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Owing to their fast but tunable degradation kinetics (in comparison to silicates) and excellent bioactivity, the past decade has witnessed an upsurge in the research interest of borate/borosilicate-based bioactive glasses for their potential use in a wide range of soft tissue regeneration applications. Nevertheless, most of these glasses have been developed using trial-and-error approaches wherein SiO2 has been gradually replaced by B2O3. One major reason for using this empirical approach is the complexity of short-to-intermediate range structures of these glasses which greatly complicate the development of a thorough understanding of composition-structure-solubility relationships in these systems. Transitioning beyond the current style of composition design to a style that facilitates the development of bioactive glasses with controlled ion release tailored for specific patients/diseases requires a deeper understanding of the compositional/structural dependence of glass degradation behavior in vitro and in vivo. Accordingly, the present study aims to decipher the structural drivers controlling the dissolution kinetics and ion-release behavior of potentially bioactive glasses designed in the Na2O-B2O3-P2O5-SiO2 system across a broad compositional space in simulated body environments (pH = 7.4). By employing state-of-the-art spectroscopy-based characterization techniques, it has been shown that the degradation kinetics of borosilicate glasses depend on their R (Na2O/B2O3) and K (SiO2/B2O3) ratios, while the release of particular network-forming moieties from the glass into solution is strongly influenced by their role in-and effect on-the short-to-intermediate-range molecular structure. The current study aims to promote a rational design of borosilicate-based bioactive glasses, where a delicate balance between maximizing soft tissue regeneration and minimizing calcification and cytotoxicity can be achieved by tuning the release of ionic dissolution products (of controlled identity and abundance) from bioactive glasses into physiological media.

The quaternary rare earth nickel aluminum germanide series RENiAl4Ge2 (RE = Y, Sm, Gd–Tm, Lu) has been extended by several members. The compounds were synthesized from the elements by arc-melting, and single crystals of YNiAl4Ge2, GdNiAl4Ge2, and LuNiAl4Ge2 were grown from an aluminum flux. All members crystallize isostructurally in the rhombohedral SmNiAl4Ge2-type structure (R3̅m, Z = 3). The compounds can be described as a stacking of RE δ+ and [NiAl4Ge2] δ− slabs with an ABC stacking sequence, or alternatively as stacking of CsCl and CdI2 building blocks. The results of the magnetic measurements indicate that all rare earth atoms are in a trivalent oxidation state. Of the RENiAl4Ge2 series, the members with RE = Sm, Gd–Dy exhibit antiferromagnetic ordering with a maximum Néel temperature of T N = 16.4(1) K observed for GdNiAl4Ge2. 27Al NMR spectroscopic investigations yielded spectra with two distinct signals, in line with the crystal structure, however, significantly different resonance frequencies of δ iso ms(YNiAl4Ge2) = 77(1) and 482(1) ppm as well as δ iso ms(LuNiAl4Ge2) = 90(1) and 467(1) ppm were observed. These indicate significantly different s-electron densities at the two crystallographically different Al atoms, in line with the results from DFT calculations. The Bader charge analysis confirms that the present compounds must be considered as germanides, as expected from the relative electronegativities of the constituent elements, while the low charges on Al and Y indicate significant covalent bonding.

The beneficial effect of magnesium oxide upon the performance of crack-resistant oxide glasses has been explored in a series of aluminoborosilicate glasses with the compositions 60SiO2–(20 – x)Al2O3–xB2O3–20Na2O and 60SiO2–(20 – x)Al2O3–xB2O3–10Na2O–10MgO. The simultaneous presence of both boron and aluminum oxides in these glasses produces a synergetic effect upon crack resistance (CR), whose structural origins are being explored by detailed 11B, 23Na, 27Al, and 29Si single and double resonance solid-state NMR studies. Aluminum is exclusively four-coordinated, whereas boron is found in both three- and four-coordination. Substitution of B2O3 with Al2O3 and Na2O with MgO leads to a dramatic reduction of N4, the fraction of four-coordinate boron, accompanied by an increase in CR. 11B/27Al double resonance NMR studies show only weak interactions between the boron oxide and aluminum oxide components, giving no evidence of the formation of new structural units not already realized in the ternary aluminosilicat...

Rare earth elements (REE) are a group of the periodic table formed by 17 chemical elements (lanthanoids plus yttrium and scandium). They have been used in different field applications. In agriculture, they can be found in some phosphate fertilizers at levels one or two orders of magnitude higher than those found in normal agricultural soils. Citrus plants are known to present high levels of REE when compared to most other species, however, there is little information about bioavailability of REE in phosphate fertilizers for citrus plants. This work focuses on the study of REE behavior by the application of increasing doses of single superphosphate fertilizer in Rangpur lime (Citrus limonia Osbeck) plants in a greenhouse study. The technique used was instrumental neutron activation analysis (INAA). The results showed that the fertilizer has caused significant increases in the content of REE in the citrus plant tissues, with higher concentrations in leaves than in branches. The highest substrate-leaf transfer factor was observed for La (0.0047), though the concentrations in the plants followed the same order found in the substrate, i.e. Ce > La > Sm > Eu > Sc. There was an increase of rare earth elements concentrations in Rangpur lime plants by superphosphate fertilizer application.

Designing an effective and simple detection method to quantify glyphosate (GLY) herbicide is desirable. Current chromatography-mass spectrometry and electrochemical methods can be used for this purpose, but these methods are difficult to be made portable and need high-cost equipment. Here, we evaluate a luminescent β-diketonate-Eu-ethylenediaminetetraacetic acid complex for GLY quantification in aqueous media on the basis of the luminescent quenching process. This complex successfully measured GLY at concentrations ranging from 5 × 10-7 to 10-5 mol L-1. Theoretical methods (LUMPAC) are also performed to identify the complex most probable structure in solution. We also demonstrate that the metal-organic frameworks HKUST-1 and IRMOF-3, easily synthesized, effectively adsorb GLY in water in about 30 min of contact.

Rare Earth-containing materials exhibit interesting luminescence properties, such as a spectral profile with narrow emission lines and a well understood crystal field dependence. These features make them appealing materials for molecular probing. Here, the structural properties governing the luminescence of Eu3+ ions hosted in layered double hydroxides (LDH) are investigated. Eu3+-substituted LDH have been shown to present photoluminescence properties dependent on the anionic species intercalated between the hydroxide layers. This feature is shown by the characterization and comparison between LDH intercalated with NO3− and a set of benzenecarboxylates: trimesate (benzene-1,3,5-tricarboxylate, BTC), trimellitate (benzene-1,2,4-tricarboxylate, TLA) and terephthalate (benzene-1,4-dicarboxylate, TERE). Successful LDH formation and intercalation with the respective anion was confirmed by powder X-ray diffraction (PXRD). The coordination structure of Eu3+ has been investigated by Extended X-ray Absorption Fine Structure (EXAFS) experiments, showing the incorporation of this activator in the hydroxide layers of the LDH in an 7/8-fold Oxygen-rich environment. The systems here investigated present very similar coordination, except for the presence of a water related Oxygen at around 3.0 A in the nitrate-intercalated LDH, absent in the benzenecarboxylate-intercalated materials. The photoluminescence properties of all samples were analysed on the basis of the Judd-Ofelt theory, showing that the polycarboxylate- and NO3−-intercalated LDH can be grouped into two distinct classes with different sets of Judd-Ofelt intensity parameters (Ω2 and Ω4). This has been rationalized based on the EXAFS results. Symmetry distortions in the first coordination shell of Eu are also expected from the observed changes in Ω2 and Ω4. This distinctive feature allows one to probe interlayer modifications in LDH through changes in the luminescence properties of lanthanide activators hosted in their hydroxide layers, opening up new opportunities for in-situ investigation of anion exchange reactions in these materials.

While the versatile composition of layered double hydroxides (LDHs) allows to introduce almost any polyvalent cation in their structure, the exchangeable negatively charged ions intercalated between the plates increase their vast range of functionalities. The combination of these features can be simultaneously tuned for the desired application. Here we report on the preparation and optical properties of pillared Eu3+-doped ZnAl LDHs intercalated by aliphatic dicarboxylates: ‒OOC‒(CH2)n–2‒COO‒. The basal distance in these materials is dependent on the size and packing of the intercalated anions. By varying the number (n) of Carbon atoms in the aliphatic chain from 2 to 12, the interlayer gallery of these ZnAlEu LDHs is considerably expanded from 0.9 to 2.1 nm. In the interlayer gallery, the aliphatic dicarboxylates form a monolayer, with the aliphatic chain inclined by an angle α ≈ 63° with the hydroxide layers. The Carbon atom in the COO– group is 0.43 nm far from the metal plane, showing that these carboxylates are not grafted in the brucite-like layers. These LDHs are thermally stable up to around 150 °C, after which dehydroxylation of the hydroxide layers is observed. The Judd-Ofelt intensity parameters were obtained and compared to the Eu3+-containing complexes with the same ligand series indicating a more symmetrical and less polarizable chemical environment around the rare earth ion.

Despite the favorable NMR-spectroscopic features of the 9Be isotope, the exploration of solid Beryllium compounds by this method has been very limited, owing to safety concerns regarding their preparation and handling. The present review aims to be the first comprehensive one on this topic, summarizing the classical and modern methodologies available for determining the relevant 9Be NMR observables in the solid state. Results on molecular crystals, oxidic materials, and intermetallic systems will be discussed in terms of their informational content in relation to atomic and electronic structure and dynamics, leading to suggestions for future paths of investigation.

We show in this paper that the valence state of Mn is determinant for the optical response of Zn1−xMnxO thin films. In addition, thermal treatment is an efficient way to tailor these properties. This investigation examines the valence change of manganese in Zn1−xMnxO thin films at concentrations up to x = 0.7 after annealing by correlating reference samples: Mn3O4 and ZnO. The thin films were grown by spray pyrolysis using an aqueous-acetate route on glass substrates. A phase transition from Mn3O4 (hausmannite) to $$\alpha$$ -Mn2O3 (bixbyite) occurs after annealing, while Zn1−iMnxO keeps the wurtzite phase. X-ray photoelectron spectroscopy indicates that as-grown Mn oxide sample exhibits both Mn2+ and Mn3+ species with a predominance of Mn2+ while annealed Mn oxide presents Mn3+ and Mn4+. The presence of Mn2+ in as-grown Mn-doped ZnO is also confirmed by electron paramagnetic resonance. Scanning electron microscopy and optical absorption measurements show that the annealing on ZnMnO has the same influence as solely Mn oxide. The occurrence of Mn segregation is attributed to the predominance of Mn3+in the annealed system.

Rare earth elements plus yttrium (REY) mass fractions of ancient carbonate rocks are used to track changes in chemistry of past seawater. Here we investigate REY patterns in two carbonate sections from the Ediacaran Bambui Group, Sao Francisco Basin (Brazil), which comprise its two lowermost transgressive-regressive second-order sedimentary sequences. Shale normalised distributions vary with the sequence stratigraphy framework. In the basal 2nd-order sequence, carbonate samples from the basal sequence transgressive systems tract display light REY (LREY) distributions slightly depleted to enriched that reflect input of freshwater, possibly in a post glacial episode. Upwards, carbonate rocks from the early highstand systems tract (EHST) yielded LREY enriched distributions, which progressively turns into LREY shale normalized depleted distributions on samples from the late highstand systems tract (LHST). This portion of the sequence also displays Y positive anomaly in some cases. Carbonate samples from the upper second-order sequence do not display coherent patterns. Ce/Ce* values > 1 in most samples throughout the two sections suggest permanent anoxia of seawater. The REY change from the EHST to LHST in the basal sequence marks an important paleoenvironmental overturn in the basin, with increasing alkalinity in seawater driving REY fractionation and LREY depletion. Confinement of the basin in the inner areas of West Gondwana due the uplift of marginal neoproterozoic orogens probably changed the weathering style of source areas to more congruent, thus delivering a higher ionic influx to a restricted setting, increasing alkalinity during LHST. Cloudina sp. fragments were reported in this stage of the Bambui Group and in carbonate rocks with high Sr mass fractions in other West Gondwana basins, supporting the hypothesis that the high alkalinity of seawater during late Ediacaran may have driven the appearance of the first biomineralizing organisms.

Made available in DSpace on 2021-06-25T10:16:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-11-19 Bismuth-containing rare-earth codoped fluoride phosphate glasses are promising materials for superbroadband near-infrared (NIR) emission with potential applications in optical amplification. To elucidate their structural organization, this contribution develops a comprehensive multinuclear solid-state single and 31P/19F double resonance NMR strategy, applied to glasses in the system (BiF3)y(50NaPO3-20Ba(PO3)2-20NaF-10BaF2)100-y (y = 0, 5, 10, 20, 30, 40). To separately assess the influence of bismuth and fluorine constituents on the network structure, an additional set of (NaPO3)50-2x(Ba(PO3)2)20-x(NaF)20+2x(BaF2)10+x (x = 0, 2.5, 5.0, 7.5) glasses was also investigated. Introduction of alkali fluoride ions into phosphate glasses is shown to follow a new network modification scheme involving depolymerization of polyphosphate chains under the formation of F-bonded fluorophosphate units. However, a significant part of the fluoride stays separate, interacting exclusively with metal-ion species. 23Na MAS and 23Na{31P} double resonance NMR results are consistent with a local sodium ion environment dominated by phosphate ions in the Bi-free system, whereas in the BiF3-containing glasses, the successive reduction of the dipolar second moment M2(Na-P) with increasing BiF3 content reflects the expected dilution effect, accompanied by increasing competition of the fluoride ions for ligation with the Na+ ions. São Carlos Institute of Physics São Paulo University-USP, Avenida Trabalhador Saocarlense 400 Institut für Physikalische Chemie Westfälische Wilhelms-Universität Münster, Corrensstrasse 30 Institute of Chemistry São Paulo State University-UNESP, Avenida Professor Francisco Degni, 55 Institute of Chemistry São Paulo State University-UNESP, Avenida Professor Francisco Degni, 55

Mangroves are intertidal tropical ecosystems influenced by marine and terrigenous input. They are important sinks of trace elements, like Rare Earth Elements (REE), which are recognized as excellent indicators of geochemical processes in estuaries. REE data of bulk soil samples from eight mangroves located along the Brazilian coast were correlated with quantitative clay mineral data based on XRD full-profile modelling. Kaolinite has been found to transform to Fe-illite in these mangroves. The clay assemblage was dominated by interstratified phases, including kaolinite-smectite (kaolinite and smectite-rich), illite–smectite and other illitic phases. REE concentrations in bulk soils were LREE > MREE > HREE (where L, M and H indicate light, medium and heavy). Multivariate statistical approach (PCA analysis) using clay mineral concentrations and proxies for relative REE concentrations ([La/Gd]N, [La/Yb]N and [Gd/Yb]N ratios) showed (r > 0.75) that fractionation of LREE over HREE was highest in mangroves where kaolinite, fed with the highly weathered sediments form the Neogene Barreiras Group, was most abundant (67–85% of all clay minerals), while REE fractionation decreased as the relative proportion of Fe-rich smectite increased (26–46 % of all clay minerals). Identified processes of REE control are: 1) Level of sediment weathering within the continent, where higher weathering implies higher kaolinite content and higher REE fractionation (LREE > MREE > HREE); 2) selective leaching of LREE from mangrove soils by saline water; 3) preferential adsorption of HREE by Fe-rich smectite and illite neoformed in the mangrove soils. It is possible to conclude that clay minerals exert an important control on REE fractionation in tropical mangroves.

The structure of binary (SiO2)100-x–(P2O5)x glasses has been investigated by Raman scattering, 29Si and 31P magic angle spinning (MAS) as well as static 31P NMR spectroscopy. 29Si chemical shift trends reflect the successive replacement of Si–O–Si by Si–O–P linkages as the compositional parameter x is increased. While 31P MAS NMR does not resolve separate phosphate species, the static 31P NMR lineshapes were successfully simulated by considering the effect of uncorrelated distribution functions of the chemical shift tensor components upon the line shape. On the basis of these simulations, which were also found to be consistent with the experimental 31P MAS NMR spectra, two distinct sites can be resolved: a dominant site characterized by an axially symmetric chemical shift tensor, assigned to P(3) units, and (only in the case of the x = 25 and 30 glasses) a Gaussian component reflecting phosphate species interacting with five- and six-coordinated silicon species. For 0 ≤ x < 25, the decrease in average coo...

We report near-infrared to ultraviolet (UV) upconversion emissions in triply-doped Gd3+–Tm3+–Yb3+ fluoride–phosphate glasses. Emission at 310 nm, originated from the Gd3+:6P7/2 → 8S7/2 transition, was observed for the first time in glasses. The high-purity glasses prepared exhibit extended transparency in the UV down to 200–250 nm. The mixed fluoride–phosphate environment of the rare-earth ions was characterized by means of NMR techniques using scandium as a diamagnetic mimic for the luminescent species, for which the ligand distribution was quantified by 45Sc{31P} rotational echo double-resonance NMR. Both the intensity of the Gd3+ emission as well as those of the UV emissions at 290, 347, and 363 nm increase with increasing ratio of fluoride to phosphate ligands coordinating to the rare-earth ion.

High photoluminescence efficiency, unusual NIR broadband and tunable emission are possible in erbium-doped and tantalum germanate glasses and nanostructured glass-ceramics. The chemical microenvironment around erbium ions and their influence on optical properties are dependent on the TaO6 clusters formation and tantalum perovskite-like bronze crystallization, which are strongly related to the tantalum oxide content and annealing. Erbium ions are preferably distributed close to tantalum-rich environment, providing an intense emission with minimized nonradiative processes and inhomogeneous broadband NIR emission with increasing site numbers. A more pronounced broadening in the nanocrystalline samples is due to the multi-sites of the tantalum perovskite-like bronze crystalline structure. Green/red tunable emission from up conversion processes was observed since the erbium ions occupy a chemical environment with low phonon energy in the tantalum germanate glass and with close neighbors in the tantalum germanate glass-ceramics. Accordingly, the highly tantalum germanate glasses and glass ceramics are promising for photonic applications in optical amplification, lighting and lasing, as well as for nonlinear optical applications and studies considering the perovskite-like bronze crystalline samples.

A detailed structural investigation of a series of fluoride phosphate glasses with nominal compositions 25BaF2-25SrF2–(30–x)Al(PO3)3–xAlF3–(20–z)ScF3:zREF3 with x = 25, 20, and 15, RE = Yb and Eu, and 0 ≤ z ≤ 1.0, and of a Sc-free set of glasses with compositions w[80(Ba/Sr)F2–20AlF3]–(1–w)[80Ba(PO3)2–20Al(PO3)3] (w = 25, 50, 75), doped with 0.2 mol % Yb3+ or Eu3+, has been conducted. As indicated by Raman scattering and solid state NMR, the network structure is dominated by aluminum–oxygen-phosphorus linkages, which can be quantified by means of 27Al/31P NMR double resonance techniques. The ligand environment of the rare-earth ions is studied by (1) 45Sc NMR of the diamagnetic mimic Sc3+, (2) pulsed X-band EPR spectroscopy of Yb3+ spin probes, and (3) excitation and emission spectroscopy of Eu3+ dopants. The rare-earth ions are found in a mixed environment of fluoride and phosphate ions, which changes systematically as a function of glass composition. In the Sc-containing glasses the quantitative makeup ...

Made available in DSpace on 2020-12-10T20:13:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-26 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Deutsche Forschungsgemeinschaft A detailed structural investigation of two series of fluoride phosphate glasses with nominal compositions 20BaF(2)-20SrF(2)-20ZnF(2)-xIn(PO3)(3)-(40 - x)InF3 (x = 0, 5, 10, and 15) and 20BaF(2)-20SrF(2)-20ZnF(2)-10ScF(3)-xIn(PO3)(3)-(30 - x)InF3 (x = 0, 10, 15, 20), both doped with either 0.2 mol % Yb3+ or 0.S mol % Eu3+, has been conducted. As indicated by Raman scattering and solid- state NMR, the network structure is dominated by six-coordinated In3+, orthophosphate Q((0)()) species, and the (near) absence of P-O-P connectivity. The ligand environment of the rare-earth ions is studied by (1) Sc-45 NMR of the diamagnetic mimic Sc3+, (2) echo-detected field-sweep EPR spectra at the X-band, using Yb3+ spin probes, and (3) excitation and emission spectroscopy of Eu3+ dopants. Sc-45{P-31} rotational echo double resonance (REDOR) results, the ratio of the Eu3+ D-5(0) -> F-7(2) to (5) D-0 -> F-7(1) emission intensities, the lifetime values of the Eu3+ emitting level D-5(0), as well as the g factor measured by EPR spectroscopy consistently indicate that the fluoride ligands strongly dominate in the first coordination sphere of the rare-earth ions. This result stands in contrast to previous studies on aluminofluorophosphate glasses with similar compositions that show mixed ligation of the rare-earth ions by fluoride and phosphate ions. Thus, by substituting aluminum by its homologue indium one can achieve the original design goal of fluoride phosphate glasses, which is the creation of a framework structure dominated by oxide, while the local environment of the RE emitting ion is dominated by fluoride ligands, so as to improve their emissive properties. The results also illustrate the successful use of the previously developed combined NMR/EPR/optical characterization strategy for the design of optimized matrices for rare-earth ion emitters. Univ Sao Paulo, Inst Fis Sao Carlos, Ave Trabalhador Saocarlense 400, BR-13566590 Sao Carlos, SP, Brazil Univ Estadual Paulista, Inst Quim, Rua Prof Francisco Degni 55, BR-14800060 Araraquara, SP, Brazil Westfalische Wilhelms Univ Munster, Inst Phys Chem, Corrensstr 30, D-48149 Munster, Germany Univ Estadual Paulista, Inst Quim, Rua Prof Francisco Degni 55, BR-14800060 Araraquara, SP, Brazil FAPESP: 2018/03931-9 FAPESP: 2018/24735-3 FAPESP: 2017/06649-0 CNPq: 406611/2017-3 Deutsche Forschungsgemeinschaft: 413550885 FAPESP: 2013/07793-6

Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive Na2O–ZnO–Al2O3–SiO2 glass, containing NaF and KBr additives, along with cerium, silver, tin, and antimony oxide dopant...

Actual acid mine drainage (AMD) containing a high concentration of sulfate (∼1,000 mg·L−1), dissolved metals, uranium, rare earth elements and yttrium (REY) was treated using a down-flow fixed-structured bed biological reactor (DFSBR). The reactor was operated in a continuous flow mode for 175 days and the temperature was maintained at 30 °C. The synthetic AMD was gradually replaced by the actual AMD in 20, 50 and 75% of the total medium volume. Sugarcane vinasse was used as the electron donor and the influent pH of the reactor was decreased from 6.9 to 4.6 until the system collapsed. REY elements and transition metals were removed from the actual AMD and precipitated in the down-flow fixed-structured bed reactor. Sulfate reduction achieved 67 ± 22% in Phase II and chemical oxygen demand (COD) removal was above 56% in Phases I and II. Removal of La, Ce, Pr, Nd, Sm and Y was higher than 70% in both Phases II and III while Fe, Al, Si and Mn were removed with efficiencies of 79, 67, 48 and 25%, respectively. The results highlighted the potential use of DFSBR in the treatment of AMD, providing possibilities for simultaneous sulfate reduction and metal and REY recovery in a single unit.

This work proposes a smart way to produce lanthanide-doped alumina and yttrium spherical compounds. We were able to tune the structure of the Al2O3-yttrium binary material prepared herein by controlling the Y3+/Al3+ ratio. Small ratio (Y0·1/Al1 mol/mol) afforded the metastable hexagonal phase (YAlO3), which remained stable in the final product even after thermal treatment at 1100 °C. On the basis of XRD data, increasing Y3+/Al3+ ratio led to the formation of the crystalline YAG phase after thermal treatment. The luminescence data showed that Eu3+ ions doped into the binary material were highly sensitive to changes in the environment around the Eu3+ ion, and the emission spectra corroborated that the latter ion migrated to yttrium sites in the YAG structure. The luminescence confirmed the presence of a secondary Eu3+ ion coordination site in the material, but at higher Y3+/Al3+ ratio, the YAG structure has predominated.

The structure of glasses in the systems (100 – x)B2O3–xPbF2 (x = 30, 40, and 50) and 50B2O3–(50 – x)PbO–xPbF2 (x = 5, 10, 15, 20, 25, 30, 35, 40, and 45) has been studied by solid state NMR and EPR spectroscopies. On the basis of 11B and 19F high resolution solid state NMR as well as on 11B/19F double resonance results, we develop a quantitative structural description on the atomic scale. 19F NMR results indicate a systematic dependence of the fluoride speciation on PbF2 content: At low x-values, F– ions are predominantly found on BO3/2F– units, whereas, at higher x-values, fluoride tends to be sequestrated into amorphous domains rich in PbF2. In addition, both pulsed EPR studies of Yb3+ doped glasses and photophysical studies of Eu3+ doped samples indicate a mixed fluoride/borate coordination of the rare-earth ions and the absence of nanophase segregation effects.

The structural aspects of the glass-to-crystal transition of Na2O-2CaO-3SiO2 (1-2-3) and 2Na2O-CaO-3SiO2 (2-1-3) glasses have been investigated using X-ray diffraction and multinuclear NMR spectroscopy. These materials represent a small group of glasses that undergo homogeneous nucleation rather than following the thermodynamically favored path of surface crystallization. To understand this unusual nucleation mechanism the structural resemblance of the glasses and their isochemical crystals was probed on different length scales. Definitive evidence of structural similarity at the level of intermediate-range order is obtained from 23Na spin echo decay experiments, which are sensitive to the spatial distribution of the sodium nuclei. In contrast the distributions of the silica network former units are quite different in the glassy and the crystalline states. These results suggest that a structural resemblance of the short- and intermediate-range order of the network modifiers rather than the network formers may be a key feature of homogeneously nucleating glasses.

Tungsten-phosphate glasses doped with different rare earth ions (Er3+, Eu3+, Nd3+ and Tb3+) were obtained by the conventional melt-quenching technique. At high amounts of tungsten oxide (>50 mol%), the tungsten-phosphate glasses are only translucent due to reduced W5+ species. However, the transparency of the glasses is significantly increased by the addition of Sb2O3 - as an oxidating agent which promotes the conversion of W5+ into W6+. FTIR spectra allowed identification of absorption bands corresponding to phosphate structural groups and tungsten units in the 500–1300 cm−1 spectral region. The optical absorption, luminescence excitation and emission spectra were collected and Judd-Ofelt analysis was carried out for selected samples. It is observed that by increasing the amount of WO3, the lifetime of the Er3+ NIR emission increases as well as the branching ratio of Eu3+ emission band at 610 nm, respectively, due to lowering of the average phonon energy of the glassy system and increasing of the site asymmetry around the rare earth ions. Details on the photophysics of these glasses, including upconversion and the analysis of radiative properties via Judd-Ofelt calculations are given and discussed as a function of structural variations and dopant ion concentrations.

Sodium phosphosilicate glasses with high phosphate contents represent an unusual case in glass science as they are known to contain large amounts of six-coordinated silicon species (SiO6/2 units, Si(6)). Although the network connectivity of these units has been previously investigated, the overall structural organization of this system at the medium-range order level is still incompletely understood. In the present study, this issue is addressed by using a comprehensive suite of homo- and heteronuclear dipolar recoupling studies involving the nuclear isotopes 23Na, 29Si, and 31P on isotopically enriched glasses in the systems xSiO2–(1 – x)(0.45Na2O–0.55P2O5) (x = 0.0, 0.1, and 0.2) and 0.2SiO2–0.2Na2O–0.6P2O5. Four- and six-fold coordinated silicon species (Si(4) and Si(6)) coexist in these glasses. Invariably, Si(6) selectively connects with phosphate species, which are exclusively of the P(3) type, whereas the Si(4) species are coordinated to both P(2) and P(3) units. 29Si ↔ 23Na and 31P ↔ 23Na rotation...

The coordination network consisting of trivalent bismuth ions and pyromellitic acid (H4Pyr), [Bi(HPyr)], was successfully applied as a host matrix for in situ incorporation of trivalent rare earth (RE3+) ions Sm3+, Eu3+, Tb3+ and Dy3+. High-throughput methods for hydrothermal synthesis allowed us to prepare and study the phase purity and crystallinity of the sample series, accelerating and facilitating the comparison between the synthesis parameters. Infrared absorption spectroscopy, elemental and thermogravimetric analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy, as well as powder X-ray diffraction and refinement of the unit cell parameters of the compounds, indicated that doping did not affect the structure, crystallinity, morphology and thermal stability of the matrix. The study of the spectroscopic luminescence properties of the nondoped and doped [Bi(HPyr)] allowed investigation of the sensitization processes of dopant RE3+ ions. The characteristic spectroscopic properties of the Eu3+ ion were used to study the incorporation site and coordination environment of the dopant by calculation of the experimental intensity parameters Ωλ (λ: 2 and 4) and intrinsic quantum yield of the Eu3+ single-doped [Bi(HPyr)]. Straightforward emission color tuning by changing the relative concentrations of the dopant ions is possible and has been studied for the four systems double-doped with Tb3+:Eu3+, Tb3+:Sm3+, Dy3+:Eu3+ and Dy3+:Sm3+ ions. The Dy-containing systems show different shades of white emission and a wide range of correlated color temperatures (CCT), ranging from 2500 to 7500 K, hence being a promising candidate for the development of single-phase white light emitting devices.

New lanthanide-based luminescent coordination compounds containing thiabendazole (TBZ) as ligand were synthesized. Elemental analysis, mass spectrometry, thermogravimetric analysis and infrared spectroscopy were important for structural elucidation, providing the following chemical structures: [Eu(TBZ)2(NO3)3]·H2O and [Tb(TBZ)2(NO3)3]·H2O, called as EuTBZ and TbTBZ, respectively. Photoluminescence spectroscopy was also performed. EuTBZ and TbTBZ emitted characteristic red (618 nm) and green (542 nm) light, corresponding to chromaticity coordinates (0.57; 0.40) and (0.23; 0.54), respectively. Emission quantum efficiency of EuTBZ 5D0 was 57%. TbTBZ showed higher quantum yield than EuTBZ, 35% against 0.2%. Forensic tests were performed using TbTBZ as a marker in the 9 mm ammunition allowing visualizing luminescent gunshot residues (GSR) on the target, weapon and cartridge. It can help experts in analyzing crime scene, directing GSR collection and providing an optical and chemical signature to GSR derived from non-toxic ammunition.

Network former mixing effects in Yb3+-doped glasses in the system [(2TeO2)x(P2O5)1–x]0.6[(PbO)0.5-(ZnO)0.5]0.4 have been investigated using a comprehensive strategy involving complementary NMR (31P,125Te, 207Pb) and EPR (of Yb3+ probe ions) spectroscopies. Phosphate local environments and connectivities are extracted from detailed 31P MAS NMR line shape analyses with assignments to distinct PnmTe sites supported by recoupling of homonuclear spin–spin interactions (refocused-INADEQUATE experiments). These results suggest a preference for P–O–Te over P–O–P and Te–O–Te connectivities for x 0.6, where the anionic fraction of phosphate exceeds the expected fraction (67%) based on composition. On a local scale, nonlinear trends...

The local structure of the model glasses (NaPO3)1–x-(AlF3)x (0 ≤ x ≤ 0.4), prepared by standard melt-cooling, was extensively investigated by high-resolution solid-state nuclear magnetic resonance (NMR) including advanced double-resonance techniques. This glass system offers the opportunity of studying five different heteronuclear distance correlations (Na–F, Na–P, P–F, Al–F, and P–Al) by 10 distinct double-resonance experiments, involving all of the constituent elements present. 27Al MAS-NMR data indicate that aluminum is predominantly six-coordinated. According to 27Al{31P} and 27Al{19F} rotational-echo double-resonance (REDOR) spectroscopic results, two to three Al–F and three to four Al–O–P linkages occur in these glasses, independent of composition x. 19F MAS-NMR spectra show the presence of terminal P-bound and Al-bound fluorine species. A small amount of fluorine bridging to two aluminum octahedra, which could be assigned based on 19F{27Al} and 19F{31P} REDOR experiments, was also detected. 19F{23N...

Rare earth (RE3+)-doped fluorophosphate glasses are among the most promising candidates for high-efficiency laser generation in the near-infrared spectral region. By proper choice of composition, these materials can combine the advantages of fluorides (low phonon energies, low refractive indices, extensive optical window, low hygroscopicity) and of oxides (high chemical and mechanical stability and high dopant solubility), resulting in enhancement of the RE3+ emissive properties. In this work, we present the synthesis and structural/spectroscopic investigation of new glasses with composition 25BaF225SrF2(30-x)Al(PO3)3xAlF3(20-z)YF3:zREF3, where x = 20 or 15, RE = Er3+ and/or Yb3+, z = 0.25–5.0 mol%. Results indicate considerable improvement of the emissive properties of both ions when compared to phosphate or even other fluorophosphate host compositions. Long excited state lifetimes (τ = 10 ms for the Er3+ level 4I13/2, and τ = 1.3 ms for the Yb3+ level 2F5/2) imply high fluorescence quantum efficiencies η (up to 85% for both ions). Structural characterization by Raman and multinuclear solid state NMR spectroscopies indicate that the metaphosphate-type chain structure of the Al(PO3)3 vitreous framework is partially depolymerized and dominated by Q(0) and Q(1) units crosslinked by six-coordinate Al species. As revealed by 27Al{31P} rotational echo double resonance (REDOR) NMR results the average local aluminum environment of the x = 20 sample comprises 1.6 phosphate and 4.4 fluoride species. These results indicate a clear bonding preference between aluminum and phosphorus, which is consistent with the desired dominance of fluoride species in the local environment of the rare earth and alkaline earth atoms in these glasses.

High red photoluminescence emission has been obtained at room temperature in Eu3+-doped yttrium oxide thin films following thermal treatment. Films with different thicknesses were deposited on Si(1 0 0) and Si(1 1 1) substrates via electron beam evaporation in a vacuum environment. The films were subsequently annealed in an oxygen atmosphere for 5 h at 900 °C. The structural and optical properties of the films were measured before and after annealing. An improvement in the emission intensity was observed as a result of the thermal treatment under a controlled atmosphere. This observation is related to the reduction of non-radiative processes, as verified by the enhancement of the 5D0→7F2 lifetime values. This improvement in the emission intensity was also analyzed in terms of electric and magnetic dipole transitions (5D0→7F2 and 5D0→7F1 level transitions, respectively). Both transitions are directly related to the site symmetry and, consequently, to the crystalline structure of the films deposited on the Si(1 0 0)/Si(1 1 1) substrates.

Alkaline earth fluorides are extraordinarily promising host matrices for phosphor materials with regard to rare earth doping. In particular, quantum cutting materials, which might considerably enhance the efficiency of mercury-free fluorescent lamps or SC solar cells, are often based on rare earth containing crystalline fluorides such as NaGdF4, GdF3 or LaF3. Substituting most of the precious rare earth ions and simultaneously retaining the efficiency of the phosphor is a major goal. Alkaline earth fluoride nanoparticles doped with trivalent lanthanide ions (which are required for the quantum cutting phenomenon) were prepared via a microwave assisted method in ionic liquids. As doping trivalent ions into a host with divalent cations requires charge compensation, this effect was thoroughly studied by powder X-ray and electron diffraction, luminescence spectroscopy and 23Na, 139La and 19F solid state NMR spectroscopy. Monovalent alkali ions were codoped with the trivalent lanthanide ions to relieve stress and achieve a better crystallinity and higher quantum cutting abilities of the prepared material. 19F-magic angle spinning (MAS)-NMR-spectra, assisted by 19F{23Na} rotational echo double resonance (REDOR) studies, reveal distinct local fluoride environments, the populations of which are discussed in relation to spatial distribution and clustering models. In the co-doped samples, fluoride species having both Na+ and La3+ ions within their coordination sphere can be identified and quantified. This interplay of mono- and trivalent ions in the CaF2 lattice appears to be an efficient charge compensation mechanism that allows for improved performance characteristics of such co-doped phosphor materials.

In this work a pigment material, cerium phosphate (CePO4) was investigated as a new UV filter with excellent morphological characteristics, desirable UV absorption features, low toxicity, and ideal particle size for application in sunscreen formulations. To this end, nanostructured CePO4 were synthesized by two different procedures: the Pechini (modified) method with, varying calcination temperatures (700–900 °C), and hydrothermal synthesis with different Ce 3 + | P 3 O 10 5 − molar ratios, 1:1 and 1:2. The samples were characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, and photocatalytic activity. The excellent morphological properties, low photocatalytic activity, and high absorption in the UV region of the resulting compound indicated the possible application of CePO4 as a UV filter in sunscreen formulations, in order to substitute the currently employed inorganic UV filters ZnO and TiO2.

Highly luminescent rare earth (R3+) doped alkaline-earth tungstates MWO4:R3+ (M2+: Ca, Sr and Ba, R3+: Eu, Tb, Gd) were prepared with a room temperature coprecipitation method. The phosphors were characterized by X-ray powder diffraction (XPD), thermal analysis (TG), infrared absorption spectroscopy (FTIR) and UV excited photoluminescence. The as-prepared MWO4:R3+ particles belong to the tetragonal scheelite phase, and are well crystallized and are of the average size of 16–48 nm. The excitation and emission spectra of the materials were recorded at 300 and 77 K temperatures. The luminescent materials exhibit intense red (Eu3+) and green (Tb3+) colors under UV excitation. The excitation spectra of the Eu3+ doped materials show broad bands arising from the ligand-to-metal charge transfer transitions (O2−→WVI and O2−→Eu3+) as well as narrow bands from 4f–4f intraconfigurational transitions of Eu3+. 4f–4f emission data of the Eu3+ and Tb3+ in the MWO4 host matrices as well as the values of emission quantum efficiencies of the 5D0 level and the 4f–4f experimental intensity parameters of Eu3+ ion are presented and discussed.

Analytical methods for the determination of rare earth elements (REE) in natural waters by plasma spectrochemical techniques often require sample preparation procedures for analytes preconcentration as well as for removing matrix constituents, that may interfere on the analytical measurements. In the present work, calcium alginate (CA) beads were used for the first time aiming at Ce, La and Nd preconcentration from groundwater samples for further determination by inductively coupled plasma optical emission spectrometry (ICP OES). Test samples were analyzed in batch mode by transferring a 40 mL test portion (pH=5±0.2) into a 50 mL polyethylene flask containing 125 mg CA beads. After 15 min contact, the analytes were quantitatively extracted from the loaded CA beads with 2.0 mL of 1.0 mol L −1 HCl solution for further determination by ICP OES, using Ce (II) 456.236, La (II) 379.478 and Nd (II) 430.358 nm emission lines. The proposed approach is a reliable alternative for REE single-stage preconcentration from aqueous samples, as it provided accurate results based on the addition and recovery analysis of groundwater. The results obtained by the proposed method were also compared with those from reference method based on inductively coupled plasma mass spectrometry (ICP-MS) and no significant differences were observed after applying the Student’s t -test at 95% confidence level.

Pt–Ln/C (Ln = La, Ce, Pr, and Eu) catalysts were obtained by using a modification of the polyol method and tested for ethanol oxidation. Transmission electron microscopy (TEM) results showed that the Pt–Ln/C catalysts had particles with average size of 3 nm, which is the smallest particle size reported for Pt–rare earth catalysts; and the particles are homogeneously distributed on the carbon support. X-ray diffraction analysis showed no alloy formation between Pt and rare earth elements, and X-ray photoelectron spectroscopy (XPS) confirmed that Ln is present in its oxide form. X-ray absorption spectroscopy (XAS) results confirmed that the presence of the second metal affects the Pt electronic structure. CO oxidation in the presence of rare earths takes place mostly through the lower-potential pathway, and these catalysts showed better activity toward ethanol oxidation than Pt/C with the same particle size. Durability tests performed by repetitive potential cycling under an Ar atmosphere revealed good structural stability of the Pt–Ln/C catalysts.

[RE(TLA)·(H2O)n:Eu3+] (RE3+: Y, Gd and Lu; TLA: trimellitic acid) precursor complexes were synthesized by an one step aqueous co-precipitation method. After annealing for 1 h, RE2O3:Eu3+ nanophosphors were formed through the benzenetricarboxylate low temperature thermolysis method (500-1000 oC). The compounds were characterized by using different techniques [elemental analysis (CHN), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG/DTG), X-ray powder diffraction (XPD) and scanning electron microscope (SEM)]. The XPD data indicated that the Y2O3:Eu3+ materials have crystallite size range from 11 to 62 nm. The SEM and transmission electron microscopy (TEM) images show that the annealed materials keep morphological similarities with the precursor complexes. The photoluminescence properties were studied based on the excitation and emission spectra, and luminescence decay lifetimes of the 5D0 emitting level of the Eu3+ ion. The experimental intensity parameters (Ωλ), lifetimes (τ), as well as radiative (Arad) and non-radiative (Anrad) decay rates were calculated and discussed. The RE2O3:Eu3+ phosphors (RE: Y3+ and Lu3+) annealed at 500 to 1000 oC have emission quantum efficiency (intrinsic quantum yield) values from 60 to 82%, indicating that this material can be potentially used for optical markers applications.

The design of bifunctional magnetic luminescent nanomaterials containing Fe3O4 functionalized with rare earth ion complexes of calixarene and β-diketonate ligands is reported. Their preparation is accessible through a facile one-pot method. These novel Fe3O4@calix-Eu(TTA) (TTA = thenoyltrifluoroacetonate) and Fe3O4@calix-Tb(ACAC) (ACAC = acetylacetonate) magnetic luminescent nanomaterials show interesting superparamagnetic and photonic properties. The magnetic properties (M-H and ZFC/FC measurements) at temperatures of 5 and 300 K were explored to investigate the extent of coating and the crystallinity effect on the saturation magnetization values and blocking temperatures. Even though magnetite is a strong luminescence quencher, the coating of the Fe3O4 nanoparticles with synthetically functionalized rare earth complexes has overcome this difficulty. The intramolecular energy transfer from the T1 excited triplet states of TTA and ACAC ligands to the emitting levels of Eu(3+) and Tb(3+) in the nanomaterials and emission efficiencies are presented and discussed, as well as the structural conclusions from the values of the 4f-4f intensity parameters in the case of the Eu(3+) ion. These novel nanomaterials may act as the emitting layer for the red and green light for magnetic light-converting molecular devices (MLCMDs).

Fractionation of Rare Earth Elements (REE) and the accumulation and translocation indexes were measured and determined in the native vegetation [Halimium lasianthum (Lam.) Spach subsp. alyssoides (Lam.) Greuter; Cytisus multiflorus (L’Hér.) Sweet; and Cistus monspeliensis L.; Cistus ladanifer subsp. ladanifer; Lavandula stoechas L.] from the iron mining area of Moncorvo (NE Portugal). There is no correlation between the amounts of REE in rhizosphere and in plants. The REE concentration as the fractionation follows roots>leaves>stems in plants. A slightly enrichment in HREE were found in rhizosphere and plants (roots and stems), whereas the leaves are enriched in LREE. The accumulation and translocation depend of internal complexes ligands. The redox and pH conditions of the rhizosphere conditioned the REE uptake. Greatest bioaccumulation ability of heavy REE (HREE) was found in C. monspeliensis, followed by H. lasianthum that also, has a high capacity of the REE translocation to the aerial parts, contrary to C. monspeliensis. An M-type tetrad effect was determined mainly for HREE (Gd-Ho series) indicating a complexation of REE. The greatest differences in the REE fractionation patterns (mainly for HREE) are observed in stems, as a consequence of the transport function of this organ. Cerium anomaly indicates that the pH and redox conditions affected the uptake of Ce by plants, where the free ionic species are dominated in roots and leaves (positive anomaly), and stems (negative anomaly). Also the Eu-anomaly is greater in roots and leaves than in steams probably by participation in metabolic functions due to similarity with calcium.

The effect of the band gap on the persistent luminescence of cadmium meta- and orthosilicates was studied with VUV–UV–vis photoluminescence and x-ray absorption spectroscopies (XANES and EXAFS). The narrower band gap of Cd2SiO4 is favourable for persistent luminescence from Pr3+ but not from Tb3+ due to the trivalent rare-earth energy level positions in the band gap.

Biopolymer-based membranes have particular interest due to their biocompatibility, Biodegradability, easy extraction from natural resources and low cost. The incorporation of Er 3+ ions into natural macromolecule hosts with the purpose of producing highly efficient emitting phosphors is of widespread interest in materials science, due to their important roles in display devices. Thus, biomembranes may be viewed as innovative materials for the area of optics. This paper describes studies of luminescent material DNA-based membranes doped with erbium triflate and demonstrates that their potential technological applications may be expanded to electrochromic devices. The sample that exhibits the highest ionic conductivity is DNA 10 Er, (1.17 × 10 −5 and 7.76 × 10 −4 S.cm −1 at 30 and 100 °C, respectively). DSC, XRD and POM showed that the inclusion of the guest salt into DNA does not change significantly its amorphous nature. The overall redox stability was ca. 2.0 V indicating that these materials have an acceptable stability window for applications in solid state electrochemical devices. The EPR analysis suggested that the Er 3+ ions are distributed in various environments. A small ECD comprising a Er 3+ -doped DNA-based membrane was assembled and tested by cyclic voltammetry and chronoamperometry. These electrochemical analyses revealed a pale blue color to transparent color change and a decrease of the charge density from -4.0 to -1.2 mC.cm −2 during 4000 color/bleaching cycles.

White light emitting rare earth anhydrous complexes RE(TMA):Dy3+ (RE3+ = Y3+ and Lu3+) containing the trimesic acid ligands (TMA) were synthesized and characterized by elemental analysis, X-ray diffraction patterns, thermogravimetric analysis and infrared spectroscopy. The crystallinity and thermostability of these luminescent materials were determined. Since the first excited triplet state (T1: 24,000 cm−1) of TMA ligand is located at higher energy than the main emitting 4F9/2 level (21,000 cm−1) of the Dy3+ ion, TMA can act as efficient luminescent sensitizer in the intramolecular energy transfer of RE(TMA):Dy3+ material. The near-white emission colour originated from the intraconfigurational transitions of Dy3+ ion 4F9/2→6HJ is discussed.

Structural, spectroscopic and dielectric properties of thulium-doped laser-heated pedestal Ta2O5 as-grown fibres were studied. Undoped samples grow preferentially with a single crystalline monoclinic structure. The fibre with the lowest thulium content (0.1 at%) also shows predominantly a monoclinic phase and no intra-4f12 Tm3+ recombination was observed. For sample with the highest thulium amount (1.0 at%), the appearance of a dominant triclinic phase as well as intraionic optical activation was observed. The dependence of photoluminescence on excitation energy allows identification of different site locations of Tm3+ ions in the lattice. The absence of recombination between the first and the ground-state multiplets as well as the temperature dependence of the observed transitions was justified by an efficient energy transfer between the Tm3+ ions. Microwave dielectric properties were investigated using the small perturbation theory. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for thulium-doped Ta2O5 samples it decreases to 18 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. FCT - PTDC/CTM/66195/2006 FCT - PTDC/FIS/66262/2006 FCT - PTDC/FIS/72843/2006

This work aims at the geochemical study of Pitinga cryolite mineralization through REE and Y analyses in disseminated and massive cryolite ore deposits, as well as in fluorite occurrences. REE signatures in fluorite and cryolite are similar to those in the Madeira albite granite. The highest ΣREE values are found in magmatic cryolite (677 to 1345 ppm); ΣREE is lower in massive cryolite. Average values for the different cryolite types are 10.3 ppm, 6.66 ppm and 8.38 ppm (for nucleated, caramel and white types, respectively). Disseminated fluorite displays higher ΣREE values (1708 and 1526ppm) than fluorite in late veins(34.81ppm). Yttrium concentration is higher in disseminated fluorite and in magmatic cryolite. The evolution of several parameters (REEtotal, LREE/HREE, Y) was followed throughout successive stages of evolution in albite granites and associated mineralization. At the end of the process, late cryolite was formed with low REEtotal content. REE data indicate that the MCD was formed by, and the disseminated ore enriched by (additional formation of hydrothermal disseminated cryolite), hydrothermal fluids, residual from albite granite. The presence of tetrads is poorly defined, although nucleated, caramel and white cryolite types show evidence for tetrad effect.Este trabalho enfoca a geoquímica de elementos terras raras (ETR) e de Y no minério criolítico disseminado, no depósito criolítico maciço e na fluorita associada na mina Pitinga. As assinaturas de ETR na criolita e fluorita são similares àquelas do granito Madeira. Os maiores valores de SETR são encontrados na criolita magmática disseminada (677 a 1.345 ppm); SETR é menor na criolita maciça, com valores médios de 10,3 ppm, 6,66 ppm e 8,38 ppm, respectivamente, nos tipos de criolita nucleada, caramelo e branca. A fluorita magmática disseminada apresenta os valores mais altos de SETR (1.708 e 1.526 ppm), contrastando com a fluorita de veio tardio(34,81 ppm). A concentração de Y é maior na fluorita disseminada e na criolita magmática. As evoluções de diversos parâmetros (SETR, ETRL/ETRP, Y) podem ser seguidas através dos sucessivos estágios de evolução dos albita granitos e mineralização associada. Os dados de ETR indicam que o depósito criolítico maciço foi formado por, e o minério disseminado enriquecido por (formação adicional criolita disseminada hidrotermal), fluidos hidrotermais residuais do albita granito. A presença do efeito tetrad não é bem definida, embora as criolitas maciças nucleada, caramelo e branca apresentem algumas evidências deste efeito.

Tests are described showing the results obtained for the determination of REE and the trace elements Rb, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th and U with ICP-MS methodology for nine basaltic reference materials, and thirteen basalts and amphibolites from the mafic-ultramafic Niquelândia Complex, central Brazil. Sample decomposition for the reference materials was performed by microwave oven digestion (HF and HNO3, 100 mg of sample), and that for the Niquelândia samples also by Parr bomb treatment (5 days at 200°C, 40 mg of sample). Results for the reference materials were similar to published values, thus showing that the microwave technique can be used with confidence for basaltic rocks. No fluoride precipitates were observed in the microwave-digested solutions. Total recovery of elements, including Zr and Hf, was obtained for the Niquelândia samples, with the exception of an amphibolite. For this latter sample, the Parr method achieved a total digestion, but not so the microwave decomposition; losses, however, were observed only for Zr and Hf, indicating difficulty in dissolving Zr-bearing minerals by microwave acid attack. Les Terres Rares et les elements en trace suivants: Rb, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb, Th et U, ont ete analyses par ICP-MS dans neuf materiaux de reference de composition basaltique et treize basaltes et amphibolites du Complexe basique -ultrabasique Niquelândia (centre du Bresil). Les materiaux de reference ont ete mis en solution par attaque acide dans un four a micro ondes (HF et HNO3, 100 mg d'echantillon) et ceux de Niquelândia l'ont ete aussi par attaque dans des bombes Parr (5 jours a 200°C, 40 mg d'echantillon). Les resultats obtenus sur les materiaux de reference sont identiques aux valeurs publiees, montrant que la technique d'attaque par micro onde peut etre appliquee en toute confiance aux roches basaltiques. Aucun precipite de fluorure n'a ete observe dans les solutions resultantes de l'attaque par micro onde. L'extraction des elements a ete totale, meme pour Zr et Hf, pour les echantillons de Niquelândia, sauf pour une amphibole ou seule la methode d'attaque avec la bombe Parr a permis une extraction totale. Neanmoins, les pertes ne concernaient que Zr et Hf, revelant donc une certaine difficulte de la technique d'attaque par micro onde a detruire les mineraux contenant Zr.

Aluminato de zinco dopado com os íons terras raras itérbio e érbio nas proporções 2:1, 3:1, 4:1, e 5:1 mol de Yb:Er foi sintetizado por reação de combustão. O efeito da dopagem simultânea Yb:Er na estrutura e na morfologia do aluminato de zinco foi investigado. Os pós foram sintetizados com base nos conceitos da química dos propelentes e então caracterizados por difração de raios X, análise granulométrica, adsorção de nitrogênio (método BET) e microscopia eletrônica de varredura. Os resultados mostraram a formação da fase cristalina majoritária de ZnAl2O4:Yb:Er e traços das fases secundárias ZnO e Yb2O3 e que o aumento da relação Yb:Er favoreceu o aumento das fases secundárias. Todas as composições apresentaram morfologia formada por aglomerados moles constituídos por partículas finas. A área superficial aumentou em função da elevação da proporção Yb:Er.

Ao longo dos anos, o Instituto de Pesquisas Energéticas e Nucleares (IPEN/CNEN-SP) tem realizado diversas pesquisas na produção de Terras Raras (RE) de alta pureza. A metodologia apresentada neste trabalho refere-se à produção econômica e de baixo custo de óxido de cério. O cério produzido pode ser utilizado como um padrão espectroquímico. A obtenção desse padrão está associada à precipitação fracionada pelo sistema RECl3/NH4OH/Ar/H2O2, para enriquecer o óxido de cério de 90% a 99,99% em CeO2. O controle de qualidade do padrão produzido é feito através da técnica da espectrometria de massas com fonte de plasma (ICP-MS) e confirmado pela técnica da ativação de nêutrons. Os valores das impurezas de Terras Raras no óxido, em ppm são: La(36), Pr(19), Nd(161), Sm(11), Eu(5,3), Gd(113), Tb(89), Dy(2), Ho(0,05), Er(1), Tm(

The laser heated pedestal growth technique was used to obtain single crystal fiber of M-type GdTaO 4 . The fibers were around 3 cm long, ∅0.8 mm, transparent, colorless and did not exhibit any inclusions. The structural quality of the fibers was evaluated by X-ray rocking curve profiles and X-ray topography. Better quality crystals were grown perpendicular to (0 1 0) direction presenting rocking curve FWHM typically around 52 arcsec for the ( 3 2 ¯ 3 ) reflection. The results confirm that good structural fibers can be successfully obtained by the procedure presented here.

This paper presents the study on lithium triborate glass (LBO) in the system (1-x)|3B2O3.Li2O| (x)Nb2O5 yPr3+ zYb3+ wNd3+ with 0 £ x £ 20 mol% (y, z and w in mol%). The samples were studied by Raman spectroscopy, infrared absorption and differential thermal analysis. Pr3+-doped LBO and Pr3+/Yb3+-doped LBO samples show an increase of the glass transition and crystallization temperatures and a decrease of the fusion temperature associated with the increase of the praseodymium concentration in the LBO matrix. For the Nd3+-doped LBO and Pr3+/Yb3+-doped (LBO+Nb2O5) samples, a decrease of the glass transition temperature of the samples was observed. The increase of the rare earth doping leads to an increase of the difference between the glass transition and the crystallization temperatures. From infrared analysis it was possible to identify all the modes associated to the B-O structure. The NbO6 octahedra was also identified by IR spectroscopy for samples with x=5, 10, 15 and 20 mol% and y=0.05, z=1.1 mol%. Raman spectroscopy shows the presence of boroxol rings, tetrahedral and triangular coordination for boron. For samples containing niobium, the Raman spectra show the vibrational mode associated with the Nb-O bond in the niobium octahedra (NbO6). Este trabalho apresenta um estudo de vidros de triborato de lítio (LBO) do sistema (1-x)|3B2O3.Li2O| (x)Nb2O5 yPr3+ zYb3+ wNd3+ com 0 £ x £ 20 mol% (y, z e w em mol%). Foram feitos estudos por espectroscopia Raman, absorção no infravermelho e análise térmica diferencial. Amostras de LBO dopadas com Pr3+ e com Pr3+/Yb3+ mostram um aumento nas temperaturas de transição vítrea e de cristalização e uma diminuição na temperatura de fusão associada ao aumento da concentração de praseodímio ma matriz de LBO. Foi observada uma diminuição na temperatura de transição vítrea nas amostras de LBO dopadas com Nd3+ e nas de (LBO+Nb2O5) dopadas com Pr3+/Yb3+.O aumento no teor de dopagem de terras raras leva a um aumento na diferença das temperaturas de transição vítrea e de cristalização. A análise de espectroscopia na região do infravermelho possibilitou identificar todos os modos associados à estrutura B-O. O octaedro NbO6 foi também identificado por espectroscopia de infravermelho nas amostras com x=5, 10, 15 e 20 mol% e y=0,05, z=1,1 mol%. Os resultados de espectroscopia Raman mostram a presença de anéis boroxol, e coordenação tetraédrica e triangular para o boro. Para as amostras contendo nióbio, os espectros Raman mostram o modo vibracional associado com a ligação Nb-O no octaedro de nióbio (NbO6).

O comportamento à corrosão de cerâmicas à base de Si3N4 contendo misturas de Y2O3/SiO2 e RE2O3/SiO2 como aditivos nas proporções de 14 e 21% em volume ambos na estequiometria dos dissilicatos Y2Si2O7 e RE2Si2O7, respectivamente, foi estudado em soluções aquosas de HCl 0,1N a 100 °C. A resistência à corrosão foi avaliada pela perda de massa das amostras e análise química das soluções após os testes. As análises por microscopia eletrônica das amostras atacadas revelou que basicamemte a fase vítrea intergranular foi dissolvida pela solução ácida, deixando um esqueleto de grãos de b-Si3N4 entrelaçados. The corrosion resistance of Si3N4 ceramics with 14 and 21 vol.% of Y2O3/SiO2 and RE2O3/SiO2 mixtures as additive, both in the stoichiometry of disilicates Y2 Si2O7 and RE2Si2O7, respectively, has been investigated in 0.1N HCl solutions. Samples were prepared by a two step gas pressure sintering process, under a final N2 pressure of 10 MPa and a maximum temperature of 1850 °C for 30 min. The corrosion resistance was evaluated by the mass change of polished samples and chemical analysis of the solutions after the tests. Analysis by electron microscopy showed that the glassy intergranular phase is dissolved by the acid solution, leaving a skeleton of interlinked b -Si3N4 grains.

Petrographic studies and SEM/EDS and XRD analyses revealed the presence of a phosphate with Ca and REE (La, Nd) in a mudstone deposit of the Resende Formation, located on the northern border of the Resende Basin. The morphological characteristics (prismatic hexagonal habit) and chemical composition of the phosphate allow including this mineral in the rhabdophane group. This phosphate is authigenic and its origin is related to the dissolution of detritic apatite grains, probably by alkaline hydrothermal solutions. These solutions also provided some of the elements involved in the rhabdophane crystalization.