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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.

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+.

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.

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.

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.

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 development of integrated photonics and lab-on-a-chip platforms for environmental and biomedical diagnostics demands ultraviolet electroluminescent materials with high mechanical, chemical and environmental stability and almost complete compatibility with existing silicon technology. Here we report the realization of fully inorganic ultraviolet light-emitting diodes emitting at 390 nm with a maximum external quantum efficiency of ~0.3%, based on SnO(2) nanoparticles embedded in SiO(2) thin films obtained from a solution-processed method. The fabrication involves a single deposition step onto a silicon wafer followed by a thermal treatment in a controlled atmosphere. The fully inorganic architecture ensures superior mechanical robustness and optimal chemical stability in organic solvents and aqueous solutions. The versatility of the fabrication process broadens the possibility of optimizing this strategy and extending it to other nanostructured systems for designed applications, such as active components of wearable health monitors or biomedical devices.

The present work reports on the investigation of oxidation states, local symmetry, and optical properties of manganese and iron species in natural cordierite (Mg, Fe) 2 Al 4 Si 5 O 18 , by means of energy-dispersive X-ray fluorescence, electron paramagnetic resonance (EPR), photoluminescence (PL) and optical absorption techniques. In particular, specific EPR characteristics show the presence of distinct Mn 2+ octahedral sites in the crystal lattice, and a small amount of Mn 4+ ions in tetrahedral sites. The absence of EPR signal ascribable to Mn 4+ in octahedral sites turns out to be consistent with the lack of narrow PL lines from d 3 ions in octahedral crystal field (CF). Evidence of Mn 3+ in octahedral sites is instead found in steady-state and time-resolved PL measurements. EPR spectra give further details on iron site occupancy, showing the occurrence of Fe 3+ ions in octahedral sites. Characteristics ascribable to all the identified metal species have been found in the optical absorption spectrum or in the PL excitation spectrum, as arising from the expected CF transitions of Fe 2+ , Fe 3+ , Mn 2+ , Mn 3+ , and Mn 4+ ions. Interestingly, the results show a polarization-dependent correlation between the manganese luminescence and the pleochroic absorption band at about 17,000 cm −1 . This result reveals a pleochroic contribution from the Mn 3+ spin-allowed 5 E→ 5 T 2 transition under the visible pleochroic band attributed to Fe 2+ (oct)→Fe 3+ (tet) transitions.

We present the results of the analysis of the ultraviolet (UV) absorption edge of fluorine-modified sol-gel silica. UV transmission data, obtained by means of synchrotron radiation, have been analyzed in the spectral range 7.5–8.5 eV, with a spectral resolution of about 10 meV. Data on silica samples with different F content (from 0 to few 10 − 1 mol%) have been analyzed and compared with literature data on quartz and pure synthetic commercial silica. The analysis allows us to discriminate between the effects of the fluorine addition and those ascribable to structural peculiarities of the sol-gel networking. The estimated Urbach energy E U ( T = 0) ranges between 45 and 55 meV, higher that in crystalline quartz and lower than in commercial synthetic silica. The study of the temperature dependence of E U ( T ) shows that the fluorine modification of the silica network causes the lowering of the static disorder and the widening of the energy gap. However, there is also a relevant effect of the production process, since sol-gel silica samples show lower E U values with respect to other types of silica, quite independently of the fluorine content. The analysis of the Raman spectra however shows that the starting amount of fluorine-modified molecular precursor influences the network condensation process, independently of the final fluorine content into the matrix.

Positronium (Ps) formation measurements in several porous materials as: Vycor, germanate Xerogel, Metal-Organic Frameworks MOF-177 and Aerogel with two densities (20 and 150 mg/cm3), were performed by means of a variable energy positron beam provided with a Ge detector and a positron lifetime spectrometer. An efficient formation of cooled Ps atoms is a requisite for the production of antihydrogen, with the aim of a direct measurement of the Earth gravitational acceleration g of antimatter, which is a primary scientific goal of AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy). Porous materials are necessary to form a high yield of Ps atoms as well as to cool Ps through collisions with the inner walls of the pores. The different materials were characterized and produce Ps into the pores. Lifetime measurements give an estimation of the typical pores dimension of the substances. A comparative study of the positron lifetime and the Ps fraction values in the above mentioned materials indicates that silica Aerogel, with the appropriate density, is an excellent candidate for an efficient formation of cold Ps atoms for the AEGIS project. © 2010 IOP Publishing Ltd.

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 %.

S. Brovelli,1,2 N. Chiodini,1 F. Meinardi,1 A. Monguzzi,1 A. Lauria,1 R. Lorenzi,1 B. Vodopivec,1 M. C. Mozzati,3 and A. Paleari1 1CNISM–Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 53, I-20125 Milano, Italy 2London Centre for Nanotechnology, and Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom 3CNISM–Department of Physics “Alessandro Volta,” University of Pavia, via Bassi 6, I-27100 Pavia, Italy Received 19 January 2009; published 24 April 2009

We show that Sn O2 nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10-2, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology. © 2006 American Institute of Physics.

A radioluminescent (RL) dosimetric system, based on a SiO2 optical fiber with the core doped by Ce3+ ions as luminescent activators has been investigated. Structural and optical properties of the luminescent fiber have been studied by Raman, refractive index, RL and scintillation time decay measurements, and compared to those obtained on bulk material. The RL response of a composite fiber made of a short portion of active Ce-doped fiber coupled to a long commercial one has been investigated by x-ray irradiation. A linear RL intensity response has been found in the dose rate interval 6x10(-3)-40 mGy/s together with a good radiation hardness, suggesting possible application in low-dose monitoring. (C) 2004 American Institute of Physics.

Optical emissions at 2.1, 2.6, 3.0, and 4.5 eV, excited by synchrotron radiation from 5 to 18 eV, were found in stishovite, a high-density sixfold-coordinated ${\mathrm{SiO}}_{2}$ polymorph. Luminescence and lifetime data were analyzed from 10 to 300 K showing a transition scheme distinct from that of silica, despite some similarities in the spectral positions. The results give a basis for the study of defect structures in sixfold-coordinated ${\mathrm{SiO}}_{2}$ environments, for theoretical calculations of the optical response of high-density ${\mathrm{SiO}}_{2},$ and for a microfluorescence identification of geologic stishovite.

There is considerable interest in Er-doped silica-based materials with photosensitive properties for lasing and photorefractive applications. Tin doping has been recently found to induce strong and stable photosensitivity in silica glass. In this work, Er co-doped Sn-doped silica samples are obtained by sol-gel method by hydrolysis and condensation of TEOS and tin dibutyl diacetate, Er(NO3)3, or Er(CH3 COO)3 as dopant precursors. Samples with Er content ranging between 0.1 and 1 mol% are investigated. Sn doping (0.4 mol%) is employed to induce photorefractivity properties in the glassy host. Time resolved photoluminescence, optical absorption and refractive index measurements are carried out and analyzed as a function of the Er content. The specific effects of Er content and Sn doping on the rare earth emission efficiency and photosensitivity of the glass are discussed. In particular it is shown that the Er emission shows the typical features of Er doped sol gel silica and the strong photosensitivity induced by tin doping is not affected by rare earth ions.

Effects induced by KrF ultraviolet excimer laser on Sn-doped silica fiber performs were analyzed by means of optical and electron paramagnetic resonance (EPR) techniques. Bond breaking in substitutional Sn sites was evidenced by the Sn-E-' EPR signal due to sp(3) unpaired electrons in threefold coordinated Sn sites. Red photoluminescence excited at 633 nm, due to nonbridging-oxygen sites, was also observed after laser exposure. The intensity of this emission did not follow the Sn concentration profile, being observed at the core-cladding interface and in the core center. Birefringence data showed that these effects are accompanied by stress relief in the Sn-doped region. Different structural features of core and cladding were evidenced by micro-Raman measurements and related to the observed photosensitivity. (C) 2000 American Institute of Physics. [S0003-6951(00)00150-9].

Fluorine modified amorphous silica has been synthetized via sol-gel route and studied through analysis of the temperature dependence of the Urbach absorption tail in the vacuum-ultraviolet region. The modified glass has a steep absorption edge above 8 eV, with the absorption coefficient alpha proportional to exp[E/E-U(T)] showing Urbach energy values E-U(T) ranging between 50 and 66 meV. The comparison of E-U(T) with pure silica data indicates a structural softening caused by the reduction of dynamical disorder, and suggests that the F-modified sol-gel synthesis is an appropriate route for achieving high energy shifts of the absorption edge. (C) 2007 American Institute of Physics.

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 investigation of the characteristic luminescent response of Ce-doped silica fibers exposed to electrons in the 20-200-GeV energy range is reported in this work to explore the feasibility of using silica-based fibers for a simultaneous dual-readout approach. The sol-gel method allows the preparation of either doped or undoped fibers with high aspect ratio and high purity, providing good flexibility and spatial resolution for the realization of a dual-readout detector. The dual Cherenkov and scintillation light emitted by silica-based fibers potentially offers applications in high-energy-physics calorimetry as well as in other fields, such as radiation monitoring in medicine, security, and industrial control. The response of the fibers, embedded in a tungsten-copper absorber block to obtain a spaghetti-like geometry in a high-energy-physics environment, is investigated through a test-beam campaign at the CERN Super Proton Synchrotron facility. The discrimination of Cherenkov and scintillation light is demonstrated and discussed, along with a detailed investigation of the scintillation properties of the material: time-resolved spectroscopy, relative light output, and attenuation length are evaluated. The results presented in this study can pave the way for further material engineering and future applications.