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The development of hybrid nanoscintillators is hunted for the implementation of modern detection technologies, like in high energy physics, homeland security, radioactive gas sensing, and medical imaging, as well as of the established therapies in radiation oncology, such as in X-ray activated photodynamic therapy. Engineering of the physico-chemical properties of nanoparticles (NPs) enables the manufacture of hybrids in which the conjugation of inorganic/organic components leads to increased multifunctionality and performance. However, the optimization of the properties of nanoparticles in combination with the use of ionizing radiation is not trivial: a complete knowledge on the structure, composition, physico-chemical features, and scintillation property relationships in hybrid nanomaterials is pivotal for any applications exploiting X-rays. In this paper, the design of hybrid nanoscintillators based on ZnO grown onto porous SiO2 substrates (ZnO/SiO2) has been performed in the view to create nanosystems potentially suitable in X-ray activated photodynamic therapy. Indeed, cytotoxic porphyrin dyes with increasing concentrations have been anchored on ZnO/SiO2 nanoparticles through amino-silane moieties. Chemical and structural analyses correlated with photoluminescence reveal that radiative energy transfer between ZnO and porphyrins is the principal mechanism prompting the excitation of photosensitizers. The use of soft X-ray excitation results in a further sensitization of the porphyrin emission, due to augmented energy deposition promoted by ZnO in the surroundings of the chemically bound porphyrin. This finding unveils the cruciality of the design of hybrid nanoparticles in ruling the efficacy of the interaction between ionizing radiation and inorganic/organic moieties, and thus of the final nanomaterial performances towards the foreseen application. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate the influence of shallow traps on scintillating properties of YAl[O.sub.3] : Ce. Wavelength-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 YAl[O.sub.3] : Ce, their room temperature decay time was evaluated to be of the order of [10.sup.-4] s. The presence of an athermal tunneling recombination process between traps and [Ce.sup.3+] ions below 100 K has been evidenced by phosphorescence decays. Index Terms--Perovskites, scintillators, thermally stimulated luminescence, YAP.

The optical absorption, luminescence and scintillation characteristics of [Lu.sub.3][Al.sub.5][O.sub.12]:Ce optical ceramics are measured and compared with an analogous high quality single crystal. The results have shown that the optical and scintillation characteristics of LuAG:Ce ceramic samples have shown higher figure of merit in OC2 samples when compared to OC1 samples.

We have studied the color-center production in sapphire and yttria-stabilized zirconia (YSZ) single crystals by cathodo-luminescence (CL) spectroscopy for electron energies ranging between 400 and 1250 keV in a high-voltage electron microscope. Emission spectra were collected for in-beam conditions near room temperature and at 200 K. Comparison was made with CL spectra recorded for 3-keV-20-keV electrons in a scanning electron microscope. For high-energy electrons, CL spectra for sapphire revealed broad emission bands centered at photon energies about 3.0 eV and 3.8 eV that were, respectively, assigned to oxygen vacancies (F0 and F+ centers) induced by elastic collisions, on the basis of photoluminescence (PL) data. No such bands were recorded for 3-keV and 5-keV electrons. Two similar bands were also recorded for YSZ (with 9.5 and 18 mol. % yttria) at about 2.8 eV and 4.1 eV that can be, respectively, attributed to the native oxygen vacancies (F2+ centers) and F+ centers. The 4.1-eV band was not seen for 20-keV electrons: it was only produced for high electron energies by elastic collision processes. Instead, the small side band was also found at 2.85 eV for 20-keV electrons. PL excitation contour plots of virgin and irradiated YSZ were also recorded to support our discussion on point-defect identification. CL band intensities show a maximum versus electron energy, whereas point-defect concentrations should increase due to the increase of oxygen atom displacement cross section. The effect of electron energy on the different steps of the CL process is discussed to account for such a behavior. [ABSTRACT FROM AUTHOR]

Lead halide perovskites (LHP) are rapidly emerging as efficient, low‐cost, solution‐processable scintillators for radiation detection. Carrier trapping is arguably the most critical limitation to the scintillation performance. Nonetheless, no clear picture of the trapping and detrapping mechanisms to/from shallow and deep trap states involved in the scintillation process has been reported to date, as well as on the role of the material dimensionality. Here, this issue is addressed by performing, for the first time, a comprehensive study using radioluminescence and photoluminescence measurements side‐by‐side to thermally‐stimulated luminescence (TSL) and afterglow experiments on CsPbBr3 with increasing dimensionality, namely nanocubes, nanowires, nanosheets, and bulk crystals. All systems are found to be affected by shallow defects resulting in delayed intragap emission following detrapping via a‐thermal tunneling. TSL further reveals the existence of additional temperature‐activated detrapping pathways from deeper trap states, whose effect grows with the material dimensionality, becoming the dominant process in bulk crystals. These results highlight that, compared to massive solids where the suppression of both deep and shallow defects is critical, low dimensional nanostructures are more promising active materials for LHP scintillators, provided that their integration in functional devices meets efficient surface engineering. [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]

A better understanding of the physical mechanisms and point defects involved in quartz's charge trapping and luminescence processes enables improving the luminescence dating and dosimetry applications relying on this mineral. Here we report on the progress in our systematic investigation of two reference quartz samples using various spectroscopic techniques [1]. One sample originates from the "Silver Sands of Morar", Scotland -- UK, and the other one from the Oligocene Fontainebleau Sandstone Formation, France. We conducted wavelength-resolved thermally stimulated luminescence (WR-TSL) measurements over an extended temperature range, from 10 K to 630 K, to point out similarities and differences between the luminescence properties of the two samples. We identified various luminescence emission bands, studied their correlation with specific TSL traps and compared the results with the data reported in the literature. We will show which emission bands previously evidenced by X-ray radioluminescence (RL) measurements are also detectable in TSL emission spectra [2]. In particular, we focus on the so-called 190 K TSL peak, which has been correlated to the [SiO4/Li]0 centres and is known to display a pre-dose-like behaviour analogously to the 110 °C peak, resulting in an enhancement of their UV emission [3]. We attempt to determine which of the previously reported UV bands, i.e., the 3.42 eV emission (C band) or the 3.73 eV one (M band), is enhanced in the pre-dose, like sensitization of the 190 K peak. Finally, we report RL measurements over the range of 10 K -- 320 K to determine the temperature dependence of the luminescence emissions and quantify the contribution of the self-trapped exciton (STE) band. The results obtained, together with the data reported on the same samples in previous works, provide a more comprehensive picture of the luminescence properties of these reference materials. The data will be discussed in relation to experimental results reported in the literature on different types of quartz. [ABSTRACT FROM AUTHOR]

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]

Yttria-stabilized zirconia (YSZ) single crystals (for 9.5 and 18 mol% yttria) were irradiated at room temperature (RT) by X-rays (W white spectrum) and 2.5-MeV electrons. The growth curves of the so-called T-centre (for trigonal centre, i.e. Zr3+sitting in a trigonal symmetry site) were studied as a function of absorbed dose, or irradiation time, by UV–visible optical absorption (OA) spectroscopy and X-band electron paramagnetic resonance spectroscopy. The defect concentration at saturation and the production rate are increased by a factor around two for 18 mol% yttria with respect to 9.5 mol%. Defect decay was then followed after irradiation by OA spectroscopy as a function of ageing time at RT. Growth and decay curves of the T-centre are modelled on the basis of rate equations of charge-exchange reactions with the zirconium lattice ions. Increase in yttrium content is thought to decrease hole trapping on Zr3+ions, thereby enhancing T-centre formation. [ABSTRACT FROM AUTHOR]

Radio-luminescence (RL) optical fiber sensors enable a remote, punctual, and real time detection of ionizing radiation. However, the employment of such systems for monitoring extended radiation fields with energies above the Cerenkov threshold is still challenging, since a spurious luminescence, namely, the "stem effect," is also generated in the passive fiber portion exposed to radiation. Here, we present experimental measurements on Yb-doped silica optical fibers irradiated with photon fields of different energies and sizes. The results demonstrate that the RL of Yb3+, displaying a sharp emission line at about 975 nm, is free from any spectral superposition with the spurious luminescence. This aspect, in addition with the suitable linearity, reproducibility, and sensitivity properties of the Yb-doped fibers, paves the way to their use in applications where an efficient stem effect removal is required. [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]

Abstract: Spectrally resolved thermoluminescence (TL) of non-doped and Ag, Cu− and Mn-doped lithium-tetraborate (LTB) single crystals revealed that TL emission bands for differently doped samples proved to be at different wavelengths: 272, 370 and 608nm, respectively. These bands perfectly agree with the photoluminescence (PL) emission bands of Ag+, Cu+ and Mn2+ ions. It strongly points that these dopants are directly involved as recombination centers in the TL process. TL characteristics of non-doped and doped LTB single crystals and the corresponding glassy samples showed that their TL intensities and the structures of the glow curves were apparently different. [Copyright &y& Elsevier]

The search for new materials which could be used as scintillating bolometers is a subject of great interest in view of next-generation experiments dedicated to the study of neutrinoless double beta decay (DBD). Preliminary measurements performed on ZnSe bolometric and scintillation characteristics gave very promising results for what concerns the amplitude of the scintillation signal and the capacity to discriminate between á and â particles. The current work studies the possibility to develop a scintillating ZnSe crystal adapted for the use as hybrid (thermal and scintillation) detector operating at very low temperatures (< 20 mK), able to discriminate between á and â induced events. The results of optical transmission, X-ray excited steady-state luminescence and thermo-luminescence measurements performed on ZnSe crystals produced in different conditions are presented. Based on these measurements, the scintillation properties of undoped ZnSe crystals are carefully described. The correlation between these measurements and bolometric/scintillation tests is used in order to fix the production conditions of ZnSe crystals which best guarantee scintillation efficiency at very low temperatures for possible use in a DBD experiment. [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]

This study addresses the relationship between material morphology (size, growth parameters and interfaces) and optical emissions in ZnO through an experimental approach, including the effect of different material dimensions from bulk to nano-size, and different excitations, from optical sources to ionizing radiation. Silica supported ZnO nanoparticles and ligand capped ZnO nanoparticles are synthesized through a sol–gel process and hot injection method, respectively. Their optical properties are investigated by radioluminescence, steady-state and time-resolved photoluminescence, and compared to those of commercial micrometric powders and of a bulk single crystal. The Gaussian spectral reconstruction of all emission spectra highlights the occurrence of the same emission bands for all samples, comprising one ultraviolet excitonic peak and four visible defect-related components, whose relative intensities and time dynamics vary with the material parameters and the measurement conditions. The results demonstrate that a wide range of color outputs can be obtained by tuning synthesis conditions and size of pure ZnO nanoparticles, with favorable consequences for the engineering of optical devices based on this material. [ABSTRACT FROM AUTHOR]

The 15th International Conference on Inorganic Scintillators and Their Applications (SCINT 2019) was organized by Tohoku University, and held in Sendai, Japan, September 29–October 4, 2019. A total of 246 colleagues from 24 different countries finally participated in the conference. The program consisted of seven keynote invited and four invited lectures, and 61 oral and 88 poster contributions. Extended exhibitions with 12 exhibitor stands altogether provided another link to the market applications behind the research. An intense and structured research and development in the field of scintillators was represented by 13 sessions oriented toward various material technologies, including nanomaterials, metamaterials, and classical bulk single crystals and optical ceramics. Their characterization, modeling, and underlying physical mechanisms description constituted the subject of the major part of conference contributions. Finally, various applications of inorganic scintillators were also presented and discussed. [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]