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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.

The coupling of ZnO-based nanomaterials with organic photosensitizers (PS) is potentially interesting for cancer treatment under X-ray. In these conditions, ZnO nanoparticles (NPs) convert the X-ray into UV-Vis emission, promoting the PS excitation and producing reactive oxygen species (ROS). Main advantages for in vivo applications are ZnO photostability and biocompatibility, even if its efficient coupling with different PS (typically porphyrin) is still a controversial issue, as both a high ZnO luminescence yield and a good overlapping of ZnO emission-PS absorption spectra are necessary, along with a suitable energy transfer between ZnO and PS. In this perspective, the aim is the investigation of the optical properties of an ad-hoc system composed of porphyrin functionalized ZnO NPs anchored on SiO2 NPs (ZnO/SiO2). The goal is the understanding of the optimal conditions for a good energy transfer efficiency of ZnO-porphyrin structures, including the role of ZnO-PS proximity, to promote their application in anti-cancer therapies and imaging with ionizing radiations. First, amorphous ZnO NPs of 5-6 nm were anchored onto SiO2 NPs (~80 nm); then, ZnO/SiO2 was functionalized with different porphyrin contents (tetrakis(4-carboxyphenyl)porphyrin, TCPP, 0.3 – 3.0 wt%) by exploiting a silane grafting agent (3-aminopropyl)triethoxysilane. The structural characterization demonstrated that increasing TCPP amounts were bonded to SiO2 depending on the TCPP loading. The optical properties were preliminary tested in dimethylformamide, used as solvent reaction for TCPP anchoring on SiO2. The Photoluminescence Analysis (PL) revealed a high luminescence of ZnO NPs and the occurrence of a radiative energy transfer between ZnO and TCPP, that was not visible in a mechanical mixing of ZnO and TCCP, highlighting their optical interaction upon functionalization. Besides, TCPP emission was hugely enhanced under X-ray in the Radioluminescence (RL), whereas no enhancement was detectable in t

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.

We report here the synthesis of undoped and Cu-doped Cs2ZnCl4 nanocrystals (NCs) in which we could tune the concentration of Cu from 0.7 to 7.5%. Cs2ZnCl4 has a wide band gap (4.8 eV), and its crystal structure is composed of isolated ZnCl4 tetrahedra surrounded by Cs+ cations. According to our electron paramagnetic resonance analysis, in 0.7 and 2.1% Cu-doped NCs the Cu ions were present in the +1 oxidation state only, while in NCs at higher Cu concentrations we could detect Cu(II) ions (isovalently substituting the Zn(II) ions). The undoped Cs2ZnCl4 NCs were non emissive, while the Cu-doped samples had a bright intragap photoluminescence (PL) at similar to 2.6 eV mediated by band-edge absorption. Interestingly, the PL quantum yield was maximum (similar to 55%) for the samples with a low Cu concentration ([Cu] <= 2.1%), and it systematically decreased when further increasing the concentration of Cu, reaching 15% for the NCs with the highest doping level ([Cu] = 7.5%). The same (similar to 2.55 eV) emission band was detected under X-ray excitation. Our density functional theory calculations indicated that the PL emission could be ascribed only to Cu(I) ions: these ions promote the formation of trapped excitons, through which an efficient emission takes place. Overall, these Cu-doped Cs2ZnCl4 NCs, with their high photo- and radio-luminescence emission in the blue spectral region that is free from reabsorption, are particularly suitable for applications in ionizing radiation detection.

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 106–1017 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.

The general behaviour of the main UV emission during radiofluorescence (RF) in natural quartz with dose rates ranging from 10 to 500 mGy s−1is analysed. RF emission spectra were recorded and deconvolved to extract information on the C band, which is often the main emission of quartz annealed at a temperature close to 500 °C. Our results confirmed theoretical findings, e.g., the direct proportionality of the initial RF signal of the C band with dose rate and the direct proportionality of the initial slope with the squared dose rate. Furthermore, numerical simulations employing a three-energy-level model and experimental data are in agreement. A first concept of using quartz UV-RF for dosimetric application is given based on the findings that different absorbed doses resulting from different dose rates match well into a single UV-RF decay curve

Electronic doping of colloidal semiconductor nanostructures holds promise for future device concepts in optoelectronic and spin-based technologies. Ag+ is an emerging electronic dopant in iii-v and ii-vi nanostructures, introducing intragap electronic states optically coupled to the host conduction band. With its full 4d shell Ag+ is nonmagnetic, and the dopant-related luminescence is ascribed to decay of the conduction-band electron following transfer of the photoexcited hole to Ag+. This optical activation process and the associated modification of the electronic configuration of Ag+ remain unclear. Here, we trace a comprehensive picture of the excitonic process in Ag-doped CdSe nanocrystals and demonstrate that, in contrast to expectations, capture of the photohole leads to conversion of Ag+ to paramagnetic Ag2+. The process of exciton recombination is thus inextricably tied to photoinduced magnetism. Accordingly, we observe strong optically activated magnetism and diluted magnetic semiconductor behaviour, demonstrating that optically switchable magnetic nanomaterials can be obtained by exploiting excitonic processes involving nonmagnetic impurities.

The optical emission from the 5d - 4f allowed transition of Pr3+ ions embedded in sol-gel silica is investigated for High Energy Physics applications requiring fast scintillating materials. A complete and detailed characterization of the optical, scintillation and radiation hardness properties of Pr-doped silica is carried out employing different experimental techniques including steady-state and time-resolved photo-luminescence, radio- and thermo-luminescence, scintillation and optical absorption. Optical absorption measurements, performed after X-ray irradiation sequences up to 1 kGy, evidence the formation of radiation-induced absorption bands related to point defects acting as color centers. Spontaneous partial recovery of the radiation-induced defects at room temperature, as well as after thermal treatments, is also disclosed. Particular attention is paid to the comparison between bulk silica, both before and after a melting process, and fibers. The results reveal the presence of a lower concentration of optically active defects in melted glass. Such comparison highlights a role of the fiber drawing in modifying the glass defectiveness, consisting in the occurrence of a structural reorganization of the amorphous network during the process

The identification of the center acting as electron source for the well-known 110 °C thermoluminescence (TL) peak of quartz is of fundamental importance for practical applications in dating and dosimetry. This TL peak was studied in parallel with the electron paramagnetic resonance (EPR) signal of the [GeO4]− center on natural colourless quartz irradiated at room temperature. Immediately after irradiation, the signals of the 110 °C TL peak and of [GeO4]− center decay exponentially in the same way, yielding a lifetime of 50.4 ± 0.9 min at room temperature. Besides, we acquired the isothermal decay curves for the 110 °C TL peak and [GeO4]− center at different temperatures (the samples were held at the selected temperature in the range of 260–308 K). The lifetimes extracted by the isothermal decays were plotted as a function of reciprocal temperature, revealing again the same behavior of the 110 °C TL peak and [GeO4]− center, both characterized by activation energies very close of 0.76 ± 0.07 eV and 0.77 ± 0.07 eV, respectively. All results of the present work clearly show the role of electron source of [GeO4]− center in the emission mechanism of the 110 °C TL peak in quartz.

A series of Sm3+ doped Lu2O3 nanoparticles have been synthesized via a simple co-precipitation method using oxalic acid as precipitant. The obtained compounds showed a platelet-like morphology with diameter ranging between 10 and 14 nm. The cell parameters increased with the increase of doping, due to the substitution of Lu3+ with larger Sm3+; also a progressive increase of the lattice strain has been induced. Sm3+ doped Lu2O3 nanoparticles showed interesting Vis and NIR emission, which was carefully evaluated together with lifetime measurements. In particular, the system with the lowest Sm3+ loading exhibited the best photoluminescence performances. Preliminary cell viability test evidenced that Sm3+ doped Lu2O3 nanoparticles are not toxic, underlining their potential application a NIR luminescent probes in bioimaging.

Over the years, many efforts have been made to develop radiation detectors to handle the complex issues of small field dosimetry and achieve the increasing accuracy, precision and in vivo dose monitoring required by the new advanced treatment modalities. In this context, interest has surged in the development of sensors based on scintillating optical fibres. In this paper, the near-infrared radioluminescence and dosimetric properties of Yb-doped silica optical fibres, coupled with a laboratory prototype based on an avalanche photodiode, were studied by irradiating the fibres with photons and electron beams generated by a Varian Trilogy accelerator. The performance of the system in standard and small field sizes has also been investigated, comparing the output factor, percentage depth dose and off-axis ratio measurements of the prototypal detector with other commercial sensors, including the Exradin W1 scintillator. The results of this study demonstrate that the drawback due to the stem effect in Yb-doped silica optical fibres can be managed in a simple but effective way by optical filtering. The robustness of the system in complex dosimetric scenarios and the accuracy and precision achieved by Yb-doped fibres in relative dose assessments suggest an effective use of the system for real-time in vivo dosimetry applications

FLARES is an innovative project in the field of rare events searches, such as the search for the neutrinoless double beta decay. It aims at demonstrating the high potential of a technique that combines ultra-pure scintillating crystals with arrays of high performance silicon drift detectors, operated at about 120. K, to reach a 1% level energy resolution. The proposed technique will combine in a single device all the demanding features needed by an ideal experiment looking for rare events. The performance of a first production of matrices of silicon drift detectors as well as first measurements of the low temperature light yield of a selection of high purity scintillating crystals will be presented and discussed

Defect engineering operated on metal oxides by chemical and structural modifications may strongly affect properties suitable for various applications such as photoelectrochemical behavior, charge transport, and luminescence. In this work, we report the tunable optical features observed in undoped monoclinic HfO2 nanocrystals and their dependence on the structural properties of the material at the nanoscale. Transmission electron microscopy together with X-ray diffraction and surface area measurements were used to determine the fine structural modifications, in terms of crystal growth and coalescence of crystalline domains, occurring during a calcination process in the temperature range from 400 to 1000 °C. The fit of the broad optical emission into spectral components, together with time-resolved photoluminescence, allowed us to identify the dual nature of the emission at 2.5 eV, where an ultrafast defect-related intrinsic luminescence (with a decay time of a few nanoseconds) overlaps with a slower emission (decay of several microseconds) due to extrinsic Ti-impurity centers. Moreover, the evolution of intrinsic visible bands during the material transformation was monitored. The relationship between structural parameters uniquely occurring in nanosized materials and the optical properties was investigated and tentatively modeled. The blue emissions at 2.5 and 2.9 eV are clearly related to defects lying at crystal boundaries, while an unprecedented emission at 2.1 eV enables, at relatively low calcination temperatures, the white luminescence of HfO2 under near-UV excitation.

High density powder phosphors are of great interest in technological fields like imaging and ionizing radiation detection. The powder form is of choice when the material can hardly be synthesized as bulk single crystal by conventional techniques. This is the case of hafnium oxides having a melting point above 2500 °C. Moreover nanoscale dimensions are an important requirement for fabricating nanocomposites, in nanomedicine, and for the realization of optical ceramics. In this last field materials with cubic structure are foreseen since their isotropic optical response allow the minimization of light scattering at grain interfaces. This work focuses on the synthesis, structural and optical investigation of HfO2 nanoparticles obtained by non-aqueous sol-gel route. In a first investigation, particular attention was paid to doping with europium and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol%, for either Lu3+or Eu3+ [1]. The spectroscopic features of Ti3+ impurities have been recently analyzed by room temperature radio- and photo-luminescence, time resolved luminescence and scintillation experiments. In addition, we have detected an intrinsic blue emission peaking at 2.5 eV and exhibiting a fast photoluminescence decay time of a few nanoseconds. This emission is due to the presence of surface defects; its intensity, as well as that of an additional band peaking at 2.1 eV, can be varied by thermal treatments that lead to surface modifications and variations of particle dimensions. For temperatures between 500 and 650 °C, tuning of the bands intensities induces a white emission under 3.5 eV excitation. The results demonstrate that the control of intrinsic defects is a potential route to design the optical activity of a material at the nanoscale. [1] A. Lauria et

FLARES (a Flexible scintillation Light Apparatus for Rare Event Searches) is a project for an innovative detector technology to be applied to rare event searches, and in particular to neutrinoless double beta decay experiments. Its novelty is the enhancement and optimization of the collection of the scintillation light emitted by ultra-pure crystals through the use of arrays of high performance silicon photodetectors cooled to 120 K. This would provide scintillation detectors with ∼1% level energy resolution, with the advantages of a technology offering relatively simple low cost mass scalability and powerful background reduction handles, as requested by future neutrinoless double beta decay experimental programs.

The radioluminescence (RL) spectra of three types of quartz have been compared to those obtained from wavelength resolved thermally stimulated luminescence (TSL) measurements. A detailed numerical deconvolution into Gaussian components allowed to identify which of the bands are involved in either types of luminescence processes. The blue "A band" at 2.51 eV was confirmed to dominate both RL and TSL spectra in samples exposed to prolonged irradiation. The UV emission of the 110°C TSL peak was found to be composite. Analogously to what previously reported for RL spectra, an annealing at 500°C for 10 min induced a strong enhancement of the "C band" at 3.42 eV. This effect was particularly evident in natural and pre-irradiated quartz. A second intense UV component, the "M band" at 3.7 eV, was found to contribute to both TSL and RL spectra of samples annealed at 1000°C for 10 min. A further broad UV emission seems to be involved only in RL emission but not in the TSL one.

TiO2 nanoparticles were supported on a new persistent luminescence (3ZnO:Ga2O3:2GeO2):Cr3 + material. The sample was characterized by means of X-ray powder diffraction, scanning electron microscopy and radioluminescence. The photoactivity was evaluated for the degradation of methylene blue (MB) in aqueous solution especially in the darkness. A MB photodegradation occurred also in the absence of an external illumination. In fact, the persistent luminescence material stores and provides the necessary photons to the TiO2 allowing the photocatalysis process even in the darkness.

The effectiveness and the mechanism of copper stain removal from stones by agar gels was systematically studied using marble laboratory specimens, stained and cleaned in well-controlled and reproducible conditions. The same cleaning procedure was also applied on the marble base of Napoleon's statue by A. Canova. The water release from agar gels to stones was investigated by capillarity absorption and unilateral Nuclear Magnetic Resonance. The cleaning by different agar gel formulations (pure and added with chemicals) was studied both on the stone substrate (optical microscopy and colour measurements) and in the gels (inductively coupled plasma-atomic emission spectrometry, electron paramagnetic resonance spectroscopy). Among the considered cleaning systems, the most effective ones for copper removal were agar gels 3% containing additives, with no significant difference among the used additives. However, agar gels with additives host copper in different ways: in gels added with ethylenediamine tetraacetic acid (EDTA), all copper centers are coordinated, while copper centers are also dispersed in water within gels added with ammonium citrate tribasic (TAC). The stain cleaning process of stones probably starts with the diffusion of water at the gel-stone interface, but it finds the driving force in the copper coordination.

Future research in High Energy Cosmic Ray Physics concerns fundamental questions on their origin, acceleration mechanism, and composition. Unambiguous measurements of the energy spectra and of the composition of cosmic rays at the "knee" region could provide some of the answers to the above questions. Only ground based observations, which rely on sophisticated models describing high energy interactions in the earth's atmosphere, have been possible so far due to the extremely low particle rates at these energies. A calorimeter based space experiment can provide not only flux measurements but also energy spectra and particle identification, especially when coupled to a dE/dx measuring detector, and thus overcome some of the limitations plaguing ground based experiments. For this to be possible very large acceptances are needed if enough statistic is to be collected in a reasonable time. This contrasts with the lightness and compactness requirements for space based experiments. A novel idea in calorimetry is discussed here which addresses these issues while limiting the mass and volume of the detector. In fact a small prototype is currently being built and tested with ions. In this paper the results obtained will be presented in light of the simulations performed.

Rare earths-doped silica optical fibers have shown promising results for ionizing radiation monitoring, thanks to their radio-luminescence (RL) properties. However, the use of these systems for accurate and precise dosimetric measurements in radiation fields above the Cerenkov energy threshold, like those employed in radiation therapy, is still challenging, since a spurious luminescence, namely the "stem effect" is also generated in the passive fiber portion exposed to radiation. The spurious signal mainly occurs in the UV-VIS region, therefore a dopant emitting in the near infrared may be suitable for an optical discrimination of the stem effect. In this work, the RL and dosimetric properties of Yb-doped silica optical fibers, produced by sol-gel technique, are studied, together with the methods and instruments to achieve an efficient optical detection of the Yb3+ emission, characterized by a sharp line at about 975 nm. The results demonstrate that the RL of Yb3+ 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.

Point defects in the host lattice of a scintillator material can trap carriers, slowing down their migration or even preventing their transfer to luminescent centers. Such competition schemes between defects and luminescent centers may explain also the hysteresis effect, which consists of a progressive enhancement of scintillation efficiency with accumulated dose. We propose a comparison between the scintillation hysteresis effect of Yb-doped sol-gel silica glasses in bulk and fiber forms, and we correlate them with traps monitored by wavelength-resolved thermally stimulated luminescence in both materials. The results demonstrate that the fiber-drawing process is responsible for modifications of the defectiveness of the glass network, with a change of the local distribution of the traps surrounding the luminescent center. The consequence of such modifications is the removal, in the fiber samples, of the thermally stimulated luminescence peak ascribed to traps closer to Yb ions and unstable at room temperature. We highlight that suitable postdensification thermal treatments can significantly modify the concentration and spatial distribution of defects around a luminescent center and can therefore be used as a tool for the engineering of scintillating glasses.

Modern applications of scintillator materials demand cutting-edge performances and require often a response speed in the nanosecond time scale. Slow light emission causing an "afterglow" is, therefore, of considerable concern in the development of fast scintillators. The mechanism of afterglow emission in mixed Ce-doped oxyorthosilicate scintillators is investigated by means of time-resolved scintillation, thermally stimulated luminescence (TSL), and radio-luminescence measurements. Various Ce-doped Lu2xGd2-2xSiO5 oxyorthosilicate crystals (with x ranging from 0 to1) and Lu1.8Y0.2SiO5 grown by the Czochralski technique are considered. The detailed TSL analysis reveals that thermally assisted tunneling recombination of electrons trapped by oxygen vacancies with holes trapped by Ce luminescence centers occurs for all compositions. The reduction of the afterglow intensity by adding gadolinium or yttrium into the host is accompanied by a lowering of the traps concentration, as deduced by the TSL intensity. Such lowering of the oxygen vacancy concentrations is found to be correlated with the decrease of the melting temperature induced by gadolinium or yttrium content increase, which governs the oxygen vapor pressure. The occurrence of a similar mechanism also in other scintillators and its influence on carrier trapping is discussed.

Future space experiments dedicated to the observation of high-energy gamma and cosmic rays will increasingly rely on a highly performing calorimetry apparatus, and their physics performance will be primarily determined by the geometrical dimensions and the energy resolution of the calorimeter deployed. Thus it is extremely important to optimize its geometrical acceptance, the granularity, and its absorption depth for the measurement of the particle energy with respect to the total mass of the apparatus which is the most important constraint for a space launch. The proposed design tries to satisfy these criteria while staying within a total mass budget of about 1.6 tons. Calocube is a homogeneous calorimeter instrumented with Cesium iodide (CsI) crystals, whose geometry is cubic and isotropic, so as to detect particles arriving from every direction in space, thus maximizing the acceptance; granularity is obtained by filling the cubic volume with small cubic CsI crystals. The total radiation length in any direction is more than adequate for optimal electromagnetic particle identification and energy measurement, whilst the interaction length is at least suficient to allow a precise reconstruction of hadronic showers. Optimal values for the size of the crystals and spacing among them have been studied. The design forms the basis of a three-year R&D activity which has been approved and financed by INFN. An overall description of the system, as well as results from preliminary tests on particle beams will be described.

The process of hole and electron localization in LuAG:Ce,Mg ceramics is studied by electron spin resonance (ESR) and thermally stimulated luminescence (TSL). Hole traps, which are created by UV irradiation, are detected in the form of O- centers. Mg-perturbed variants of O- centers are proposed to exist. The thermal stability of such defects is studied, proving that they are stable up to room temperature. The interaction between O- centers and shallow electron traps is studied by thermally stimulated luminescence (TSL) and phosphorescence experiments, which reveal the occurrence of an a-thermal tunneling process between trapped electrons and randomly distributed Ce centers. By correlating the TSL-derived trap parameters and temperature dependent ESR intensities, it is found that O- centers compete with Ce centers in free electron capture.

Optical ceramics are finding a strong technological interest in the field of laser and scintillation materials as an alternative to single crystals. The most favourable structural composition is the cubic one; in fact, due to the isotropy of the optical parameters occurring in this case, it is possible to obtain highly transparent bulk materials made of compacted micro - or nano - metric grains. Presently the mostly studied optical ceramics are rare-earth doped Y- and Lu- Aluminium garnets [1, and references therein]. In several cases sintering agents like Si, Mg, Sc, or La are also used. Indeed, it was found that their introduction causes a transparency improvement, accompanied, however, by a deterioration of the scintillation properties in terms of light yield and time decay. It was suggested that such ions, irrespective of their valence, introduce local disorder and cause the formation of point defects acting as traps and affecting the migration of charge carriers to the luminescence centres [1-3]. As a matter of fact, irrespective of sintering agents local disorder is inherently present in optical ceramics due to the existence of grain boundaries. Really, such ceramics are intriguing systems characterized by the simultaneous presence of relatively ordered regions within the grains, which constitute the major part of the material volume, and of defect-rich interface regions between grains. In these boundary regions segregation of rare-earth doping ions was also found to occur [4]. Thermally stimulated luminescence (TSL) experiments have been performed on Lu3Al5O12 (LuAG) ceramics doped with Ce3+ or Pr3+ in order to characterize defects in such materials and to compare the results with the defect properties in single crystals [1-3]. In this contribution, we focus on the information that can be obtained from such measurements specifically concerning the occurrence of local disorder, which causes a broadening of glow curves related to inhomogeneous broadening of def

Radiation induced sensitization in scintillator materials (also commonly called “bright burn” or “memory effect”) represents an issue for those applications, like medical imaging and real-time radioluminescence dosimetry, which strongly rely on high reproducibility and dose linearity of the luminescence output. This effect is caused by defects which act as traps for radiation-induced free carriers and compete with the recombination centres along the recombination path, thus lowering the luminescence efficiency of the scintillation materials. Considering that the competition between these two processes is driven by the capture cross sections and by the relative concentration of empty traps with respect to that of the recombination centres, the progressive trap filling during ionizing irradiation results in an increase in the radiative recombination probability and, thus, in an enhancement in the RL intensity. Despite such effect might have profound consequences on scintillator performance, it has rarely been studied and only few reports are present in the literature [1-3]. Indeed, the use of standard scintillators (like LSO, YAG, ...) may prove difficult for a more thorough investigation on this effect mainly because of the critical dependence on material reproducibility in term of traps which are related to uncontrolled impurities and defects.We recently proposed YPO4:Ce,Nd as a model material for such a study [4], since the main electronic trap is represented by Nd3+ ions [5] whose content can be easily selected during the sample synthesis. The obtained results clearly showed that RL efficiency increase is strongly dependent on the Nd content and on measurement temperature. On the basis of the experimental results, a model based on thermoluminescence trap filling and able to accurately describe the memory effect was proposed. In this communication, we extend our work on the memory effect performed on YPO4:Ce,Nd by considering two other ions (namelyPr andDy) in plac

Luminescent materials have found a wide variety of applications as phosphors for fluorescent lighting, display devices, X-ray monitoring and imaging, scintillators, and biomedical imaging. Indeed, the research in nanosciencehasbeen especially dedicated to the development of synthesis routes with the ability to synthetizenew material structures for industrial applications [1]. Fervent research in nanostructured materials has resulted in the development of novel synthetic methods to prepare pure and doped luminescent materials, and strategies to control the incorporation of dopant ions in nanoparticles. Hafnium oxide (HfO2) is considered as an attractive material because of its excellent physical and chemical properties, such as its high dielectric constant and insulating characteristics, which allow its application as a dielectric material with relatively high refractive index and wide band gap, as well in the field of optical coatings and next generation metal-oxide semiconductor devices. Moreover in recent investigations, nanometric hafnia when properly doped by rare earths (RE) ions has been also considered for optical applications [2]. Given the importance of HfO2 as host material for RE, its intrinsic optical response is also worth of investigation. In this work, we propose the study of the luminescent properties of undoped HfO2nanoparticles (NPs), achieved through a non-aqueous sol-gel process. The optical properties were studied by photo- and radio-luminescence considering the effect ofthe size and of the crystal phase. A broad composite emission was observed in the visible range, potentially correlated to intrinsic surface defects. A spectral analysis was performed, and the luminescence efficiency was compared to that of standard luminescent materials. Our studies reveal that HfO2 nanopowders may represent an interesting system in both phosphor technology and scintillation applications.

The recent progresses in the development and characterization of doped silica fiber optics for dosimetry applications in the modern radiation therapy, and for high energy physics experiments, are presented and discussed. In particular, the main purpose was the production of scintillating fiber optics with an emission spectrum which can be easily and efficiently distinguished from that of other spurious luminescent signals originated in the fiber optic material as consequence of the exposition to ionizing radiations (e.g. Cerenkov light and intrinsic fluorescence phenomena). In addition to the previously investigated dopant (Ce), other rare earth elements (Eu and Yb) were considered for the scintillating fiber optic development. The study of the luminescent and dosimetric properties of these new systems was carried out by using X and gamma rays of different energies and field sizes

A series of luminescent rare-earth ion-doped hexagonal II-type Gd oxycarbonate phosphors Gd2-xRExO2CO3 (RE = Eu3+, Yb3+, Dy3+) have been successfully synthesized by thermal decomposition of the corresponding mixed oxalates. The Yb3+ doped Gd-oxycarbonate has evidenced a high persistent luminescence in the NIR region, that is independent from the temperature and makes this materials particular attractive as optical probes for bioimaging

The role of charge carrier trapping in determining radioluminescence (RL) efficiency increase during prolonged irradiation of scintillators has been studied by using YPO4:Ce,Nd as a model material. The Nd3+ ions act as efficient electron traps minimizing the role of intrinsic defects. Different Nd contents were considered in order to point out the correlation between the trap concentration and the detected RL efficiency dose dependence. RL measurements as a function of temperature clarified the role of the trap thermal stability in determining the shape and the magnitude of such effect. We propose also a model based on trap filling which is able to describe accurately the complex processes which are involved. © 2014 American Chemical Society.

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. © 2014 AIP Publishing LLC.

During time-resolved optical stimulation experiments (TR-OSL), one uses short light pulses to separate the stimulation and emission of luminescence in time. Experimental TR-OSL results show that the luminescence lifetime in quartz of sedimentary origin is independent of annealing temperature below 500 C, but decreases monotonically thereafter. These results have been interpreted previously empirically on the basis of the existence of two separate luminescence centers LH and LL in quartz, each with its own distinct luminescence lifetime. Additional experimental evidence also supports the presence of a non-luminescent hole reservoir R, which plays a critical role in the predose effect in this material. This paper extends a recently published analytical model for thermal quenching in quartz, to include the two luminescence centers LH and LL, as well as the hole reservoir R. The new extended model involves localized electronic transitions between energy states within the two luminescence centers, and is described by a system of differential equations based on the Mott-Seitz mechanism of thermal quenching. It is shown that by using simplifying physical assumptions, one can obtain analytical solutions for the intensity of the light during a TR-OSL experiment carried out with previously annealed samples. These analytical expressions are found to be in good agreement with the numerical solutions of the equations. The results from the model are shown to be in quantitative agreement with published experimental data for commercially available quartz samples. Specifically the model describes the variation of the luminescence lifetimes with (a) annealing temperatures between room temperature and 900 C, and (b) with stimulation temperatures between 20 and 200 C. This paper also reports new radioluminescence (RL) measurements carried out using the same commercially available quartz samples. Gaussian deconvolution of the RL emission spectra was carried out using a total of seven em

Significant improvements have continuously been made in radiation therapy technologies, and therefore innovative detectors must also be developed to ensure the beam quality of these new irradiation systems and to allow in vivo dosimetry measurements. Optical fiber based radioluminescence (RL) dosimeters are a promising option for these purposes. They can enable real time dose measurement and their small size can be exploited in small radiation field dosimetry. A major difficulty involved in marketing these systems is the spurious luminescence, generally known as stem effect, that is intrinsically present in this type of detector. The possible mechanisms causing the stem effect during irradiation are fluorescence phenomena and especially Cerenkov light, produced in the undoped fiber portion. In this study we have faced the problem by making use of a spectral discrimination method exploiting the sharp 5D0-7F2 line emission of Eu3+ [1]. First, the incorporation of Eu3+ ions in sol-gel silica was investigated as a function of dopant concentration and synthesis parameters. Preliminary structural (TEM), vibrational (Raman, FTIR) and optical absorption studies [2, 3] have allowed to find the most suitable rare-earth (RE) concentrations and synthesis conditions for optimizing both RL efficiency and RE dispersion, avoiding the formation of aggregates. Indeed, clusters of few tens of nanometers were observed already for SiO2:3 mol% Eu3+. The 10 mol% doped sample contains also aggregates of much larger dimensions, whose diffraction patterns are in agreement with the presence of rare earth crystalline oxide silicates. Eu3+-doped fibers were realized by drawing cluster-free silica with 600 ppm doping level. The spectral emission of composite fibers made of a small portion (1 cm) of doped silica fiber coupled to a long (15 m) undoped fiber for remote signal transport has then been investigated under irradiation with photons and electrons of different energies, field sizes and ori

In the last decade, the interest in scintillating fiber optics for ionizing radiation monitoring is constantly increasing. Among the fields of possible applications of these sensors, radiation therapy represents a driving force for the research and development of new devices. In fact, the small dimensions of fiber optics based detectors, together with their realtime response, make these systems extremely promising both in quality assurance measurements of intensity modulated radiotherapy beams, and in in-vivo dosimetry. On the other hand, two specific aspects might represent limiting factors: (i) the stem effect, that is the spurious luminescence originating as a consequence of the irradiation of the light guide, and (ii) the memory effect, that is the radioluminescence sensitivity increase during prolonged exposition to ionizing radiation, typical of many scintillating materials. These two issues, representing the main challenges to face for the effective use of scintillating fiber as dosimeters in radiotherapy, were studied considering amorphous silica matrices prepared by sol-gel method and doped with europium. The origin of the stem effect was investigated by means of spectral measurements of the doped fibers irradiated with Xrays and electrons of different energies, field sizes and orientations. New approaches for removing the stem effect on the basis of the radioluminescent spectral analysis are presented and discussed. Furthermore, the causes and phenomenology of the memory effect are described, considering also the effect of dose accumulation with different dose rates and energies of ionizing radiation.