Search

A Bell test is a randomized trial that compares experimental observations against the philosophical worldview of local realism , in which the properties of the physical world are independent of our observation of them and no signal travels faster than light. A Bell test requires spatially distributed entanglement, fast and high-efficiency detection and unpredictable measurement settings. Although technology can satisfy the first two of these requirements, the use of physical devices to choose settings in a Bell test involves making assumptions about the physics that one aims to test. Bell himself noted this weakness in using physical setting choices and argued that human 'free will' could be used rigorously to ensure unpredictability in Bell tests. Here we report a set of local-realism tests using human choices, which avoids assumptions about predictability in physics. We recruited about 100,000 human participants to play an online video game that incentivizes fast, sustained input of unpredictable selections and illustrates Bell-test methodology. The participants generated 97,347,490 binary choices, which were directed via a scalable web platform to 12 laboratories on five continents, where 13 experiments tested local realism using photons, single atoms, atomic ensembles and superconducting devices. Over a 12-hour period on 30 November 2016, participants worldwide provided a sustained data flow of over 1,000 bits per second to the experiments, which used different human-generated data to choose each measurement setting. The observed correlations strongly contradict local realism and other realistic positions in bi-partite and tri-partite 12 scenarios. Project outcomes include closing the 'freedom-of-choice loophole' (the possibility that the setting choices are influenced by 'hidden variables' to correlate with the particle properties), the utilization of video-game methods for rapid collection of human-generated randomness, and the use of networking techniques for

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

Fourier transform absorption spectroscopy in the 500-6000 cm- 1 and 9-300 K ranges is applied to monitor the effects produced by Eu3+ incorporation into sol-gel silica samples doped with concentration increasing from 0.001 to 10 mol%. The aim is to investigate the formation of aggregates by exploiting the Eu3+ crystal-field transitions. Complementary microreflectance and Raman spectra are also measured in the range of silica intrinsic vibrational modes to confirm the hypothesis of matrix modification induced by increasing doping levels. Evidences of clustering are found for high Eu3+ concentrations. Up to 3 mol% the crystal-field line intensities gradually increase and the OH- content smoothly decreases. A further increase to 10 mol% causes drastic, remarkable changes, i.e. sharp crystal-field lines appear which narrow by lowering the temperature. Furthermore, the OH - related bands are no longer detectable. For concentrations up to 3 mol% the aggregates are amorphous as the silica matrix, while for the Eu 3+ 10 mol% sample they show a rather ordered structure. © 2011 Elsevier B.V. All rights reserved.

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.

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.

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.

FTIR spectroscopy is applied to monitor the effects caused by fluorinated precursors (1-10 mol%) in the sol-gel synthesis of silica glasses, either pure or doped with Ce and Er. In pure samples the Si-OH level is heavily reduced to ∼3 × 10-3 mol%. In doped samples the effect is more limited. The presence of residual fluorine, proved by the Si-F vibrational absorption at ∼950 cm-1, causes deep changes in the rare-earth (RE) crystal field spectra, which are characterized by narrow absorption lines. The lines broaden if the temperature is increased from 9 to 300 K. The result is discussed in terms either of local ordering around the rare earth ion or by its partial decoupling from the disordered host matrix, due to the creation of network terminating sites. © 2007 Elsevier B.V. All rights reserved.

The radioluminescence (RL) properties of Ce-doped silica glasses prepared by sol-gel method were investigated as a function of the dopant amount in a wide range of concentrations (Ce:Si molar ratios from 1 x 10(-5) to 5 x 10(-2)). The effects of xerogel densification temperature and of a postdensification thermal treatment were also considered. In order to understand the microstructural features governing Ce3 luminescence efficiency, optical absorption measurements in the ultraviolet, visible, and infrared regions and time-resolved photoluminescence experiments were performed. The complex dependence of RL intensity upon rare-earth (RE) concentration and thermal treatment was attributed to the role of OH vibrations as nonradiative recombination channels, as well as to the formation of RE aggregates in the silica matrix. Specifically, the segregation of CeO2 nanoparticles, in which Ce4 does not supply any radiative emission, has been revealed by infrared absorption measurements, in agreement with previous Raman, transmission electron microscopy, and X-ray diffraction data. Moreover, an optical absorption band, centered at 2.4 eV and whose intensity increases with the square of cerium concentration, was observed and tentatively assigned to an intervalence electron-transfer transition involving Ce3+Ce4 dimers. Postdensification thermal treatments markedly reduce the intensity of this band and increase RL intensity. The relationship between the 2.4 eV band and the RL properties will be outlined. In particular, the increase in RL intensity will be discussed, mainly as a consequence of microscopic modifications leading to an improvement of the charge-transfer efficiency toward emitting centers.

We investigate the effects of erbium doping on SnO2 nanoclustering in Sn-doped silica. Vibrational spectroscopy data from Raman and infrared absorption measurements show nanostructuring effects on the SnO2 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 SnO2 nanophase at low doping levels, whereas at high concentrations it modifies the matrix, hindering the growth of SnO2 crystals and passivating the interface.

Silica glasses containing SnO2 nanocrystals and Er3+ ions were prepared by the sol-gel route and proper annealing treatments. A few samples were prepared with fluorinated Si precursors. Er3+ transitions from the ground 4I15/2 to the 4I13/2, 4I11/2, 4I 9/2, 4F9/2, 4S3/2, 2H11/2, and 4F7/2 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 Er3+, as expected for Er3+ in a glassy environment. In samples containing also SnO 2 nanocrystals, complex, narrow line Er3+ related spectra were monitored. The lines become sharper and sharper by lowering the temperature to 9 K, as expected for Er3+ ions embedded in an ordered (crystalline) environment. The nature and origin of different surroundings probed by the Er3+ line spectra are discussed.