The theory of vibronic transitions in rare earth compounds

The theory of vibronic transitions in rare earth compounds is re-examined in the light of a more reliable representation for the ligand field Hamiltonian than the crude electrostatic model. General expressions that take into account the relevant contributions from the forced electric dipole and dynamic coupling mechanisms are derived for the vibronic intensity parameters. These include additional terms, from charge and polarizability gradients, which have not been considered in previous work. Emphasis is given to the relative signs of these various contributions. Under certain approximations these expressions may be conveniently written in terms of accessible ligand field parameters. A comparison with experimental values for the compounds Cs2NaEuCl6 and LiEuF4 is made and satisfactory agreement between theory and experiment is found. A discussion is given on the sensitivity of the calculated intensities to the values of radial integrals, interconfigurational energy differences and ligand field parameters that may be used. Finally, the problem in which a vibronic and an electronic level are in resonance, or near resonance, is analyzed. Suitable expressions to describe the effects of the even-rank components of the vibronic Hamiltonian are obtained. It is found that, depending on the strength of the vibronic interaction and the resonance conditions, the admixture between these two levels may lead to intensities of nearly equal values. © 1995.

Sorption and preconcentration of some heavy metals by 2-mercaptobenzothiazole-clay

2-Mercaptobenzothiazole loaded on previously treated clay was prepared, characterized and used for sorption and preconcentration of Hg(II), Pb(II), Zn(II), Cd(II), Cu(II) and Mn(II) from an aqueous solution. The support used was a natural clay previously treated with sulphuric acid solution. Adsorption isotherms of metal ions from aqueous solutions as function of pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The chemically treated clay was very selective to Hg(II) in solution in which Zn(II), Cd(II), Pb(II), Cu(II) and Mn(II) were also present. © 1995.

Novel fabrication process of planar waveguides in rare-earth doped fluoroindate glasses

We report the successful fabrication of planar waveguides in rare-earth doped fluoroindate glass substrates. A new procedure for waveguide fabrication using a thermally evaporated AgF nonmetallic film was developed. The refractive index changes of more than 0.03, associated to low propagation losses achieved, open new perspectives and show the potentiality of using this glass family toward further developments in fabrication and design of integrated optical devices for optical communication wavelengths.© 1995 American Institute of Physics.

Lanthanum-lithium-sodium double chromates as ionic conductors

Lanthanum-lithium-sodium double chromates Li1-xNaxLa(CrO4)2 were prepared and analysed by means of admittance spectroscopy. Their a.c. conductivity parameters are correlated with structural details of high and low temperature forms of pure lanthanum-lithium double chromates. Lithium compounds show the lowest conductivity values and the highest activation energy for ion motion, while the sample Li0.5Na0.5La(CrO4)2 exhibits the highest conductivity 10-5 S cm-1 and the lowest activation energy 0.58 eV.

Influence of Earth's shadow on the rotational motion of an artificial satellite perturbed by solar radiation torque

A semi-analytical approach is proposed to study the rotational motion of an artificial satellite under the influence of the torque due to the solar radiation pressure and taking into account the influence of Earth's shadow. The Earth's shadow is introduced in the equations for the rotational motion as a function depending on the longitude of the Sun, on the ecliptic's obliquity and on the orbital parameters of the satellite. By mapping and computing this function, we can get the periods in which the satellite is not illuminated and the torque due to the solar radiation pressure is zero. When the satellite is illuminated, a known analytical solution is used to predict the satellite's attitude. This analytical solution is expressed in terms of Andoyer's variables and depends on the physical and geometrical properties of the satellite and on the direction of the Sun radiation flux. By simulating a hypothetical circular cylindrical type satellite, an example is exhibited and the results agree quite well when compared with a numerical integration. © 1997 COSPAR. Published by Elsevier Science Ltd.

Relative lability of trace metals complexed in aquatic humic substances using ion-exchanger cellulose-hyphan

The purpose of this paper is to characterize the lability/inertness metal fractions complexed by aquatic humic substances (HS) in relation to pH, complexation time, and HS concentration. HS were preconcentrated by ultrafiltration and complexed with bivalent metal ions. These fractions were characterized by ion exchange with the chelating collector cellulose Hyphan by applying batch procedure. The metals were determined by atomic absorption spectrometry. The results show that the distribution coefficients, Kd, decreased with HS presence, and that the relative lability of metal fractions complexed by HS is dependent on variables such as pH, complexation time, and HS concentration. Until c.a. 15 min, the metal change between aquatic HS and ion exchanger occurs following a 2 order reaction. Afterwards, the remaining metal fraction in the HS reacts following a 1st order reaction. For traces of metal ions bound to dissolved HS, the lability orderPb > Mn > Cd, Ni > Cu is revealed. ©1997 Soc. Bras. Química.

Preconcentration of heavy metals ions from aqueous solutions by means of cellulose phosphate: An application in water analysis

Cellulose phosphate (CELLPHOS) was studied as a collector for analytical preconcentration of traces of Cd(II), Cr(III), Cu(II) and Ni(II) from aqueous sample solution. It has been proved that using chromatographic columns packed with CELLPHOS for preconcentration and 1.0 mol 1 -1 HCl for elution the adsorbed analytes are quantitatively enriched. An enrichment factor of 20 (100 ml sample, 5 ml concentrate) was achieved by this separation procedure, which was applied to a series of water analyses (river, sea, bog water).

Frequency upconversion in rare-earth doped fluoroindate glasses

We present recent results on frequency upconversion (UPC) obtained in fluoroindate glasses (FIG) doped with Ho3+, Tm3+ and Nd3+ ions and codoped with Pr3+/Nd3+ and Yb3+/Tb3+ ions. The results for the Ho3+-doped samples show strong evidence of energy transfer (ET) between Ho3+ ions resonantly excited at 640 nm. The origin of the blue-green upconverted fluorescence observed was identified and the dynamics of the signals revealed the pathways involved in the UPC process. In the case of Tm3+-doped FIG, the samples were resonantly excited at 650 nm and the main mechanism that contributes for the red-to-blue upconversion is excited-state absorption (ESA). The FIG samples codoped with Pr3+/Nd3+ were excited at 588 nm in resonance with transitions starting from the ground state of the Nd 3+ and the Pr3+ ions. It was observed that the presence of Nd3+ ions enhanced the Pr3+ emission at 480 nm by two orders of magnitude. Multiphonon (MP)-assisted upconversion is also discussed for Nd3+-doped FIG pumped at 866 nm. Emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. A rate-equation model that includes MP absorption via thermally coupled electronic excited states of Nd3+ was developed and describes well the experimental results. The role played by effective phonon modes is clearly demonstrated. MP-assisted UPC process was also studied in Yb3+/ Tb3+-codoped FIG samples excited at 1064 nm, which is off-resonance with electronic transitions starting from the ground state. It was determined that the mechanism leading to Tb3+ emission in the blue is due to ET from a pair of excited Yb3+ ions followed by ESA in the Tb 3+ ions. © 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS.

Rare earth doped HfO2 nanoparticles embedded in SiO2-HfO2 planar waveguides. Preparation, optical, structural and spectroscopic characterization

In this work we present results on the preparation of planar waveguides based on HfO2 and HfO2-SiO2. Stable sols containing europium and erbium doped HfO2 nanoparticles have been prepared and characterized. The nanosized sol was either deposited (spin-coating) on quartz substrates or embedded in (3-glycidoxipropil)trimethoxisilane (GPTS) used as a hybrid host for posterior deposition. The refractive index dispersion and luminescence characteristics were determined for the resulting HfO2 films. The optical parameters of the waveguides such as refractive index, thickness and propagation losses were measured for the hybrid composite. The planar waveguides present thickness of a few micra and support well confined propagating modes.

Discriminating among earth composition models using geo-antineutrinos

It has been estimated that the entire Earth generates heat corresponding to about 40 TW (equivalent to 10,000 nuclear power plants) which is considered to originate mainly from the radioactive decay of elements like U, Th and K, deposited in the crust and mantle of the Earth. Radioactivity of these elements produce not only heat but also antineutrinos (called geo-antineutrinos) which can be observed by terrestrial detectors. We investigate the possibility of discriminating among Earth composition models predicting different total radiogenic heat generation, by observing such geo-antineutrinos at Kamioka and Gran Sasso, assuming KamLAND and Borexino (type) detectors, respectively, at these places. By simulating the future geo-antineutrino data as well as reactor antineutrino background contributions, we try to establish to which extent we can discriminate among Earth composition models for given exposures (in units of kt · yr) at these two sites on our planet. We use also information on neutrino mixing parameters coming from solar neutrino data as well as KamLAND reactor antineutrino data, in order to estimate the number of geo-antineutrino induced events. © SISSA/ISAS 2003.

Infrared-to-visible frequency upconversion in transparent glass ceramics containing trivalent-rare-earth-doped nanocrystals

In this work we report on visible upconversion emission in Er 3+-, and Ho3+-doped PbGeO3-PbF 2-CdF2-based transparent glass ceramics under 980 nm infrared excitation. In erbium-doped vitroceramic samples, blue(410 ran), green(530, and 550 nm) and red(660 nm) emission signals were generated, which were identified as due to the 2H9/2, 2H 11/2, 4S3/2, and 4F9/2 transitions to the 4I15/2 ground-state, respectively. Intense red(650 nm) upconversion emission corresponding to the 5F5 - 5I8 transition and very small blue(490 nm) and green(540 nm) signals assigned to the 5F 2,3 - 5I8 and 4S2, 5F4 - 5I8 transitions, respectively, were observed in the holmium-doped samples. The 540 nm is the dominant upconversion signal in Ho3+-doped vitroceramics under 850 nm excitation. The dependence of the upconversion processes upon pump power and doping concentration are also investigated, and the main routes for the upconversion excitation processes are also identified. The comparison of the upconversion process in transparent glass ceramics and the precursor glass was also examined and the results revealed that the former present higher upconversion efficiencies.

Non-nutrient heavy metals in tomato plants cultivated in soil amended with biosolid and sugar-cane bagasse compost

In this study, non-nutrient heavy metal concentrations (Cd, Cr, Ni and Pb) were measured in composts during the composting process, in compost/Red-yellow Latosol mixtures, and in tomato plants. Composts were produced using sugar-cane bagasse, biosolids and cattle manure in the proportions 75-0-25, 75-12.5-12.5, 75-25-0, 50-50-0 or 0-100-0 (composts with 0, 12.5, 25, 50 and 100% biosolids). The composts were applied to the soil, in 6 treatments and a control (mineral fertilization). Control and the 0% biosolids treatments received inorganic nitrogen and all the treatments received the same amount of N, P and K. Tomato plants were cultivated in 24-L pots, in a green house in Jaboticabal, SP, Brazil. The experiment had a split plot design, in randomized blocks. Cadmium, Cr, Ni and Pb concentrations were determined during the composting process (7, 27, 57, 97 and 127 days after compost mounting), in soil (0 and 164 days after mixing) and plants. The samples were subjected to digestion with HNO 3, H2O2 and HCl and the metals were determined by AAS. Negative correlations were observed between Cd, Cr and Pb in the compost and Cd, Cr and Pb plant uptake, as well as Ni in the compost and Ni concentration in the plants. The concentrations of Cd, Cr, Ni and Pb increased during composting. Only Cd levels increased when compost was applied to the soil. The roots accumulated Cr, Ni and Pb, the stems and leaves, Cd and Ni and the fruits did not accumulate any of the metals studied. The composts with biosolids did not increase Cd, Cr, Ni and Pb uptake by plants.

Quantitative analysis of potentially toxic metals in alginates for dental use

Alginate is one the materials most employed in practice to make dental impressions. Substances like zinc, cadmium and lead silicate, which are included in several alginate brands with the aim of improving their physical, chemical and mechanical properties, are a source of serious concern as regards their toxicity. The most serious chronic effect of oral exposure to cadmium is renal toxicity. Assimilation of lead has deleterious effects on the gastrointestinal tract, hematopoietic system, cardiovascular system, central and peripheral nervous systems, kidneys, immune system, and reproductive system. Chronic oral exposures to zinc have resulted in hypochromic and microcyte anemia in some individuals. The aim of the present study was to measure the cadmium, lead and zinc contents of seven brands of alginate for dental use on sale in Brazil. The samples were weighed and placed in the Teflon cups of a closed-system microwave oven. Aqua regia (4mL concentrated HCI:HNO3, 3:1 v/v) and hydrofluoric acid (2mL concentrated HF) were added to the samples, which were then subjected to heating. The samples were then cooled to room temperature and diluted to 25 mL in deionized water in a volumetric glass flask. The samples were diluted in duplicate and analyzed against a reagent blank. The analyses were performed in an atomic absorption flame spectrophotometer. Neither lead nor cadmium was detected. Zinc contents ranged from 0.001% to 1.36% by weight. The alginates exhibited low contents of the metals under study and gave no cause for concern regarding toxicity; even so, it is advisable to monitor potentially toxic materials continually and to analyze their plasmatic levels in the professionals working with them.

Heavy metals availability and fractions in soil amended with biosolid composts

The heavy metals when linked to organic matter have a behavior in the soil that is still little known. This study aimed to evaluate the effect of sewage-sludge-based composts when incorporated in the soil, in relation to heavy metals availability. Five composts were incorporated using sugar-cane bagasse, sewage sludge and cattle manure in the respective proportions: 75-0-25, 75-12.5-12.5, 75-25-0, 50-50-0 and 0-100-0 (composts with 0, 12.5, 25, 50 and 100% sewage sludge). The experiment consisted of 6 treatments (5 composts and a control with mineral fertilization) in randomized blocks with a split-plot design. The control and the treatment of 0% sewage sludge received inorganic nitrogen (N). All the treatments received the same amount of N (8.33 g) K (5.80 g) and K (8.11 g) per pot. Tomato plants were cultivated in 24.0 L pots in a greenhouse in Jaboticabal, SP, Brazil. The concentrations of heavy metals were determined in the soil samples at day 0 after compost incorporation. The higher the sewage sludge doses, the higher heavy metal contents in the soil. Among extractants, Melhlich-1 extracted the highest amount of heavy metals, while DTPA extracted the lowest one. The residual fraction presented the highest heavy metal content, followed by Fe oxides crystalline and amorphous to Cu, Cr and Mn, and Mn oxides, and Fe amorphous to Zn, indicating strong associations to oxides and clays. There were significant positive correlations between Mn contents in the plant and Mn linked to Fe oxide amorphous and crystalline.

A study of the relative velocities of small particles that are orbiting the earth

The evolution of the velocity of the particles with respect to the circular orbits of satellites that are around the Earth that the particles will cross, suggests a range of possible velocities of impact as a function of the altitude of the satellite. A study made from those results show that the maximum relative velocities occur at the semi-latus rectum, independent of the initial semi-major axis of the particle. Considering both the solar radiation pressure and the oblateness of the Earth, it is visible that a precession in the orbit occurs and there is also a variation in the eccentricity of the particle as a function of its orbital region and its size. This is important information, because the damage caused in a spacecraft depends on the impact velocity.