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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.

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.

The triply-doped xTb 3+ /xEu 3+ /xDy 3+ CaWO 4 (x: 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mol%) nanomaterials were prepared at room temperature by a coprecipitation method. The luminescence materials were characterized by X-ray powder diffraction (XPD), thermal analysis (TG), infrared absorption spectroscopy (FTIR) and UV excited photoluminescence. The prepared powder phosphors are single-phase scheelite structure with porous morphology and particle sizes around 11 nm. The materials display white color from cool to the warm white, under UV excitation, as a result of the intraconfigurational 4f transitions from trivalent rare earth ions. The non-radiative energy transfer processes from the O→W and O→Eu LMCT as well as the 4f 8 →4f 7 5d 1 states to the intraconfigurational 4f excited levels of rare earth ions and simultaneous emissions from the 4 F 9/2 (Dy 3+ )→ 5 D 4 (Tb 3+ )→ 5 D 1 , 5 D 0 (Eu 3+ ) emitter levels are reported. Furthermore, CIE parameters and the color correlated temperature (CCT) are discussed in order to characterize the color emission. Based on the results, these luminescence materials may be potential candidates for white light emitting diodes and solid-state lighting.

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.

Rare-earth containing glasses are important materials with technologically relevant combinations of mechanical and optical properties. For developing their functional materials potential it is important to understand the local environment and spatial distribution of the rare-earth ions and their influence upon the structural organization of the glassy matrix. Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) can furnish crucial information about these aspects. In this review we describe the relevant theoretical foundations with a particular focus on rare-earth containing systems. Important experimental approaches covered include dipolar NMR, paramagnetically perturbed NMR, EPR, and hyperfine interaction spectroscopies. These are illustrated in the context of various case studies, including (1) structural features of rare-earth aluminosilicate glasses, (2) spatial distribution and clustering of rare-earth dopants, (3) rare-earth ligand distributions in fluoride phosphate glasses, and structural changes along the glass-to-ceramic transformation in (4) aluminoborate and (5) oxyfluoride glasses.

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.

Precursor glasses with composition Na1+xAlxGe2-x(PO4)3 (NAGP) (0.6 ≤ x ≤ 1.0) are converted into Na-superionic conductor (NASICON) glass-ceramics by thermal treatments with varied duration and annealing temperature. Detailed X-ray powder diffraction with Rietveld refinement and 31P and 27Al solid-state nuclear magnetic resonance (NMR) spectroscopy show that extended annealing at the crystallization temperature leads to a progressive de-alumination, segregation of T-AlPO4 and other crystalline phases, accompanied by the formation of amorphous material. These results suggest that an earlier formed aluminum super-saturated structure equilibrates by losing aluminum upon extended annealing. However, the ionic conductivity of glass-ceramics is less affected than would be predicted by the Al loss encountered in the NASICON phase, suggesting that ionic conductivity in these samples is not only controlled by the composition of the NASICON phase but is further influenced by the other phases present, either by contributing directly to ion transport or by facilitating interparticle contacts.

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.

In the present study the origin of clay deposits occurring in an inland platform, in central Portugal, was investigated by their mineralogical and chemical composition. The clay deposits, exploited for ceramic industry are composed of silt-clay facies, the Monteira Member and the Arroca Member, which are assigned to the Coja Formation (Paleogene) and the Campelo Formation (Miocene), respectively. These clayey facies show almost compositional homogeneity, especially concerning texture. The mineralogical composition of the Monteira Member displays slightly higher content in smectite and interstratified clay minerals, which is supported by the chemical composition of samples analyzed. Both members present similar REE patterns, displaying an intense weathering record and little variation in the source area composition. Minor element geochemistry suggests low content in heavy minerals and transition metals. REE patterns and ratios of geochemical parameters support the dominant metasedimentary provenance, with a granite source contribution and also mature recycled sediments of continental origin. The study results’ suggest that the clays of these two members have the same source in terms of lithology and recycled sediments from the Hesperian massif. During the deposition of the Arroca Member, a major remobilization of the Monteira Member is suggested, explaining the geochemical similarity of both facies.

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.

Herein we report on the crystallized nanoparticles based on Eu 3+ -doped Y 2 O 3 with 5 mol% using citric acid as precursor. The heating temperatures were evaluated in order to obtain the best crystallized nanoparticles with size around 12 nm and with highest red intense photoluminescence emission. Nanocrystallite size was calculated by Scherrer׳s equation based on diffractogram of the material heated at 750 °C for 4 h, obtaining size around 8 nm. The low photoluminescence intense emissions were attributed to the presence of quenchers remaining from precursors used in the synthesis. In general the photoluminescence properties were evaluated based on emission and excitation spectra profile. Rietveld refinement was performed based on the diffractogram of the material annealed at 750 °C for 4 h, and the visualization of the cubic structure was obtained. The centered cubic crystalline structure of Y 2 O 3 was obtained and the photoluminescence properties of Eu 3+ ion in Y 2 O 3 host lattice was verified as being dependent on the temperature of heating and C 2 and S 6 site of symmetry present in the cubic structure. CIE chromaticity diagram was obtained with x and y being 0.682 and 0.316, respectively, for material with the highest relative photoluminescence intensity.

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.

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.