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International audience; The carrier trapping and recombination mechanisms occurring in Ce-doped silica fibers, produced by a sol-gel technique, are investigated by combining temperature-dependent steady-state X-ray-excited luminescence, wavelength- and time-resolved scintillation measurements, and wavelength-resolved thermally stimulated luminescence, focusing especially on the temperature range from 10 to 320 K. The scintillation decay features a decay time of the order of tens of nanoseconds, characteristic of the parity- and spin-allowed 5d-4f radiative transition of Ce3+ ions. In addition, a slow and complex decay contribution in the microsecond timescale is detected. We interpret these features as due to the radiative recombination at Ce centers of carriers freed from a continuous distribution of trapping sites in the forbidden gap as well as to the occurrence of an athermal tunneling recombination process between traps and Ce3+ ions. This interpretation is reinforced by good agreement between independent evaluations of trap depths and lifetimes obtained by both the numerical analysis of scintillation time decays and thermally stimulated luminescence experiments.

The influence of fiber drawing on mechanical and vibrational properties of RE-doped sol-gel silica is disclosed by a comparison of bulk silica, before and after the melting process, and fibers. The mechanical characterization is carried out by nanoindentation technique: hardness and elastic modulus are found to be consistent with those of Corning 7980 reference glass, and related to the elasto-plastic behavior of the glassy material. Our results evidence an increase of the resistance of fibers to fracture under an applied load, ascribed to drawing-induced residual stresses. Their impact on sol-gel silica mechanical properties is further disclosed by complementary vibrational characterization by Raman and FTIR spectroscopies, confirming the occurrence of a modification of the structural features after the drawing process and of residual stresses in the fibers. The overall results highlight the role of the fiber drawing in improving the glass mechanical properties, causing a slight rearrangement of the silica structure.

Few species of reptiles are known to establish stable social structures and among these, chelonians provided scarce and conflicting results. Moreover, studies on turtles are usually performed on adult individuals. In this study, we checked whether and when hatchlings of the European Pond Turtle (Emys orbicularis galloitalica) established stable hierarchical structures in their first year of life, whether hierarchies were stable in time and how steady they were. We also verified whether social ranks were associated to the individuals&rsquo, size. We observed dyadic interactions daily within three small groups of turtles reared in a controlled environment for seven months. After two months, the hatchlings started to interact and progressively established stable hierarchical structures. However, the effectiveness of the three types of observed aggressive behaviors in reversing social ranks was low and the resulting hierarchies were flat. We did not find a significant effect of the turtles&rsquo, size on their interactions&rsquo, outcome and hierarchy structure. Our results provide clear evidence of the development and the characteristics of social behaviors in young reptiles in captivity. This study could be a starting point for investigating social structures in wild populations.

A beam profiler called the Universal Beam Monitor (UniBEaM) has been developed by D-Pace Inc. (Canada) and the Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics, University of Bern (Switzerland). The device is based on passing 100 to 600 micron cerium-doped optical fibers through a particle beam. Visible scintillation light from the sensor fibers is transmitted over distances of tens of meters to the light sensors with minimal signal loss and no susceptibility to electromagnetic fields. The probe has an insertion length of only 70 mm. The software plots the beam intensity distribution in the horizontal and vertical planes, and calculates the beam location and integrated profile area, which correlates well with total beam current. UniBEaM has a large dynamic range, operating with beam currents of ∼pA to mA, and a large range of particle kinetic energies of ∼keV to GeV, depending on the absorbed power density. Test data are presented for H - beams at 25keV for 500 μA, and H + beams at 18MeV for 50pA to 10 μA. Maximum absorbed power density of the optical fiber before thermal damage is discussed in relation to dE/dx energy deposition as a function of particle type and kinetic energy. UniBEaM is well suited for a wide variety of beamlines including discovery science applications, radio-pharmaceutical production, hadron therapy, industrial ion beam applications including ion implantation, industrial electron beams, and ion source testing.

The results of irradiation tests on Ce-doped sol-gel silica using X- and g-rays up to 10 kGy are reported, in order to investigate the radiation hardness of this material for high energy physics applications. Sol-gel silica fibers with Ce concentrations of 0.0125 mol% and 0.05 mol% are characterized by means of optical absorption and attenuation length measurements before and after irradiation. The two different techniques give comparable results, evidencing the formation of a main broad radiation-induced absorption band, peaking at about 2.2 eV, related to radiation-induced color centers. The results are compared with those obtained on bulk silica. This study reveals that an improvement of the radiation hardness of Ce-doped silica fibers can be achieved by reducing Ce content inside the fiber core, paving the way for further material development.

Scintillating optical fibres have shown interesting results for ionizing radiation monitoring. Since they may enable a remote, punctual and real-time dose assessment, their application in medical dosimetry is very promising. This work aims to summarize some recent progresses in the development and characterization of rare-earth doped silica optical fibres. The radioluminescent and dosimetric properties of Ce, Eu and Yb-doped fibres are presented and the advantages and challenges in the use of these sensors for radiation therapy dosimetry are discussed. For such application, an effective approach to deal with the stem effect, i.e. the spurious luminescent signal originated in the light guide as a consequence of its exposition to ionizing radiations (i.e. Cerenkov light and intrinsic fluorescence) must be considered. The stem effect mainly occurs in the UV-VIS region. We demonstrated that the use of a dopant emitting in the near infrared, like Yb, is suitable for an optical discrimination of the dosimetric signal. Indeed, through a characterization of the dosimetric properties of Yb-doped fibres in conjunction with an optical filter and an avalanche detector, we proved that the drawback due to the stem effect does not impair the system response even in the most challenging irradiation geometries, attesting to the robustness of the device in complex dosimetric scenarios.

Silica fibres doped with small (< 1 mol%) concentrations of gadolinium ions have been fabricated and tested in a 1T magnetic field showing a Faraday rotation two orders of magnitude larger than that reported in conventional telecom fibres. This is the largest Faraday rotation ever reported in low-loss optical fibers and could pave the way for a new class of optical isolators.

Enhancement of photoluminescence (PL) signal from Gd3+-doped silica glass densified by rapid thermal treatment (RTT) in the ultraviolet (UV) is investigated. Significant decrease of the loss covering the UV band is observed. The strong emission detected at 314 nm is assigned to the 6P7/2 to 8S7/2 transition under excitation of 6DJ, 6IJ, and 6PJ energy levels of the Gd3+.

Photoluminescence (PL) of Gd-doped silica in the ultraviolet (UV) is investigated. The strong emission detected at 314 nm is assigned to the 6P7/2 to 8S7/2 transition under excitation of 6DJ, 6IJ, and 6PJ energy levels of the Gd3+. After glass densified by rapid thermal treatment (RTT), significant enhanced luminescence and decreased loss covering the UV band are observed.

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.

The near-infrared radioluminescence and dosimetric properties of Yb-doped silica optical fibers, coupled with an optical detector prototype based on an avalanche photo-diode, were studied by irradiating the fibers with clinical beams generated by a Varian Trilogy accelerator. The performances of the system in standard and small field sizes have been also investigated comparing the output factor, percent depth dose and off axis ratio measurements of the prototypal dosimetric system with other commercial sensors. The results demonstrated that the drawback due to the stem effect in Yb-doped silica optical fibers can be managed in a simple but effective way by optical filtering. These features, together with the accuracy and precision achieved by Ybdoped fibers in relative dose assessments make the device promising for in-vivo dosimetry studies in radiation therapy.

Gd-doped silica and phosphosilicate fibers were pulled from preforms fabricated using the rod-in-tube technique and the solution doping technique, respectively. Ultraviolet (UV)-B luminescence from trivalent Gd at around 312 nm given by transition from first excited state to ground state were observed under deep UV excitations.

Optical fiber lasers operating in the near infrared (IR) and visible spectral regions have relied on the spectroscopic properties of rare earth ions such as Yb3+, Er3+, Tm3+, Nd3+ and Sm3+. Here, we investigate Gd3+ doping in phosphosilicate and pure silica fibers using solution doping and sol-gel techniques respectively for potential applications in the ultraviolet (UV). Photoluminescence spectra for optical fiber bundles and fiber preforms were recorded and compared. Emissions at 312 nm (phosphosilicate) and 314 nm (pure silica) were observed when pumping to the Gd3+ 6DJ, 6IJ, and 6PJ = 5/2, 3/2 energy levels. Oxygen deficient center was observed in solution doping sample with a wide absorption band centered at around 248 nm not affecting pumping to 6IJ states.

A beam monitoring detection technique based on silica fibers has been developed by AEC-LHEP. The light signal produced in a doped silica fiber crossing the beam is collected to measure the beam profile. Two types of detectors have been constructed and tested. The first one operates in vacuum and was tested at the 18 MeV medical proton cyclotron at the University Hospital in Bern. It is able to measure currents form a few pA to 20 µA. It can be employed to optimize the production of radioisotopes, in particular using solid targets. The second one operates in air and was tested with high-energy pion and proton beams at the CERF facility at CERN. This paper reports on both detectors with focus on the most recent results obtained with the second detector.

UV light has been generated in optical fibers using nonlinear optics (harmonic generation) and rare earth doping with Gd3+ Asia Communications and Photonics Conferene (ACP)

Photoluminescence (PL) of Gd-doped silica in the ultraviolet (UV) is investigated. The efficient emission detected at 314 nm is due to the 6P 7/2 to 8S 7/2 transition of a 4f electron of the Gd3+ ion.

Fluorinated silica glasses with improved vacuum ultraviolet (VUV) transmittance have been synthesized following a sol-gel route starting from fluorinated alkoxide precursors. Matrix dehydration and fluorination have been investigated by Raman, IR, and refractive index measurements. The results show that, during the densification step, the residual hydroxyl and fluorine content can be controlled by governing the kinetic equilibrium between matrix collapse and fluorine evolution. This highlights the pivotal role of in situ reactions of fluorine-containing molecular precursors in the networking mechanism of a sol-gel material after thermal activation. Superior VUV transmittance and radiation hardness with respect to pure commercial silica and undoped sol-gel silica have been confirmed by synchrotron light absorption measurements before and after X-ray exposure. These properties make the material very attractive for applications in VUV photolithography technologies and optical fibers, especially for use in environments with a high level of ionizing radiation, such as spacecrafts and nuclear power plants.

Structural and optical properties of sol–gel 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 (Gd4.67O(SiO4)3) and of Gd pyrosilicate (Gd2Si2O7) 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.

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 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.

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.

Elemental Ge nanophases are obtained in silica starting from a sol-gel synthesis. The process comprises the preparation of silica xerogel doped by Ge(IV), substituting for Si(IV) in the oxide network, followed by reduction and phase separation during the sintering process by reaction with H-2 or CO. X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy show that reactions with H-2 give rise in the porous silica network to nanometer-sized crystallization of elemental cubic germanium. (c) 2007 Elsevier Ltd. All rights reserved.

We show here what kind of modification of the interphase morphology of SnO2 nanoparticles in silica (average nanocrystal radius, \(\hat{r}\approx 4\,\hbox{nm}\) in undoped material; \(\hat{r}\,\approx\,2\,\hbox{nm}\) in erbium doped material) brings to the passivation of interfacial defects. Surface states, which may preclude the exploitation of UV excitonic emission, are reduced after doping by rare earth ions. We demonstrate, by means of transmission-electron-microscopy and small-angle-neutron-scattering data, that a smooth interphase with a non negligible thickness takes the place of the fractal and discontinuous boundary observed in undoped material.

We present a study of the optical properties of Gd-doped sol-gel silica glasses densified at different temperatures (from 450 up to 1050 °C) by means of optical absorption (OA) and radio luminescence (RL). The effect of a post-densification rapid thermal treatment (RTT) at approximately 1800 °C is also considered. Room temperature OA and RL measurements have revealed a slight low-energy shift of Gd3+ absorption/emission lines by densification temperature increasing accompanied by a parallel increase of Gd3+ RL intensities, especially strong after RTT. These effects are interpreted on the basis of structural modifications of the silica matrix and of the removal of non-radiative channels competing with Gd3+ emission. Moreover, RL spectra of fully densified samples display high-energy shoulders on the 6P7/2-8S Gd3+ emission possibly related to crystal field splitting of the 6P7/2 state. This interpretation is supported by the temperature dependence of RL spectra, investigated in the 10-320 K temperature interval: an increase of the intensity of high-energy components vs. temperature has been observed, which can be interpreted as due to thermally assisted excitation of electrons belonging to the lower 6P7/2 state to higher crystal field states and their subsequent radiative recombination. © 2006 Elsevier B.V. All rights reserved.

The effects of room temperature γ-ray irradiation up to a dose of ∼1300 kGy are investigated by Electron paramagnetic resonance (EPR) measurements in amorphous silicon dioxide (a-SiO2) produced by a sol-gel synthesis method that introduces O{triple bond, long}Si{single bond}Si{triple bond, long}O oxygen deficiency. We have found that exposure to radiation generates the Eγ′ center with the same spectral features found in high purity commercial a-SiO2. The maximum concentration of defects induced in this sol-gel material indicates that its resistance to radiation is comparable to that of synthetic fused a-SiO2. The concentration of Eγ′ center increases with irradiation, featuring a sublinear dose dependence up to the highest investigated dose and showing no saturation effects. This defect generation process suggests that the chemically induced precursor influences the mechanisms of Eγ′ center generation. © 2007 Elsevier B.V. All rights reserved.

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.

Radiation-induced spectral modifications of the 5 eV excited photoluminescence (PL) of oxygen vacancies have been found in a nanostructured silica-based material. This system, made up of SnO2 nanocrystals embedded in amorphous SiO2, is generated by nano-clustering in oversaturated Sn-doped silica produced by sol-gel method. Treatment in oxygen-poor atmosphere introduces oxygen deficiency in the glassy host and a photo-reactive SnO-like interphase at the SnO2 nanocrystal surface. PL measurements initially show native PL activity at 2.7 eV excited at 5 eV, ascribable to oxygen vacancies in intrinsic two-fold coordinated Si sites. Prolonged UV irradiation at 4.7 eV (fourth harmonic of Nd-YAG pulsed laser) gives rise to extrinsic PL activity at 3.1 eV, ascribable to Sn-variant of oxygen vacancy. The results suggest that the UV irradiation causes a progressive release of Sn from the nanophase surface to the glassy network in oxygen vacancy sites. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

International audience; 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.

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.

We investigate the effects of erbium doping on SnO(2) nanoclustering in Sn-doped silica. Vibrational spectroscopy data from Raman and infrared absorption measurements show nanostructuring effects on the SnO(2) nanophase. Ultraviolet absorption spectra evidence a gap shift ascribable to size-dependent quantum confinement, also suggesting a role of erbium doping in determining cluster sizes and the amount of localized states on the nanophase boundary. Transmission electron microscopy confirms and details the spectroscopic data. As a result of these measurements, we find that the nanocrystal size distribution becomes narrower, increasing the erbium concentration, while the density of localized states at the nanocrystal surface decreases. The distribution of erbium ions among the possible environments is then examined through simultaneous spectroscopy of luminescence excited by nanocrystal-to-erbium energy transfer and the absorption of nanocrystal luminescence by erbium ions. This analysis shows that erbium behaves as an extrinsic nucleation centre of the SnO(2) nanophase at low doping levels, whereas at high concentrations it modifies the matrix, hindering the growth of SnO(2) crystals and passivating the interface.

A feasibility study for the use of a Ce3+-doped optical fibre as a radio luminescent dosimeter in radiotherapy was carried out. The prototype showed a satisfactory reproducibility (1.7%) and a good linearity over a clinically relevant dose range (from few cGy to approximately 10 Gy). Moreover, the device enabled a reliable evaluation of the absorbed dose, independently of the dose rate and of the orientation of the incoming radiation. A slight energy dependence of the response was observed when the system was irradiated with electron beams of different energies. The results indicate that the employment of this new system might be very promising both for quality control measurements and "in vivo" dosimetry. Some improvements are nevertheless still required in order to allow a real-time evaluation of the Cherenkov radiation produced by the irradiated portion of the passive optical fibre, which influences some of the dosimetric properties of the system. (c) 2006 Elsevier B.V. All rights reserved.

Thermal poling has been investigated in silica-based glasses prepared by the sol-gel method. Samples with different OH-content (from 40 ppm to few 10(3) ppm), doping (oxygen-vacancies, substitutional Sn, SnO2 clusters) and post-synthesis treatment (X-ray irradiation) have been heated in vacuum at 280 degrees C with an applied voltage of 4 kV. Second-order non-linearity has been observed after poling, with chi((2)) of the order of 0.1 pm/V. The comparison among samples suggests that OH-content is not the only factor responsible for the observed non-linearity. (C) 2005 Elsevier Ltd. All rights reserved.

High-resolution soft X-ray spectra of H-like and He-like ions were produced from laser irradiated silicon and aluminum targets. Plasma size was about 100 μm. X-ray spectra were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the inter combination lines of He-like ions, with the results of model calculations. Such comparison gave average values of the electron density N e=(1−1.9)×1021 cm−3 and the electron temperature T e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. According to our estimations, more than 1012 photons were produced within the resonance line spectral width and in the solid angle 2π steredian during the total decay period.

We report an experimental study on the temperature dependence, in the range 18-300 K, of the decay kinetics of the emission at 4.1 eV from the first excited electronic state of oxygen deficient centers in a 2000 ppm Sn-doped sol-gel silica. At low temperature, this luminescence decays exponentially with a lifetime of 8.4 ns, whereas, on increasing the temperature, the time decay decreases and cannot be fitted with an exponential function. These results are expected if there is a competition between the radiative and the thermally activated intersystem-crossing decay channels toward the associated triplet state. The comparison with previous data in pure oxygen-deficient and Ge-doped silica gives new insight on the effect of the host-matrix dynamics on the electronic properties of this type of point defect. © 2005 Elsevier B.V. All rights reserved.

Silica glasses containing SnO 2 nanocrystals and Er 3 + ions were prepared by the sol-gel route and proper annealing treatments. A few samples were prepared with fluorinated Si precursors. Er 3 + transitions from the ground 4 I 1 5 / 2 to the 4 I 1 3 / 2 , 4 I 1 1 / 2 , 4 I 9 / 2 , 4 F 9 / 2 , 4 S 3 / 2 , 2 H 1 1 / 2 , and 4 F 7 / 2 excited manifolds were monitored by means of high resolution (as fine as 0.1 cm - 1 ) Fourier Transform spectroscopy in the wave number (6000-22000 cm - 1 ) and temperature (9-300 K) range, respectively. Broad absorption spectra were observed in silica samples simply doped with Er 3 + , as expected for Er 3 + in a glassy environment. In samples containing also SnO 2 nanocrystals, complex, narrow line Er 3 + related spectra were monitored. The lines become sharper and sharper by lowering the temperature to 9 K, as expected for Er 3 + ions embedded in an ordered (crystalline) environment. The nature and origin of different surroundings probed by the Er 3 + line spectra are discussed.

Radio-luminescence, time resolved photo-luminescence and Raman spectroscopy measurements were performed on Ce-doped sol-gel silica glasses. Quenching of the 5d-4f Ce3+ emission transition was observed by increasing Ce3+ concentration above 0.04 mol%, evidenced by a decrease of the emission intensity accompanied by the appearance of a fast component in the photoluminescence time decay. Raman measurements revealed the formation of CeO2 clusters, which can be considered a cause of the observed luminescence quenching. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Sn-doped silica and SnO2:SiO2 glass-ceramics were produced by sol-gel synthesis. Charge trapping and radiative recombinations from ionizing irradiation were investigated in the 8-300 K range. Three radioluminescence (RL) emissions were observed at 1.9, 2.3 and 3.2eV. Dose-dependence of RL shows that the 3.2eV emission grows during the irradiation. 2.3eV RL is the main process at low temperature, whereas it is a minor decay at 300K, as well as in phosphorescence and thermoluminescence. Glow curves show peaks at 80 and 200K. The results suggest that radiative decays and trapping processes occur in the silica network. © 2004 Elsevier B.V. All rights reserved.

SnO 2 –SiO 2 nanostructured glass-ceramics were investigated to verify the suitability as photorefractive material with sensitivity to the visible light. The material was obtained by a sol–gel method and the composite structure was analyzed by means of transmission electron microscopy and Raman scattering. Optical absorption measurements from 200 to 800 nm were analyzed to estimate the effective energy released in the material by laser exposure. Negative refractive index changes (up to −10 −3 ) were observed after exposure to laser beams from the ultraviolet to the green visible spectral range (at 266, 458 and 532 nm). The absorption of visible radiation has larger yield of refractive index change compared to ultraviolet radiation. The results are consistent with the proposal that the refractive index changes involve interface defect states at the surface of SnO 2 clusters with nanometer dimensions.

FTIR spectroscopy was applied in the 500–14,000 cm � 1 range to detect OH vibrational modes (stretching, bending, combination, first and second overtone) in Ce 3+ - and Gd 3+ -doped silicate glasses, prepared by means of the sol–gel technique and aimed to applications as scintillators. The presence of OH groups, belonging either to silanol (Si-OH) or to H2O should be limited, since they could cause radiative emission quenching. The samples, doped with Ce 3+ or Gd 3+ (0.05–3% m.f.), were submitted to thermal treatments at 4501C, 7501C, and 10501C, to remove water and organic groups for producing a dense glass. A large amount of H2O and Si-OH is still present in samples annealed at 4501C and 7501C, while only a reduced quantity of Si-OH (evaluated as o1% m.f.) is detected after annealing at 10501C, i.e. in the final dense glasses (for all concentrations of both dopants). r 2002 Elsevier Science B.V. All rights reserved.

The sol-gel technique has been considered for the preparation of Ce3+-doped silicate scintillating glasses. Ce3+, concentrations in the range 0.1-1 mol% have been studied. The structural and optical properties of the glasses have been investigated by several techniques like Raman spectroscopy, radio-luminescence, time resolved luminescence, and wavelength resolved thermally stimulated luminescence. Particular attention has been paid to the influence of the concentration of dopant ions and to the different phases of the xerogel densification process governing the glass formation. The results achieved indicate that Ce3+ activators possess promising optical features in the considered glass matrix both for what concerns the luminescence efficiency and the scintillation decay time (of approximately 50 ns under Na-22 excitation). (C) 2002 Elsevier Science B.V. All rights reserved.

Vibrational modes of OH, as stretching, bending, combination, and overtones, were monitored by means of FTIR spectroscopy in Ce3 - and Gd3 -doped silicate glasses, prepared by means of the sol-gel technique, submitted to different thermal treatments, and aimed to applications as scintillators. The dopant concentration was varied in a wide range (10 -3 -8% m.f.) and co-doped samples were also investigated. In this framework, the effects of OH and of rare-earth (RE) clustering, i.e. two possible non-radiative decay channels, on the IR spectra in the 500-14 000 cm(-1) were examined. OH was detected as belonging either to water and to silanol in samples densified at 450 and 750 degreesC, while in those treated at 1050 degreesC only Si-OH groups were present in a concentration of the order of 1% m.f., nearly regardless of the RE amount. An absorption peaking at 4250 cm(-1) was identified as related to an OH combination mode (bending???) perturbed by a Gd cluster on the basis of its amplitude dependence on the Gd concentration and rapid thermal treatment.

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.

Radioluminescence optical fibre sensors are gaining importance since these devices are promising in several applications like high energy physics, particle tracking, real-time monitoring of radiation beams, and radioactive waste. Silica optical fibres play an important role thanks to their high radiation hardness. Moreover, rare earths may be incorporated to optimise the scintillation properties (emission spectrum, decay time) according to the particular application. This makes doped silica optical fibres a very versatile tool for the detection of ionizing radiation in many contexts. Among the fields of application of optical fibre sensors, radiation therapy represents a driving force for the research and development of new devices. In this review the recent progresses in the development of rare earth doped silica fibres for dosimetry in the medical field are described. After a general description of advantages and challenges for the use of optical fibre based dosimeter during radiation therapy treatment and diagnostic irradiations, the features of the incorporation of rare earths in the silica matrix in order to prepare radioluminescent optical fibre sensors are presented and discussed. In the last part of this paper, recent results obtained by using cerium, europium, and ytterbium doped silica optical fibres in radiation therapy applications are reviewed.

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.

The reactivity towards CO and air of SnO 2 defects, singly and doubly ionized oxygen vacancies (V o ⋅ V o ⋅⋅ ), bivalent tin centers, was studied in ruthenium-supported tin oxide (Ru/SnO 2 ), and compared with that in pure SnO 2 . Electron paramagnetic resonance and X-ray photoelectron spectroscopy studies demonstrated that CO treatment produces V o ⋅ and V o ⋅⋅ defects in SnO 2 , some V o ⋅ transferring their electrons to Sn 4+ centers; instead in Ru/SnO 2 , some V o ⋅ defects transferred their electrons to Ru n + centers ( n =0,1,2,3) and no one bivalent tin center was observed. When contacted with air, pure SnO 2 transferred a part of the electrons of V o ⋅ and of bivalent tin centers to O 2 , instead Ru/SnO 2 emptied all V o ⋅ defects transferring the electrons from V o ⋅ to ruthenium and to O 2 . The via ruthenium transfer increases the number of electrons exchanged between SnO 2 and the surrounding atmosphere and gave a rationale for the higher sensitivity towards CO displayed by transition metal-doped SnO 2 with respect to pure SnO 2 .

Changes in the photoluminescence (PL) of amorphous SiO2 due to Sn-doping have been investigated by synchrotron radiation. Sn-doped SiO2 samples have been produced by a controlled sol–gel procedure as well as Ge-doped samples prepared for comparison. Detailed maps of the PL and PL excitation pattern have been obtained up to the band-to-band transition energy. The results confirm the analysis of Skuja as regards the emission at 3.1 and 4.2 eV excited at about 5 eV. At higher energies, our data show that the 3.1 and 4.2 eV PL bands have another excitation region with structures at 6.7, 7.2 and 8.0 eV. Lifetimes of about 10 ns for the 4.2 eV PL and 10 μs for the 3.1 eV PL are observed independently of the excitation energy. Data between 10 and 300 K are presented and compared with data from Ge-doped samples. The results show that high energy excitation of the 3.1 eV PL is not thermally activated, in contrast to the 4.9 eV excitation channel. Effects of the different spin–orbit coupling constants at Ge and Sn sites on PL intensity suggest that the high energy excitation channels arise from intra-center singlet-to-singlet transitions.

Optical transitions of radiation-induced paramagnetic Ge centers have been investigated in Ge-doped ${\mathrm{SiO}}_{2}$ samples containing a negligible amount of native oxygen coordination defects, whose optical absorption usually dominates the UV spectral range. The analysis of optical and electron paramagnetic resonance (EPR) spectra following different irradiation and thermal annealing treatments shows that two optical absorptions (at 4.4 and 5.7 eV) are related to an orthorhombic EPR signal [Ge(1) signal in literature], while a band at about 6.3 eV follows the evolution of an axial signal [Ge(3) signal] already attributed to axial ${E}^{\ensuremath{'}}\ensuremath{-}\mathrm{Ge}$ center. No evidence of another orthorhombic EPR signal observed by other researchers [Ge(2) signal] has been found in our samples. Our results suggest that the previous assignments of the 4.4- and 5.7-eV bands to Ge(1) and Ge(2) centers, respectively, be changed. Instead, both electronic transitions are likely to be ascribed to the sites responsible for the Ge(1) signal. This conclusion has been checked by comparing anisotropy and inhomogeneous dispersion of the principal g-tensor values with energy separation and the relative bandwidth and intensity of the optical bands. Structural models of the Ge site responsible for the Ge(1) signal have also been discussed. A structure like the one proposed for the ${E}_{\ensuremath{\alpha}}^{\ensuremath{'}}$ center is suggested, attributing the orthorhombic distortion to a nearby oxygen excess group.

The preparation of Sn-doped SiO2 glasses with different Sn contents (Sn/(SiO2 + SnO2) ratio 0.01 to 10.0% w/w) was performed by two sol-gel routes. The first route (method A) used tin(IV) tert-butoxide as the tin precursor and in the presence of acetylacetone it resulted in transparent glasses with a maximum tin content of 0.1%. The precursor in the second route (method B) was dibutyltin diacetate; this was more efficient and transparent glasses of up to 1% tin content were obtained. As electron paramagnetic resonance can identify paramagnetic E' Sn centres, defects that form when silica glass is subjected to X-ray irradiation, we assessed the tin centres that substituted silicon in the silica network. At higher tin contents (Sn greater than or equal to 3%), method B gave crystalline nanosized particles of SnO2 (6-10 nm) dispersed throughout the silica matrix.