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Radio- and thermoluminescent properties of HfO 2 :Ti sintered ceramics were investigated in the temperature range of 10–300 K. Fabrication atmosphere altered somewhat the efficiency of radioluminescence but did not affect the spectral distribution of the broad scintillation band covering the 380–570 nm range of wavelengths and peaking at 522 nm at 10 K and about 490 nm at 300 K. The analogous shift was seen in photoluminescence. Scintillation efficiency was continuously growing from 10 K to 300 K, while photoluminescence intensity was stable in the 10–250 K range of temperatures and was reduced by about 30% at 300 K. Analysis of these observations allowed to conclude that diffusion of carriers generated upon the impact of high-energy photons towards the Ti emitting center is strongly temperature-dependent and inferior at lower temperatures. Upon exposure to X-rays at 10 K the ceramics stored more than 50% of the absorbed energy. This energy could be recovered later upon thermal stimulation of the ceramics. Four main thermoluminescent peaks were then produced at 95, 140, 243 and 278 K. This effect was tentatively associated with theoretically predicted self-trapping of holes in HfO 2 . The so-called partial cleaning and T max –T stop experiments indicated that some fraction of traps shows a continuous distribution of their depths. [ABSTRACT FROM AUTHOR]

Abstract: BGO crystals have been grown using the Czochralski method by the West Pomeranian University of Technology in Szczecin, Poland. We report the measurements of scintillation yield and low temperature thermoluminescence, performed on polished 2×2×10mm3 pixel and 2×2×2mm3 cube samples. The yield of the pixels placed horizontally on the PMT window, as well as of the cubes, is about twice higher than the yield of the pixels placed vertically. Such a distinct light loss is interpreted in the frame of a simple two-ray model, describing quantitatively the scintillation yield of pixel samples depending on the measurement geometry. Related to this effect, the common overuse of “BGO units” for expressing the light output of any scintillator is discussed. Thermoluminescence glow curves consist of several peaks attributed to the existence of traps, which turn out to be responsible for a slight decrease of the scintillation yield measured at room temperature in a short time window. To improve the performance of BGO crystals, efforts should be aimed at reducing both the internal light losses and the trap concentration, with the main emphasis laid on the former. [Copyright &y& Elsevier]

Abstract: BaF2:Ce scintillator is a well-known, reasonably fast and efficient scintillator characterized by a decent stopping power and availability of large size crystals. In this communication we report scintillation light yield measurements on a number of BaF2:Ce samples cut from one larger boule. We interpret these measurements in a frame of a simple one-dimensional model developed and first tested on LuAP and LuYAP samples. The model is expected to reproduce the observed strong dependence of the effective scintillation light yield against the height of the sample. The fit to experimental points provides a value of the “intrinsic” light yield LY(0), as well as a value of the “loss” parameter μ (scattering and absorption of scintillation light in the sample). Although the value of the loss parameter μ, at around 0.5cm−1, found from the fit for BaF2:Ce is clearly lower than a typical value in LuAP and LuYAP, it is, nevertheless, much higher than the value of about 0.05–0.07cm−1 measured in Delft for LaBr3:Ce. We have also measured the absorption spectra of BaF2:Ce crystals. The corrected spectra have been used to estimate contributions from scattering, self-absorption (by Ce-ions) and parasitic absorption from unidentified centers in order to establish physical limits imposed on the light yield from these crystals. [Copyright &y& Elsevier]

Abstract: In the last 10–15years there has been a significant effort toward development of new, more efficient and faster materials for detection of ionizing radiation. A growing demand for better scintillator crystals for detection of 511keV gamma particles has been due mostly to recent advances in modern imaging systems employing positron emitting radionuclides for medical diagnostics in neurology, oncology and cardiology. While older imaging systems were almost exclusively based on BGO and NaI:Tl crystals the new systems, e.g., ECAT Accel, developed by Siemens/CTI, are based on recently discovered and developed LSO (Lu2SiO5:Ce, Ce-activated lutetium oxyorthosilicate) crystals. Interestingly, despite very good properties of LSO, there still is a strong drive toward development of new scintillator crystals that would show even better performance and characteristics. In this presentation we shall review spectroscopic and scintillator characterization of new complex oxide crystals, namely LSO, LYSO, YAG, LuAP (LuAlO3, lutetium aluminate perovskite) and LuYAP activated with Ce and Pr. The LSO:Ce crystals have been grown by CTI Inc (USA), LYSO:Ce, LuAP:Ce and LuYAP:Ce crystals have been grown by Photonic Materials Ltd., Scotland (PML is the only company providing large LuAP:Ce crystals on a commercial scale), while YAG:Pr and LuAP:Pr crystals have been grown by Institute of Electronic Materials Technology (Poland). All these crystals have been characterized at Institute of Physics, N. Copernicus University (Poland). We will review and compare results of measurements of radioluminescence, VUV spectroscopy, scintillation light yields, scintillation time profiles and low temperature thermoluminescence performed on these crystals. We will demonstrate that all experiments clearly indicate that there is a significant room for improvement of LuAP, LuYAP and YAG. While both Ce-activated LSO and LYSO perform very well, we also note that LuYAP:Ce, LuAP:Ce and YAG:Pr offer some advantages and, after a likely improvement of some parameters, may also present a viable and desired alternative in applications that require high counting rates or better time resolution. Unfortunately, LuAP:Pr, although the fastest among all the materials studied, may be seriously limited in its achievable light yield by inherent physical processes that are responsible for nonradiative quenching of scintillation light in this material. [Copyright &y& Elsevier]

In recent years, the scintillation properties of several cerium-doped rare earth oxyorthosilicate scintillators, Ln2SiO5:Ce where Ln = Y, La-Lu, have been reported and, in some cases, extensively studied [11-[31. In addition, binary and ternary compounds such as (Lu,Y)2SiO5:Ce, (Lu,Gd)2SiO5 and (Lu,Y,Gd)2SiO5 :Ce have been reported [3]-[7]. All of these crystals have either monoclinic P or C structures with characteristic SiO4 tetrahedra and trivalent cations occupying two unique crystallographic positions [8], [9]. The trivalent cerium activator ions are assumed to occupy the cation lattice sites and possibly interstitial positions as well. The excited Sd state of Ce3+ is split into three observable levels with luminescence emission occurring only from the lowest 5d level to the 4f ground state (∼3 eV) with a Stokes shift of ∼0.5 eV. The bandgap is about 6 eV, and the index of refraction is close to 1.8, with some variation according to crystallographic direction. Despite these similarities, in somecases, differences in scintillation efficiency, decay time, rise time, and phosphorescence time profiles have been observed. In this paper, we combine thermoluminescence measurements with the temperature characteristic of scintillation efficiency between 10 and 350 K to determine the trapping levels that may influence the scintillation and phosphorescence properties of crystals of various compositions. [ABSTRACT FROM AUTHOR]

Parity-allowed UV 5d–4f transitions characterized by a high oscillator strength make trivalent cerium an interesting activator for fast and efficient scintillator crystals. Indeed, several materials are known, in which the radiative lifetime of the Ce3+ ions is shorter than 20 ns (e.g. LuAlO3:Ce and YAlO3:Ce). For the case of BaF2:Ce, however, the value of 27 ns is known from literature. In this communication we show that the 5d–4f luminescence in BaF2:Ce is in fact faster. Having analyzed several series of time profiles recorded at various temperatures between 25 and 350 K, we conclude that the true radiative lifetime of the Ce3+ ions in BaF2 is close to 20 ns and it is the radiation trapping caused by the temperature-dependent reabsorption of cerium emission which prolongs the effective decay time. [Copyright &y& Elsevier]

Open f-shell rare-earth (RE) ions in wide bandgap host materials are usually characterized by closely spaced electronic levels due to various electron configurations and charge states. These levels provide convenient luminescent transitions that can be excited by efficient recombination of charge carriers generated in the host material by ionizing radiation. Therefore, it is the area of ionizing radiation detectors, where search for new, fast and efficient scintillator materials for high-energy physics and nuclear medicine, has yielded much of the recent advances in the understanding of radioluminescence and scintillation mechanism in some solid state, UV and VUV luminescent, RE-activated materials. In this paper we shall present selected results of basic experiments such as radioluminescence, VUV spectroscopy, time profiles and thermoluminescence, on barium fluoride (activated with Ce, Pr, Nd, Tb) and two aluminum perovskites, YAlO3 and LuAlO3, activated with Ce. We shall demonstrate that these results point to consecutive carrier capture and recombination at RE ions as the basic mechanism of radioluminescence and scintillation in these materials, despite the strong self-trapping and poor charge transport properties. Consequently, various electron and/or hole traps that intercept and retain for some time the recombining charge carriers play an active role influencing both the scintillation light yield and time profiles of scintillation pulses in these and many other wide bandgap RE-activated luminescent materials. [Copyright &y& Elsevier]

The SCINT series of conferences on Inorganic Scintillators and their Applications has provided, beginning in 1992, a regular platform for researchers from all over the world working in this field. This conference merges the aspects of basic science with application-related issues in the field of inorganic scintillators and phosphors and provides unique opportunities for both scientists and engineers to exchange their new results and ideas. Previous SCINT conferences were held first in Chamonix in 1992 and then in San Francisco, Delft, Shanghai, Moscow, Chamonix, Valencia, Alushta, Winston- Salem, and Jeju Island in Korea in 2009. The most recent, the 11th International Conference on Inorganic Scintillators and their Applications (SCINT 2011), was held at the Science Campus of Justus Liebig University, Giessen, Germany, September 11?16, 2011. There were a total 187 scientific contributions, 82 oral presentations, 19 invited talks, and 105 poster exhibitions presented by 235 participants from 24 different countries. For the first time, a pre-conference tutorial was organized, which covered the basic physics of scintillation mechanisms as well as the wide field of applications. The purpose was mainly to educate students and newcomers in the field. This special issue of the IEEE TRANSACTIONS ON NUCLEAR SCIENCE comprises the refereed proceedings of SCINT 2011, containing 61 papers on the research presentations. [ABSTRACT FROM PUBLISHER]

Low temperature thermoluminescence of GAGG:Ce and LuAG:Pr scintillator crystals has been studied by means of the Tmax-Tstop method. It is shown that the glow curves of both materials are superpositions of discrete glow peaks and broad bands due to quasi-continuous Gaussian distributions of trapping levels. A model function has been built and trap parameters have been evaluated. [ABSTRACT FROM AUTHOR]

Abstract β-Ga 2 O 3 and β-Ga 2 O 3 :Ce crystals have been grown by the Czochralski method and their scintillation properties have been studied by means of pulse height, radioluminescence and scintillation time profile measurements. It is shown that although the scintillation of β-Ga 2 O 3 :Ce is related to intrinsic excitonic emission, the doping with Ce improves some characteristics of the material. The prominent samples of β-Ga 2 O 3 :Ce display fast 6 ns (40%) scintillation, with total light yields of about 5000 ph/MeV. Highlights • β-Ga 2 O 3 and β-Ga 2 O 3 :Ce crystals have been grown by the Czochralski method. • Semiconducting samples (pure and Ce-doped) scintillate with yields of ∼5000 ph/MeV. • Doping with Ce improves some properties of β-Ga 2 O 3. [ABSTRACT FROM AUTHOR]

Due to their very fast short-wavelength emission, neodymium-doped materials are a subject of current interest as potential scintillators. Although the initial reports regarding neodymium-doped orthophosphates (in crystalline form) and their scintillation properties appeared almost twenty years ago, they remain an interesting class of materials since there is no in-depth understanding of their fundamental scintillation mechanism. In the present research, we focus on the crystalline systems: XPO 4 :Nd 3+ , where X = Y, Lu, La, Sc. The pulse height, optical absorption, radioluminescence and photoluminescence spectra were investigated and are reported here for various temperatures from 10 to 350 K. Additionally, results of both low and high temperature thermoluminescence measurements are reported in this communication. [ABSTRACT FROM AUTHOR]

Lu 2 Y 2 Al 2 O 9 :Pr crystals have been grown by the micro-pulling-down method and their basic luminescence properties have been examined in order to estimate their utility for scintillator applications. The performed studies comprise the measurements of radioluminescence spectra as a function of temperature, photoluminescence emission and excitation spectra, and low temperature thermoluminescence glow curves. A comparison of the present results with those obtained recently for Y 4 Al 2 O 9 :Pr indicates that in spite of a higher density Lu 2 Y 2 Al 2 O 9 :Pr is a much less promising material, which is mainly due to the absence of the fast Pr 3+ d-f emission. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of light yield, low temperature thermoluminescence, and scintillation time profiles, performed comparatively on “as grown” and thermally annealed LuAG:Pr samples, are reported. It is shown that traps play an efficient role in the scintillation of LuAG:Pr, being responsible for the yield decrease and introducing a long component to the time profiles. The trap concentrations in the annealed crystals are lower than in the non-annealed ones, which correlates with the yield enhancement. [Copyright &y& Elsevier]

Our recent research on scintillation properties of β-Ga 2 O 3 crystals, either pure or singly-, doubly-, and triply-doped, obtained with the Czochralski method at the Leibniz-Institut für Kristallzüchtung, is summarized. The results of pulse height, scintillation time profile, and low temperature thermoluminescence measurements are analyzed, mostly in reference to the values of free electron concentration in the samples. Some correlations between particular parameters are found and discussed in order to give hints for a further development of the material. • Czochralski-grown pure and doped β-Ga2O3 have been characterized. • Scintillation yield and decay times strongly depend on free electron concentration. • Glow curve shapes have been interpreted based on a simple two-electron-trap model. [ABSTRACT FROM AUTHOR]

β-Ga 2 O 3 is an emerging ultra-wide bandgap (4.9 eV) oxide semiconductor that additionally scintillates under gamma excitation. A unique combination of transparency in the UV/visible spectrum, semiconducting, and scintillation properties makes that compound interesting for fundamental studies of underlying physics and design of novel devices, in particular compact detectors for gamma radiation. Undoped, and singly (Ce, Si, Al), doubly (Ce + Si, Ce + Al), and triply (Ce + Al + Si) doped bulk β-Ga 2 O 3 single crystals were grown by the Czochralski method under very similar conditions and systematically studied in terms of electrical and optical properties that were correlated with scintillation light yield under gamma excitation. A wide spectrum of doping enabled to control the free electron concentration in semiconducting β-Ga 2 O 3 crystals within almost three orders of magnitude (7 × 1015–6 × 1018 cm−3) with the Hall mobility approaching 150 cm2 V−1s−1. The maximum of light yield under gamma excitation was recorded for undoped and Ce-doped β-Ga 2 O 3 single crystals having the free electron concentration of mid 1016 cm−3. The light yield significantly decreases for both electrically insulating and highly conducting (Si-doped) crystals. None of the dopants (Ce, Si, Al) introduces any absorption bands in the spectral region of light emission (340–410 nm) under gamma excitation. The dopants in quest do not affect the structure of neither cathodoluminescence (CL) nor radioluminescence (RL) emissions, but modify their absolute intensity. A double-band structure of RL spectra corresponds to UV and blue emissions observed in CL spectra that are assigned to self-trapped excitons. Image 1 • Doped semiconducting β-Ga 2 O 3 was grown and studied for gamma radiation detection. • The crystals are fully transparent to scintillation emissions at 340–410 nm. • Maximum of light yield was found at free electron concentration of mid 1016 cm−3. • Luminescence spectra point to self-trapped excitons in scintillation mechanism. [ABSTRACT FROM AUTHOR]