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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. © 2012 Elsevier Ltd.

The radioluminescence (RL) of synthetic quartzes (GEMMA Quartz & Crystal Company) has been measured at room temperature. Some samples were treated by electrodiffusion (sweeping) in order to change the concentrations of alkali ions, mainly Li + and Na +, which in quartz are known to be linked to Al ions, substitutional for Si ions. The RL emission spectra show evidence of a role of alkali ions in affecting some specific emissions. All the spectra could be analysed as composed of four bands in the blue and UV region. Specifically, the well known blue emission at around 470 nm was seen to be composed by two bands at 430 nm (2.86 eV) and at 485 nm (2.53 eV). Effects of irradiation, during the RL measurements, were clearly seen only in the Li swept in sample, namely an increase in the 485 nm band intensity and a decrease in the 430 nm band one. The previously reported UV emission was detected at 355 nm (3.44 eV) in all the samples, being the most intense band in the swept out sample. A further UV emission was detected at 315 nm (3.94 eV), more intense in untreated samples. Possible assignments of the detected emission bands are discussed in relation to the defects of quartz, specifically focusing on the Al centres that are most affected by sweeping procedures. © 2011 Elsevier B.V. All rights reserved.

The effect of X-ray irradiation and thermal treatments on the radio-luminescence emission spectrum of both a natural pegmatitic quartz and a synthetic one was investigated. All the emission spectra could be deconvolved into the same set of five Gaussian components. Among the identified RL bands, a blue emission at 2.53 eV (480 nm) is enhanced under X-ray irradiation. A strong correlation with the sensitization of the so called "110 degrees C" TSL peak (in our measurements seen at lower temperature due to the lower heating rate) was proved, suggesting that the recombination centers associated with the 2.53 eV band are produced under X-ray irradiation and are involved in both RL and TSL luminescence mechanisms. When each irradiation was followed by heating up to 500 degrees C a strong sensitization of the RL band emitting at 3.44 eV and of the 110 degrees C TSL peak were observed. A perfect correlation between the RL and TSL emissions suggests that the recombination centers involved in the RL and TSL emissions are the same

We improve a recently proposed approach for the evaluation of the thermal ionization barrier of the lanthanide excited states in luminescent materials by taking into account the effect of traps and their decay time temperature dependence. We present two distinct methods, and we apply them to the case of Lu2Si2O7:Pr. To this purpose, wavelength resolved thermally stimulated luminescence and photoluminescence time decay measurements extending up to the ms time scale have been performed. In the frame of the first method, the thermal ionization barrier of the Pr3+ 5d(1) excited state has been evaluated by studying the progressive filling of traps during illumination by ultraviolet light within the 4f-5d(1) absorption band of Pr-3+ at different temperatures. The thermal ionization barrier turned out to be 0.54 +/- 0.05 eV. In the second approach this parameter has been calculated by a numerical reconstruction of the temperature dependence of the 5d(1)-4f delayed recombination decay integral in two different time windows ([p53.3 mu s -10.3 ms] and [53.3 mu s -600 s]) with the sum of contributions from different traps whose parameters have been investigated by thermally stimulated luminescence (TSL). The results obtained are in agreement with those found using the trap-filling method. The advantages and limits of both approaches have been critically exposed, in order to discuss the possibility of their extensive employment for the determination of the ionization barrier of a rare earth ion excited-state level in an insulating host.

Undoped, Ce3+, Pr3+ and Eu3+ doped lutetium oxyfluoride submicrometre powders have been prepared by a simple coprecipitation procedure in water. The synthesized samples are Vernier single phases with a stoichiometry assigned to Lu10O9F12, as demonstrated by X-ray powder diffraction. The structural disorder of the host matrix significantly affects the optical emission spectra of the lanthanide doped samples as well as their vibrational spectra. The observed bandwidths of the FTIR spectrum and Raman scattering of the undoped sample are consistent with a very disordered nature of the host. From an analysis of the emission spectra of the Eu3+ doped sample it was found that different sites accommodating the lanthanide ions are present in the crystal structure. The Pr3+ and Ce3+ doped oxyfluoride samples show radioluminescence emission both in the UV and visible regions. The UV emission is due to lanthanide 4d-5f transitions, differently from the behavior observed for Ce3+ and Pr3+ doped Lu2O3, showing no UV emission. Considering the high mass density (close to 9 g cm(-3)), and the suitable location of rare earth ion electronic levels in the material band gap, as demonstrated by the observation of radiative emissions for all activators, the materials under investigation can be considered interesting candidates for scintillator or phosphor materials in the UV and visible regions.

We study defect states in Pr3+-doped Lu2Si2O7 crystal by wavelength resolved thermally stimulated luminescence both below and above room temperature. We identify the TSL peaks, analyze them by the initial rise technique and calculate the characteristic parameters of the corresponding traps. The role of tunnelling of charge carriers between traps and recombination centers up to RT is observed and discussed. The TSL spectra show that the charge carrier recombination predominantly occurs at Pr3+ centers. We also provide some comparison with the LPS:Ce3+ crystal prepared by the same method. (C) 2011 Elsevier B.V. All rights reserved.

Structural and optical properties of solgel silica based glassceramics doped with 0.1 mol% Ce and codoped with Gd at high concentrations, from 5 mol% up to 40 mol%, are investigated and compared to those of analogous samples doped only with Ce. Raman scattering, transmission electron microscopy, and x-ray diffraction reveal the formation of Gd apatite-like silicate (Gd 4.67O(SiO4)3) and of Gd pyrosilicate (Gd 2Si2O7) nanophases whose morphology and crystallinity depend on the Gd concentration and thermal treatments. Optical absorption measurements demonstrate the role of the densification atmosphere in modifying the charge state of Ce ions. The incorporation of Ce3 ions in the nanophases is put in evidence by photo- and radio-luminescence results

We study lutetium hafnate, Lu4Hf3O12, prepared by acetate and citrate combustion in the form of nanometric powders. Optical properties including X-ray excited luminescence, steady-state and time resolved photoluminescence as well as thermally stimulated luminescence are investigated for undoped as well as Eu3+ and Tb3+ doped samples. We identify recombination centers in the host matrix and we tentatively associate the principal emission with a radiative transition of the F + center. We also demonstrate that athermal tunneling of charge carriers between traps and recombination centers is the predominant mechanism of delayed radiative recombination following irradiation by ionizing radiation. © 2011 Elsevier B.V. All rights reserved.

Yttria-stabilized zirconia (ZrO2:Y3 +) single crystals (with 9.5mol% Y2O3) were irradiated with ions (from 1MeV He to 2.6GeV U). Electron paramagnetic resonance (EPR) data show that two kinds of colour centres (F+-type and T centres) are produced. Thermo-stimulated luminescence (TSL) data exhibit a quite strong peak at ∼ 500-550K in the glow curves of all irradiated samples regardless of the ion species and energy. Moreover, the 3D-TSL measurements reveal that this peak is correlated with a light emission at a wavelength of ∼ 620nm (i.e.photon energy ∼ 2eV). The TSL peak maximum temperatures are consistent with characteristic temperatures of about 500K of annealing stages of colour centres. However, the trap-depth energies (ranging between 0.7 and 1.4eV) deduced from the initial rise of partially cleaned TSL peaks, or from a rough approximation using Urbach's formula, are rather larger than the activation energies for defect recovery, ranging between 0.3 and 0.7eV, as deduced from the EPR data. The processes involved in TSL are discussed in relation to available photoluminescence and defect energy-level data. © 2011 IOP Publishing Ltd.

We employ a combination of first-principles calculations and optical characterization experiments to explain the mechanism by which Ga3+ doping prevents the trapping of free carriers due to shallow traps in RE 3Al5O12 garnet scintillators (where RE represents a 3+ rare-earth cation). Specifically, we confirm that Ga3 + doping does not reduce the defect concentration (defect engineering), but rather leads to shifts in the valence and conduction bands such that the energy level of shallow defects is no longer in the forbidden gap where electrons can be trapped (band-gap engineering).

The synthesis of rare-earth doped Lu4Hf3O 12 phosphor nanopowders was achieved through the combustion of metal-organic acetate-citrate amorphous gels. Their crystalline structure and morphology have been characterized by X-ray diffraction and electron microscopy. Under UV and X-ray excitation a bright luminescence of the Eu3+ and Tb3+ dopant ions has been monitored by photo-luminescence as well as by radio-luminescence measurements. We highlight the role of the formation of nanosized precursor gels as an intermediate stage in the synthesis of high-density rare-earth doped Lu4Hf3O12 luminescent nanopowders.

To better understand the scintillation mechanism in SrHfO3-based scintillators we investigate in detail their x-ray excited radioluminescence (RL) emissions. The Gaussian decomposition of the undoped SrHfO3 RL spectra manifests the presence of four emission bands peaking at 3.0, 4.0, 4.6, and 5.1 eV. Based on corresponding photoluminescence emission and excitation spectra we tentatively associate the observed bands with excitonic or defect-related emissions. When doped by Ce3+ or Pb2+ luminescent activators, the RL spectra feature two or three new bands, respectively. The temperature dependence of all RL spectra demonstrates a competition between activators and intrinsic or defect centers in carrier capture. Around room temperature the emission process is completely dominated by recombination at activator centers. In the case of Pb2+ activator we also study in detail the concentration dependence of the RL spectra below room temperature exhibiting an optimal value around 0.3 mol %.

Photo- and thermo-luminescence techniques are applied to several kinds of single crystal complex oxide scintillators to reveal tunnelling-driven radiative recombination processes. The tunnelling mechanism provides the physical ground to interpret the observed luminescence and scintillation characteristics which could not be explained by classical radiative recombination schemes

In the present work the effects produced by Eu3+ incorporation into sol-gel silica (doping level range: 0.001-10 mol%) are monitored by means of Fourier transform vibrational spectroscopy in the wave number range 200-3000 cm(-1). Complementary microreflectance, TEM, and Raman spectroscopy measurements are also performed. By increasing the Eu3+ concentration up to 3 mol%, the intrinsic absorption/reflectance bands related to vibrational modes of O-Si-O groups are gradually modified for what concerns the peak position and intensity, and absorption shoulders attributable to the Eu3+ doping appear. At 10 mol% sharp, new, Eu-related peaks grow at the expenses of the intrinsic absorptions. The results can be explained in terms of Eu-rich cluster formation, as also supported by Raman spectra analysis and TEM images. The cluster sizes increase by increasing the Eu3+ concentration. Their structure, in which tetrahedral (SiO4)(4-) groups are still present, remains amorphous for Eu3+ concentration up to 3 mol%, turning into a nearly ordered arrangement for the higher one. The spectral analysis in the regions of the weaker absorptions due to combination and overtone modes further supports the results and allows to associate the fundamental and overtone frequencies for two modes in Eu3+ 10 mol% doped silica. In the framework of the Morse anharmonic oscillator model, the related anharmonicity parameters and binding energies were calculated and found close to those reported for (SiO4)(4-) groups.

We present a systematic study of lead tungstate crystals doped with a small fraction of molybdenum, varying between 0.1% and 5%. These crystals were exposed to a beam of 50 GeV electrons and the signals were unraveled into scintillation and Cherenkov contributions, using the time structure of the signals and/or different types of transmission filters. These studies were carried out in view of the possible application of such crystals in dual-readout calorimeters. (C) 2010 Elsevier B.V. All rights reserved.

A numerous set of Pr-doped YAP single crystals was prepared using Czochralski and micro-pulling down methods. Crystals codoped by bi-, tri- and tetravalent ions were prepared by the latter method as well. The scintillation performance of all the prepared materials was evaluated using radioluminescence, photoelectron yield and scintillation decay measurements at room temperature. The influence of shallow traps was studied by means of thermoluminescence in the 10-350 K temperature range. Though the intrinsic scintillation efficiency of Pr-doped YAP is higher than that of YAP:Ce, enhanced delayed radiative recombination processes are found to be responsible for lower-than-expected photoelectron yield of the former system. The possibilities of further optimization of Pr-doped YAP scintillator are discussed. © 2010 IEEE.

Transmission electron microscopy, Raman scattering, Fourier transform infrared spectroscopy, and radio-luminescence are employed to investigate rare-earth (RE) incorporation and aggregate formation in silica glasses prepared by the Sol-Gel method and doped with Ce3+, or Tb3+, Gd3+, Yb3+ with concentrations up to several mol%. The results demonstrate that rare-earth aggregates with a mean diameter extending up to several tens of nanometers occur, further increasing their size after post-den-sification high temperature treatments. Rare-earth segregation causes a reduction of the OH content of glasses. Nanoclusters are amorphous, possibly close to a (RE)2SiO3 stoichiometry. Room temperature radio-luminescence measurements reveal that the emission spectra are dominated by RE3+ emissions and no bands due to silica matrix defects are detected. © 2010 IEEE.

LiCaAlF6 (LiCAF) crystals doped with two different ions (europium and lead) have been investigated as potential new dosimetric materials. The stability of thermally stimulated luminescence (TSL) glow peaks in LiCAF:Eu was evaluated by means of the initial rise technique. The decay times at room temperature of the traps related to the dosimetric glow peaks were found to range between 40 and 2 × 104 years confirming the good dosimetric characteristics of this crystal. The glow curve of LiCAF:Pb is dominated by a peak at approximately 300 °C emitting in the UV region ( 3P0,1-1S0 transition of Pb 2+) superimposed to a very broad structure at lower temperature (20-200 °C) featuring recombination at an intrinsic defect centre. The anomalous behavior of the low temperature structure during thermal cleaning procedures prevented any reliable numerical analysis of the TSL glow peak at 300 °C. © 2009 Elsevier Ltd. All rights reserved.

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 degrees C) display the highest light output. Moreover, Pb-doped SrHfO 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.

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. © 2010 IEEE.

We study defect states in undoped and Eu3+-doped Lu 3GaxAl5-xO12 (x = 0-5) garnet crystals by wavelength resolved thermally stimulated luminescence above room temperature. Eu3+ ions act not only as recombination centres but also as high temperature traps, as testified by the presence of a TSL peak at 450 °C correlated with Eu3+-doping. With increasing gallium content all glow peaks are shifted to lower temperatures. This trend is confirmed also for powder samples prepared by sol-gel technique. The observed low temperature shift of the glow peaks can be considered as a consequence of the band gap reduction following the increase of Ga3+ concentration. The comparison with the glow curve of a Ce3+-doped crystal is also shown. © 2010 Elsevier B.V. All rights reserved.

A radioluminescent (RL) dosimeter based on cerium-doped silica optical fibre was recently developed by means of the sol-gel and powder-in-tube techniques. The detector, already tested with both soft X-rays and more energetic photon beams used in conventional radiation therapy and in stereotactic radiosurgery, showed interesting and promising properties. A feasibility study for the use of the doped fibre in proton therapy is here presented. The measurements were performed at the proton therapy facility of the Paul Scherrer Institute (PSI) using a 138 MeV scanned proton pencil beam. The preliminary results showed a good sensitivity of the RL dosimeter to proton beams and a satisfactory reproducibility of the response (better than 0.5%) following repeated irradiations under the same experimental conditions. A linear dose response of the signal was observed in the investigated range (0.1-10 Gy) and, moreover, the stem effect proved to be negligible. The characteristic of the system to enable a real-time measurement of the dose rate was exploited for time-resolving different spot scanning sequences. Finally, the detector was used for assessing the depth dose curve in water: by comparing the curve obtained with the doped fibre with the corresponding one measured with a standard ionization chamber, a quenching effect in the order of 12% in the region of the Bragg peak was observed, as consequence of the decrease of the scintillation efficiency with increasing the Linear Energy Transfer (LET) of protons. © 2009 Elsevier Ltd. All rights reserved.

The trapping-recombination processes occurring in YAlO3 single crystals are investigated by wavelength-resolved thermally stimulated luminescence (TSL) studies from 10 to 300 K after x-ray irradiation at 10 K. Undoped crystals and crystals doped with rare earth ions are studied. The results obtained on undoped, Yb3+ -, Eu3+ -, and Tm3+ -doped samples indicate the existence of seven glow peaks due to intrinsic hole traps. Three of them (at 154, 190, and 232 K) are related to different variants of O centers, as demonstrated by the correspondence between the thermal stabilities of such centers detected by electron paramagnetic resonance and the glow peak temperatures. From the analysis of the TSL emission spectra it is found that rare earth ions, after capturing electrons during irradiation, play the role of recombination centers. The thermal depths and the room-temperature lifetimes of the traps are also evaluated. After doping with rare earth ions which are expected to act as hole traps such as Ce3+, Pr3+, and Tb3+ only one main peak is observed, preceded by a nearly temperature-independent emission which is completely suppressed at temperatures higher than the glow peak temperature. For each particular dopant the peak coincides with one of those observed in the undoped crystal while the TSL spectral emission is characteristic of the rare earth ion dopant. To interpret such results we suggest the existence of defect complexes, involving intrinsic defects coupled to Ce3+, Pr3+, and Tb3+ rare earth ions, in which carriers can be transferred from intrinsic levels to the rare earth ion levels, where the radiative recombination occurs. © 2009 The American Physical Society.

The effect of sintering atmosphere on the optical and structural properties of Cerium doped sol-gel silica was investigated. Two sets of xerogels with Ce concentration from 0 to 10 mol% were prepared and densified in different conditions. The effect of a post-densification rapid thermal treatment was also considered. Optical absorption measurements evidenced that in oxidizing conditions Cerium is preferably incorporated inside the silica matrix as Ce4+ while the trivalent state is favoured by reducing conditions. Transmission electron microscopy images show rare-earth clusters formation whose nature was investigated by means of Raman, EDS and microdiffraction measurements. In order to evaluate the efficiency of the glasses as scintillating materials radio-luminescence measurements were carried out. A numerical fit of RL spectra showed the presence of two components peaking at 2.7 and 3.1 eV. After RTT, the relative intensity of the 3.1 eV component increases with Ce concentration. © 2009 Elsevier B.V. All rights reserved.

An investigation of carrier trapping and recombination processes in CdWO4 crystals undoped and Li doped has been performed by wavelength-resolved thermally stimulated luminescence (TSL) studies following x-ray irradiation at 10 K. Particular focus has been paid to the temperature region from 10 to 100 K where as many as five TSL peaks were detected, with trap depths from 0.07 up to 0.19 eV. Two of them (at 61 and at 75 K) could be ascribed to the thermal detrapping of self-trapped holes (STH) and their subsequent radiative recombination with electrons localized at intrinsic defect sites. This ascription derives from the strong similarity of their energies and frequency factors (E=0.07eV and s= 104 s-1, E=0.08eV and s= 104 s-1) with those of recently studied STH paramagnetic defects. The TSL emission spectrum features both the intrinsic emission at 2.5 eV probably originating from the (WO6) 6- group and a further band at 1.9 eV previously ascribed to a transition within a (WO6) 6- group lacking of an oxygen ion. Our findings allow a detailed discussion on the trapping-recombination processes in CdWO4, also in comparison with those occurring in another tungstate like PbWO4. Moreover, the possible role of the detected traps in the scintillation performance of the crystal is discussed. © 2009 The American Physical Society.

Synthetic crystalline quartz, with known concentrations of Al and alkali ions was used in this study. The wavelength-resolved OSL spectra were measured after different periods of optical stimulation, and more than one emission band were detected. A composite peak centred at 380 nm is seen; this is similar to the emission band for the 110 °C TL peak, that has been associated with the [AlO4]° recombination centres. A direct correspondence between OSL signal intensity and the alkali ion concentration was observed; the signal intensity in bulk crystalline "swept out" quartz, i.e. quartz submitted to electro-diffusion, was found to be much lower than that from the 'unswept' quartz. These data suggest that alkali ions play an important role in the OSL phenomenon. Based on the data presented here and the existing TL studies it is inferred that OSL and the 110 °C and 325 °C TL peaks share a common recombination centre. This emission is assigned to electron recombination at Al centres with a trapped hole, [AlO4]°. A preliminary phenomenological model of TL and OSL is proposed, which is based on a spatial association between the OSL and the 110 °C TL trap. © 2009 Elsevier Ltd. All rights reserved.

We present an investigation of defects acting as electron traps in Lu 2SiO5 (LSO) and LuxY2-xSiO 5 (LYSO) performed by wavelength-resolved thermally stimulated luminescence (TSL) measurements from 20 to 400°C after room-temperature (RT) x-ray irradiation. Single crystals doped with several rare-earth ions such as Ce, Tb, Tm, and Sm were considered. A comparison between TSL and RT radio-luminescence (RL) emission spectra is also presented. The glow curves for both LSO and LYSO are similar, showing a series of TSL peaks at 78, 135, 181, and 236°C. In addition, a further peak at about 300°C is observed only in LYSO. Our results confirm the role of oxygen vacancies as electron traps in the material; the presence of several glow peaks with a unique trap depth (0.99eV±0.07 eV) for the 78, 135, 181, and 236°C peaks is explained by suggesting that electrons stored in oxygen vacancies recombine through a thermally assisted tunneling mechanism with holes localized at Ce3+ or Tb3+ centers residing on Lu sites at different crystallographic distances from the traps. This model is supported by the very good correlation among O-Lu distances in the monoclinic C2/c structure of LSO and LYSO and the frequency factors of the traps containing the transmission coefficients of the potential barriers between traps and centers, evaluated in the framework of the thermally assisted tunneling process. Tm and Sm ions do not act as TSL recombination centers possibly due to their tendency to trap electrons during irradiation with ionizing radiation. © 2008 The American Physical Society.

Participation of shallow and deep traps in the processes of energy transfer and capture is studied by means of time- resolved emission spectroscopy and thermoluminescence in several groups of Ce3+ and Pr3+-doped complex oxide single crystal scintillators. Tunnelling-driven recombination processes are distinguished in all the examined materials: closely spaced electron and hole traps give rise to the t-1 phosphorescence decays at low temperatures in the Ce-doped aluminum garnets and perovskites, while thermally assisted tunneling process is proposed to explain the temperature independent trap depth in glow curve peaks within 50-250 C in Ce-doped lutetium orthosilicates.

The aim of this work is to investigate the influence of shallow traps on scintillating properties of YAlO3 : 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 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. © 2008 IEEE.

A thorough study was performed on Gd-doped sol-gel silica glasses, in the concentration range 0-8 mol% Gd. The analyses were carried out as a function of Gd content, before and after a post-densification thermal treatment. Different results concerning optical, vibrational, magnetic, and structural features were gathered in correlated experiments. The presence of Gd-rich nanoclusters was revealed. The size of nanoclusters increases by increasing the dopant concentration and by performing a rapid thermal treatment (RTT) at 1800 °C in air, which causes also a remarkable intensity increase of the 6P7/2 →8S7/2 radioluminescence transition of Gd3+. Nanoclusters are amorphous, possibly close to a Gd2SiO5 stoichiometry as suggested by fast Fourier transform infrared spectroscopy (FTIR). FTIR studies revealed also the presence of Gd-dimers interacting with OH- groups. Moreover, the presence of isolated Gd3+ ions was detected by electron paramagnetic resonance investigations. Based on the results obtained with different techniques, the Gd-incorporation in silica glass host and the resulting optical properties are discussed. © 2008 Elsevier B.V. All rights reserved.

Photon beams produced by a cobalt-60 Unit and a 6 MV linear accelerator equipped with stereotactic collimators were used to investigate some dosimetric properties of a radioluminescent dosimeter based on a Ce-doped optical fibre. The stability of the signal with increasing the irradiation time, enabled a reliable and real-time measurement of the dose rate. The methods, recently developed, of optical coupling, light collection and signal processing allowed to achieve a satisfactory signal to noise ratio, a good reproducibility and a linear dose-response. The punctual dimension of the doped fibre diameter was exploited in the characterization of stereotactic fields, providing results in agreement with those obtained using a micro-ionization chamber. © 2008 Elsevier Ltd. All rights reserved.

PbWO4 single crystals with praseodymium doping in a wide concentration range (0.1-5 at % in the melt) were grown by Czochralski method. Absorption, luminescence, and scintillation characteristics were measured at room temperature. Similar to other trivalent dopants, heavy Pr3+ doping on one hand suppresses intrinsic host scintillation. On the other hand though, in the scintillation decay it introduces components with characteristic decay times within 500-2000 ns based on Pr3+ 4f-4f emission lines in the green-red part of the spectra. We discuss the suitability of such material for dual scintillation/Cherenkov light detector. © 2008 American Institute of Physics.

In this study we investigate the role of traps on radio- and photo-luminescence properties of terbium doped silica. The investigation is motivated by the promising characteristics of rare-earth doped silica obtained by the sol-gel technique as scintillating material. We focus on those phenomena that can be responsible for problematic properties such as the increase of radio-luminescence sensitivity following repeated irradiations. A set of terbium doped silica with different terbium concentrations (0.03 mo1%, 0.1 mo1% and 10 mo1%) prepared by the sol-gel technique and densified at 1050 °C in oxidizing atmosphere has been considered. The effect of a post-densification rapid thermal treatment on the RL and PL properties has also been investigated. This treatment improved the scintillation characteristics of the samples reducing their RL instability under prolonged irradiation.

Point defects and impurities play a major role in optical properties of scintillators, as they can be at the origin of afterglow emission, which are detrimental for the applications. Spectrally-resolved thermally stimulated luminescence (TSL) is used here to study defects possibly affecting scintillation properties of LaCl3:Ce and LaBr3:Ce samples grown by Saint-Gobain Crystals & Detectors. In the case of LaCl 3:Ce, after X-ray irradiation two major glow peaks with complex structures are detected at 23 K and 63 K (when measured at a heating rate of 0.1 K/s). A more composite structure of the TSL pattern of LaBr3:Ce is observed. Possible explanations and implications of these findings are discussed.

Phosphorescence emitted by a new dosimetric system based on a SiO2 optical fibre doped with Ce3+ ions was investigated. The defects in the matrix that, acting as electron traps, originate the phosphorescence signal were studied by means of thermally stimulated luminescence in the temperature interval 313-533 K. A continuous trap distribution with activation energies extending from 0.8 to 1.5 eV was observed. On the basis of these findings, the temperature dependence of the shape of isothermal phosphorescence decay was analysed and the corresponding spectrum was compared with that of radioluminescence.

Oxygen plasmas, commonly used in typical C-MOS process flow, cause silicon oxide structure to be significantly modified: as a consequence wet processes, that are sensitive to oxide defectivity, need to be retargeted. In this paper structure modifications, induced in boron implanted SiO2 by RF and TCP plasma have been studied by thermally stimulated luminescence, charging measurements and Electron Paramagnetic Resonance (EPR). Different kind and quantity of point defects have been identified by thermally stimulated luminescence technique as a function of plasma generator. These results match with EPR analysis, charging measurements and HF etches rate profile. © The Electrochemical Society.

A set of terbium-doped silicate glasses densified up to 1050 °C was prepared by the sol-gel method. A broad range of dopant concentrations (0.001-10 mol%) was considered together with an undoped sample as a reference. The effects of a high-temperature (1600-1800 °C) post-densification rapid thermal treatment (RTT) on the luminescence properties of the samples were investigated. RTT enhances the scintillating efficiency of the samples increasing the radio-luminescence intensity up to two orders of magnitude. The relevant effects induced by RTT on radio- and photo-luminescence spectra (RL, PL) and on PL decay curves indicate the occurrence of modifications of the surroundings of Tb3 + luminescence centres. © 2007 Elsevier Ltd. All rights reserved.

Optical absorption, luminescence, and scintillation characteristics of Lu3 Al5 O12: 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. Lu3 Al5 O12: 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 Y3 Al5 O12: Ce, the optical ceramics may therefore become competitive to the Lu3 Al5 O12: Ce single crystals, if trapping phenomena at other defects can be further reduced. © 2007 American Institute of Physics.

The optical properties of Yb-doped sol-gel silica glasses were studied by optical absorption and radio-luminescence (RL) measurements, that revealed the typical absorption and emission pattern of Yb3+ ions. Moreover, RL bands in the 1.5-3.5 eV interval were also observed, and related to defects of the silica matrix. The RL intensity temperature dependence, investigated in the 10-320 K interval, evidenced the presence of the SiO2 self-trapped exciton emission at 2.2 eV, whose intensity was rapidly quenched by temperature increasing. At variance, the Yb3+ emission intensity increased markedly by temperature increasing. This phenomenon is interpreted by considering a competitive role of point defects in free carrier trapping, evidenced by parallel wavelength resolved thermally stimulated luminescence measurements. © 2007 Elsevier B.V. All rights reserved.