do not exhibit any significant radioluminescence. Light yield of the finest undoped YAG samples in the series, Type I, is similar to the yield of Ce-doped YAG. This Type of crystals can potentially be used in scintillation detectors.
Scintillation properties of CsI:In single crystals Gridin, S.; Belsky, A.; Moszynski, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2014, Letnik:
761
Journal Article
Recenzirano
Scintillation properties of CsI:In single crystals have been investigated. Scintillation yield of CsI:In measured with the 24μs integration time is around 27,000ph/MeV, reaching the saturation at ...0.005mol% of the activator. However, luminescence yield of CsI:In is close to CsI:Tl scintillation crystals, which is around 60,000ph/MeV. This difference is explained by the presence of an ultra-long afterglow in CsI:In scintillation pulse. Thermoluminescence studies revealed a stable trap around 240K that is supposed to be related to millisecond decay components. The best measured energy resolution of (8.5±0.3)% was achieved at 24μs peaking time for a CsI sample doped with 0.01mol% of In. Temperature stability of CsI:In radioluminescence intensity was found to be remarkably high. Its X-ray luminescence yield remains stable up to 600K, whereafter thermal quenching occurs. The latter property gives CsI:In a potential to be used in well logging applications.
Radiative relaxation channels and energy losses in In and Tl doped CsI scintillation crystals have been investigated as a function of temperature and excitation conditions to evaluate scintillation ...efficiency of the activator channel. Two activator concentration series of crystals were grown by the Bridgman method. Temperature dependence of excitation and luminescence spectra were measured under VUV and X-ray excitation; thermostimulated luminescence was also studied. The observed drop of radioluminescence yield of doped CsI crystals at room temperature relative to the pure crystal is explained by the migration losses caused by charge carrier trapping on the activator centers. The energy losses in CsI:A at low temperatures are due to the trapping of charge carriers on different centers: self-trapping of holes and capture of electrons by the activator centers. We suppose that migration energy losses are the main reason for significantly lower luminescence yield of CsI:A at room temperature than that of self-trapped excitons in pure CsI crystal.
The influence of different activator impurities on the scintillation yield of alkali halides has been investigated as a function of temperature. Luminescence spectra of pure and activated CsI and NaI ...scintillation crystals were measured under X‐ray and VUV excitation at temperatures from 10 to 300 K. In indium‐ and thallium‐doped crystals activator centers can capture electrons. Along with self‐trapping of holes at low temperatures, electron capture by the dopant results in energy storage. This leads to a significant decrease of luminescence yield. In Eu‐doped NaI and CsI crystals activator centers capture a hole first. In this way, at low temperatures electrons recombine either with self‐trapped holes (yielding STE emission), or with holes trapped by the activator (giving rise to Eu emission band). No energy loss at low temperature is evident in CsI:Eu and NaI:Eu crystals.
Luminescence of color centers in the near-infrared region under cathode beam excitation is revealed for the first time in as-grown pure LiF and LiF:Mg,O crystals. Emission efficiency of F2+, F3− and ...F2−centers is higher for the samples enriched by oxygen and magnesium than for ultrapure crystals. The intensity of the NIR luminescence remains practically constant with the increase of the electron beam density. In contrast, visible emission typical for F3+and F2 centers is suppressed due to the induced absorption bands. It is assumed that the high-density electronic irradiation leads to the strongly pronounced thermal- and radiation-stimulated diffusion in a relatively thin layer. It causes the association of point radiation defects with the formation of various complex centers and aggregates. Results obtained suggest that LiF crystals can be used for in-situ detection of ionizing radiation.
► Color centers NIR emission is firstly revealed in LiF under the cathode excitation. ► F2+, F3− and F2− centers emission is higher for LiF:Mg,O than for pure LiF crystal. ► NIR emission intensity remains persistent with the increase of excitation density. ► Visible emission of F3+ and F2 and F2− centers is suppressed due to the induced absorption. ► Results obtained point to possibility of LiF for “in-situ” detection of radiation.
Ce-doped Lu2xGd2−2xSiO5 (LGSO:Ce) fiber-shaped crystals (x = 0.5) were grown by the micro-pulling down (µ-PD) technique. To optimize the activator concentration for achieving the best scintillation ...parameters, the cerium concentration in the melt was varied in the range from 0.01 to 1.5 at.%. Distributions of Gd3+ and Ce3+ in LGSO:Ce crystals grown by the µ-PD and Czochralski (Cz) techniques were compared. The spatial distribution of cations across the LGSO:Ce scintillation crystals grown by the µ-PD technique is studied using wide-field microscopy under simultaneous excitation of two types of Ce-related centers and confocal microscopy under the selective excitation of Ce3+ in CeO6 crystallographic sites. It is revealed that the fiber-shaped crystals contain a single crystal core surrounded by crystalline material with a higher density of inclusions and cracks that are predominantly directed along the crystal axis. The formation of inclusions and cracks is interpreted by a nonuniform radial distribution of LGSO:CE cations.
•Scintillation fibers of lutetium gadolinium orthosilicate doped with Ce3+ were grown by micro-pulling down technique.•We characterized the spatial distribution of cations using confocal microscopy.•Areas with increased activator concentration were revealed that are associated with the growth process.•We discuss potential reasons for cracking in these mixed crystals.
The work is devoted to the controlled crystal growth procedure providing of optimal doping of dielectric halide materials (LiF crystals in particular). Two series of LiF crystals were studied. One ...series is represented by ultra- and nominal pure crystals, as well as crystals doped with polyvalent oxides (Nb2O5, WO3 and TiO2), which were grown by classical Kyropoulos method in vacuum, second series involves crystals grown using the skull method. It is shown that the skull technique is a quite efficient method of variously doped LiF crystal growth as compare with the classic Kyropoulos method.
•Pure and doped LiF crystals grown by the Kyropoulos and Skull methods were studied.•UV–vis range and IR absorption spectra, excitation and luminescence spectra of pure and doped with Nb2O5, WO3 or TiO2 LiF crystals were studied.•We show that the skull technique is quite efficient method of variously doped LiF crystal growth.
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