221 research outputs found
Optical investigation of Tb3+-doped Y2O3 nanocrystals prepared by Pechini-type sol-gel process
No full textWe report an optical study of Tb3+-doped Y2O3 nanocrystals synthesized by Pechini-type sol-gel method. The particles are investigated in terms of size and morphology by means of X-ray diffraction and transmission electron microscopy analysis. It is shown how the simple Pechini method allows for the growth of monocrystalline nanoparticles with a volume-weighted average size of about 30 nm. The optical properties of Tb3+ in the host lattice are studied in terms of PL, PLE, and lifetimes. Moreover, a correlation between the type of decay curves, the emission and excitation bands' shapes, and the site location of the emitting Tb3+ in the host material Y2O3 is proposed
Energy transfer between Tb3+ and Eu3+ in co-doped Y2O3 nanocrystals prepared by Pechini method
No full textAbstract Tb3+ and Eu3+ co-doped Y2O3 nanoparticles with a volume-weighted average size of about 30 nm were synthesized via simple Pechini-type sol–gel process. The growth of monocrystalline nanoparticles is investigated via XRD and TEM analysis. The study of energy transfer between Tb3+ and Eu3+ ions was carried out by means of PL, PLE, and photoluminescence decay analyses. The energy transfer from Tb3+ to Eu3+ is efficient and we show how a resonant
type via a dipole-dipole interaction is the most probable mechanism. We compared the energy-transfer efficiencies calculated from the intensities and from the lifetimes of 5D4->7F5 transition of Tb, showing the presence of two populations of Tb, with different local surroundings, in the matrix. Furthermore, the critical distance between Tb3+ and Eu3+ ions has been calculated by means of different theories, from a new probabilistic approach based on the discretization of the theory of Chandrasekhar about the distribution of the nearest neighbors in a random distribution of particles, and from the PL data, suggesting a value of about 7 A
Experimental setup for the measurement of optical properties in the vacuum ultraviolet region
No full textThis work presents an experimental setup designed for measuring optical properties in the vacuum ultraviolet (VUV) region. Originally developed for the characterization of ICARUS photomultiplier tubes, the setup has been recently employed to measure the conversion efficiency of para-Terphenyl coatings, acting as wavelength shifters, as a function of thickness. The VUV region is of particular interest in particle physics experiments utilizing cryogenic noble gases as scintillating media. The setup includes a deuterium light source, a mirror system, an intensity monitor, and a sample chamber to host sample and photodetector. An example measurement of para-Terphenyl conversion efficiency — as wavelength shifter — with varying thickness is presented, demonstrating the versatility and effectiveness of the presented system
Off-Stoichiometry Spectroscopic Investigation of Pure Amorphous Silica and N-Doped Silica Thin Films
No full textCathodoluminescence spectroscopy and X-ray photoelectron spectroscopy were concurrently used to investigate the local physicochemical nature of the amorphous lattice in pure SiO2 and N-doped SiO2 thin films prepared by radiofrequency magnetron sputtering (the latter samples deposited under a set of different conditions of N2 partial pressure). The main aim of this investigation was twofold: (i) to extend our knowledge of the physical and chemical structure of SiO2 films and (ii) to explore our capacity of manipulating, fine tuning, and measuring their stoichiometry characteristics. The presence of nitrogen
atoms in the amorphous host structure was confirmed to significantly affect the formation of oxygen-deficient centers,
nonbridging oxygen hole centers, and other kinds of defect complexes. The main challenge here was to relate the variations in type and concentration of these peculiar defects to the processing conditions and to the amount of nitrogen incorporated in the SiO2 amorphous matrix. The evolution of both pure and doped systems was monitored with increasing the temperature of an annealing cycle following film deposition (1 h in air, at temperatures ranging between 50 and 1200 °C, with 50 °C step).
Stoichiometry changes could thus be clarified and temperature thresholds found for the annihilation of N sites and for the
formation of a pseudoequilibrium stoichiometric structure in silica glass
A goniometric measurement system for reflection, diffusion, and transmission characterization in the VUV range
No full textThe characterization in the Vacuum Ultraviolet (VUV) range of reflection, diffusion and transmission of mechanical components plays a crucial role in understanding and optimizing the performance of particle detectors exploiting the scintillation light coming from liquefied noble gases. To this purpose a goniometric measurement system has been realized. In this presentation, the main technical characteristics and performances of the system are shown together with results coming from preliminary tests on different materials. © 2001 Elsevier Science. All rights reserved
Age-specific anti-hepatitis A (HAV) antibodies seroprevalence in italian travelers. Indications for a rational approach to anti-hepatitis A vaccination
No full textBackground: Hepatitis A virus (HAV) circulation in the environment is decreasing in most industrialized Western countries. This decrease has lead to low seroprevalence rates in adults. As a consequence, many nonimmune unprotected travelers from areas of low prevalence are considered at risk of acquiring HAV infection when traveling to high HAV endemic areas in developing countries. The recent HAV inactivated vaccine has proved safe and effective, and its use in different geographic areas should be guided by local age-specific HAV seroprevalence rates. The aim of this paper is to describe the age-specific sero-epidemiology of HAV infection in travelers from a highly industrialized region in Northern Italy (Lombardy). Methods: Seven hundred and forty-four consecutive travelers aged from 20 to 59 years, subdivided in 10-year age groups, gave blood samples in the collaborative Health Centers in the Lombardy region and sera were tested for HAV IgG antibodies. A questionnaire was given to travelers that investigated alimentary habits and a history of previous travel. Results: Anti-HAV seroprevalence was 18.0%, 58.0%, 75.8%, and 89.5% in the 20-29, 30-39, 40-49, and 50-59 age groups, respectively. Age was the single most important determinant of anti-HAV seroprevalence. The influence of previous travels, eating shellfish, or ingestion of self-cultivated vegetables was ruled out by multivariate analysis. Conclusions: In the Lombardy region (Northern Italy), age specific anti-HAV seroprevalence rates are much higher than those reported in other Western European countries. The cost-benefit analysis suggested that travelers born after 1960 do not need serologic screening before vaccination. Whenever possible, however, HAV serologic screening is advisable for travelers born before 1960. However, the severity of the disease in older subjects, and the proved safety of HAV vaccination in immune subjects, may advise d'emblée HAV vaccination without prior screening, when serologic investigation is unfeasible because of lack of time or the unavailability of testing facilities
A cryogenic system for measuring in the VUV range the absolute quantum efficiency of light detectors with large sensitive area
No full textWe developed a system to measure changes in PMT photocathode's behavior from room to cryogenic temperatures and to determine the absolute quantum efficiency (Q.E.) by comparing the photocathode current with that of a calibrated photodiode. Preliminary test results on the 8-inch Hamamatsu R5912-MOD PMT coated with ≈200μg/cm2 of tetraphenyl butadiene do not show significant variations in Q.E. at cryogenic temperatures with respect to room temperature and are in agreement with other measurements
Thermal-induced local rearrangement in the Er environment of Er-doped silica glass films prepared by PVD
No full textA photon tag calibration beam for the AGILE satellite
No full textThe AGILE satellite will be launched in 2006 for the study of gamma rays in the energy range 30 MeV-50 GeV. The satellite has to be calibrated using gamma rays of known energy. The calibration facility is being developed at the Beam Test Facility (BTF) at the INFN Laboratories in Frascati. The photons are produced by bremsstrahlung of electrons with a maximum momentum of 750 MeV/c. The electrons are tagged using a dipole magnet whose internal walls are covered by microstrip silicon detectors: depending on the energy loss, they impinge on a different strip once the dipole current has been set to a given value. The correlation between the direction of the electron measured by a pair of x-y silicon chambers and the impinging position on the tagging module inside the magnet allows the tagging of the photon. The paper describes the calibration layout and tests and the results, compared with the Montecarlo simulation, in terms of production rate and energy resolution
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