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The emission properties of a new phosphor based on LiTaO3:Tb3+ are described. It is shown to be a storage phosphor, i.e., after previous x‐ray exposure, Tb3+ emission in green‐red region of spectrum can be photostimulated by light in 400–800 nm spectral range. Emission centers (Tb3+ ions), electron storage centers (oxygen vacancies) and competing nonradiative recombination centers (oxygen ion and Li vacancy couples), are recognized as the key elements in the energy transfer processes and overall emission efficiency of LiTaO3:Tb3+.

LiTaO3: Tb3+ phosphors, prepared as crystalline powders, exhibit, at room temperature, strong green luminescence both during X-ray exposure (Direct Luminescence, DL) and subsequently, when stimulated in the 400-800 nm range (Photo-Stimulated Luminescence, PSL). Due to the high efficiency of the PSL, similar to that of the well-known UV-blue emitting BaFClxBr1−x:Eu2+ phosphors, the new storage phosphors based on LiTaO3:Tb3+ can find applications as X-ray sensors in Medical Digital Radiography and other radiation sensing fields. Both the direct and photo-stimulated luminescence efficiencies depend on the Li/Ta ratio, on the Tb3+ ions concentration and on the presence of co-dopants like, as in this case, Mg2+ alkali earth ions. Mg2+ ions improve the D.L. and have also a positive effect on the P.S.L. up to a nominal concentration of 0.015-0.02 at/mol. The results of the luminescence properties are here interpreted, with the support of diffuse reflectance data and lattice parameter measurements, on th...

Photo-, radio-, thermo-luminescence properties and afterglow decay kinetics are reported for Gd2O2S:Tb3 X-ray phosphor samples co-doped by Ca2, Ta5, Sn4, and Ru4 ions. A strong influence of co-doping on the optical properties was found, which can be explained by the influence of the excess or lack of charge in the lattice due to aliovalent ions on the concentration of point defects. Possible microscopic processes are proposed. (C) 2003 The Electrochemical Society.

Photo-, radio-, thermo-luminescence properties and afterglow decay kinetics are reported for Gd 2 O 2 S:Tb 3+ X-ray phosphor samples co-doped by Ca 2+ , Ta 5+ , Sn 4+ , and Ru 4+ ions. A strong influence of co-doping on the optical properties was found, which can be explained by the influence of the excess or lack of charge in the lattice due to aliovalent ions on the concentration of point defects. Possible microscopic processes are proposed.

Y 0.6 Gd 0.8 Lu 0.6 SiO 5 :Tb(0.1) belongs to a family of new blue a/o green emitting phosphors constituted by ternary substitutional solid solutions, characterized by high X-ray efficiencies and excellent chemical stability and resistance to exposure damage. Its overall efficiency, measured at 70 KVp on single powder layers, is a factor 1.20 higher than that of a commercial green emitting Gd 2 O 2 S:Tb having similar grain size (3.5 μ, approx.). A value between 0.18 and 0.20 is estimated for the intrinsic conversion efficiency.

The overall, X-Rays to light conversion efliciency and the modulation transfer function of radiographic single front screens have been computed using the Monte Carlo method to simulate the generation and the multiple-scattering diffusion and absorption of light photons in the screen. The computation is based on a set of probability functions related to the absorption of X-Ray photons, free-path lengths and absorption of light photons and reflection conditions at the boundaries. A constant scattering angle has been used for light photons colliding with phosphor grains. For a given phosphor volume fraction, results are shown as a function of phosphor grain size, screen thickness and light wavelength. Some computed results have been checked experimentally.A comparison is made between screens based on mainly green emitting terbium activated gadolinium oxysulphide, and conventional screens based on blue emitting lead activated calcium tungstate. Screens having equal packing volume, thickness and phosph...

Overvoltage measurements in the molten LiF-NaF-KF eutectic mixture,containing oxides, hydroxides and water in solution, were carried out by the galvano Experiments were performed at 600°C on bright platinum electrodes with suitable oxygen or hydrogen electrodes as reference electrode. The results account for the high values of solubility of water and hydrofluoric acid in molten alkali fluorides and give some insight into the kinetics

The solution of trace amounts of samarium (0.1 to 10000 ppm) in forsteritic olivine was investigated by electromotive force galvanic cell measurements. Sm is soluble in olivine up to a concentration limit that is temperature dependent (about 10 ppm at 700°C and 400 ppm at 1000°C) and defined by the solubility of excess silicon in interstitial positions within the structure. The solution can be regarded as “regular” from the thermodynamic point of view, the partial molar entropy of the solute being approximated by the random mixing condition. Within the solid solution range Henry's Law conditions are not observed and the partition coefficients of Sm between olivine and an ideal liquid phase can be expected to decrease with decreasing trace element content in the solid phase.

Electrical conductivity and emf measurements on polycrystalline , as functions of the partial pressure of oxygen, at temperatures ranging between 800° and 1100°C, are used to study some transport and thermodynamic properties of nearly stoichiometric and nonstoichiometric . Due to the localized character of electrons in ionic, hopping‐type semiconductors, results are discussed with a chemical approach, in terms of the dependence of the activation enthalpy for the electrical conductivity and of the activity coefficients of Ni3+ on the partial pressure of oxygen. A defect model for nonstoichiometric is given, which involves the presence of defect clusters (microdomains) with an inverse spinel structure. Furthermore, electrical conductivity results in nearly stoichiometric are presented and discussed, which show straightforward evidence of the influence of iron doping in the range 100–500 ppm on the "intrinsic" character of the electrical conductivity.

E.m.f. measurements on the cell Pt | O2| CaO(+ CaF2)‖ CaF2(tF–= I)‖ ZrO2–CaO | O2| Pt have been carried out in the temperature range 900–1100°C to measure thermodynamic parameters of the lime + zirconia solid solutions and, possibly, to obtain complementary information on the phase-relationships across the concentration range investigated. Results show that the cubic field ranges only between xCaO= 0.14 and 0.17 and that at xCaO= 0.2 a CaZr4O9 phase is probably present. The results are discussed and compared with published data on the topic.