Preparation, patterning and luminescent properties of nanocrystalline Gd2O3:A (A=Eu, Dy, Sm, Er) phosphor films via Pechini sol–gel soft lithography

Nanocrystalline Gd₂O₃:A (A=Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd₂O₃ phosphor films due to an efficient energy transfer from Gd₂O₃ host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu³⁺, Dy³⁺, Sm³⁺, Er³⁺ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd³⁺ in Gd₂O₃ films, respectively.     

A novel chromatographic separation technique using tertiary pyridine resin for the partitioning of trivalent actinides and lanthanides

A novel chromatographic separation technique using a tertiary pyridine type resin has been applied to the partitioning of the trivalent actinides (An) and lanthanides (Ln) and several successful results have been shown. In an alcoholic hydrochloric acid system, the trivalent An were clearly separated from the Ln, while no such group separation was achieved in an alcoholic nitric acid system. On the other hand, the nitric acid system was more effective for the intragroup (i.e. individual) separation of the trivalent An and the Ln than the hydrochloric acid system. On the basis of these results, a novel concept for the partitioning of the trivalent An and Ln using the present separation technique and its flowchart have been proposed with its advantages and disadvantages.     

The influence of erbium doping of Al-N sputtered coatings on their optical properties

Room-temperature photoluminescence (PL) measurements were performed on erbium-doped AlN thin films deposited by r.f. reactive magnetron sputtering on steel and amorphous quartz substrates. The Al/(N+Al) ratio in the as-deposited films varies in the range from 0.48 to 0.51, while erbium content ranges from 0.2 to 3.5 at.%. X-ray diffraction showed that the AlN(Er) films with erbium contents up to 1.4 at.% have the hexagonal AlN crystalline structure and a preferential orientation following the [0 0 1] direction. However, as a consequence of lattice distortion and/or defect generation originated by the incorporation of erbium atoms in the AlN structure, the films became amorphous for higher erbium contents. All the as-deposited films exhibited room-temperature PL at 1.54 μm, indicating that at least part of the erbium species are optically active in the as-grown samples. Subsequent annealing of the films led to an intensification of the PL signal up to a factor of 6 for the films heat-treated at 1075 K. Within the range of chemical compositions studied in this work, the PL signal increased with increasing erbium content. A weak green visible PL was also detected for the samples doped with the highest erbium contents when annealed at high temperatures.     

Dependence of La2O3 content on the nonlinear electrical behaviour of ZnO, CoO and Ta2O5 doped SnO2 varistors

The effects of La₂O₃ on the properties of (Zn, Co, Ta) doped SnO₂ varistors were investigated in this study. The samples with different La₂O₃ concentrations were sintered at 1400 °C for 2 h and their properties were characterized by XRD, SEM, I-V and impedance spectroscopy. The grain size was found to decrease from 13 μm to 9 μm with increasing La₂O₃ content. The addition of rare earth element leads to increase the nonlinear coefficient and the breakdown voltage. The enhancement was expected to arise from the possible segregation of lanthanide ion due to its larger ionic radius to the grain boundaries, thereby modifying its electrical characteristics. Furthermore, the dopants such as La may help in the adsorption of O′ to O″ at the grain boundaries characteristics.     

Phase diagrams of the systems Al2O3-ZrO2-Ln(Y)2O3 as a source of multiphase eutectics for creating composite structural and functional materials

Phase equilibria in the ternary systems Al₂O₃-ZrO₂-Ln₂O₃ (Ln = La, Nd, Sm, Gd, Er, Yb and Y) were investigated by identical methods in all range of concentrations and 1250-2700 °C temperature range using differential and derivative in solar furnace thermal analysis in controlled medias, X-ray diffraction phase analysis, local X-ray spectral analysis, chemical analysis, electron and optical microscopy, petrography. The phase diagrams of the systems studied are presented as isothermal at 1650 °C sections and melting diagrams. The interaction in the systems is characterized by the absence of ternary compounds and regions of appreciable solid solutions based on the binary compounds and components. Only narrow regions of ternary solid solutions were discovered at high temperatures by CALPHAD method and because of existing small solubility on the base of ZrO₂ in the binary bounding system Al₂O₃-ZrO₂. The phase equilibria in the systems are determined by zirconia as the most stable compound. Solidification in the systems is completed in eutectic reactions. The established interaction regularities allowed to forecast interaction and phase diagrams construction in systems with other lanthanides (Ce, Pr, Pm, Eu, Tb, Dy, Ho, Tm, Lu). New 13 quasibinary and 26 ternary eutectics were found for the first time. Their temperatures rise from 1660 °C for the La₂O₃ system to 1840 °C for the Lu₂O₃ system. Fluorite-type phases equilibrate with garnet-type phases for the systems from Tb₂O₃ to Lu₂O₃. In the systems from Pr₂O₃ to Gd₂O₃ they equilibrate with perovskite-type phases and β-Al₂O₃. On the base of microstructure investigations it was established that three-phase alumina-rich eutectics crystallizes according to the mechanism of cooperative growth. It opens up possibilities to obtain composite materials using directional solidification method.     

Solvent Extraction of Lanthanides(III) with N‐Cinnamoyl‐N‐phenylhydroxylamine and Its Trifluoromethyl Derivative

Abstract

N‐m‐Trifluoromethylcinnamoyl‐N‐phenylhydroxylamine (CF₃‐CPHA) was synthesized. The acid‐dissociation constant and distribution constant between chloroform and water of CF₃‐CPHA and N‐cinnamoyl‐N‐phenylhydroxylamine (CPHA), which was the mother compound of CF₃‐CPHA, were determined spectrophotometrically. The extraction behavior of tervalent lanthanides (Ln), Pr, Eu, and Yb into chloroform solution containing CPHA or CF₃‐CPHA was studied. They are extracted as self‐adduct chelates, LnL₃(HL)₃, where L and HL denote the ligand anion and neutral ligand, respectively. The extraction constants and separation factors for the lanthanides with CPHA and CF₃‐CPHA were evaluated. The extraction constant with CPHA are smaller than that obtained with CF₃‐CPHA. However, it is observed that CPHA possesses higher selectivity than CF₃‐CPHA.     

Crystal field analysis of EuCl3.6H2O

Absorption and magnetic circular dichroism (MCD) spectra of polycrystalline EuCl₃.6H₂O samples were recorded between 16 000 and 36 000 cm⁻¹ at ambient temperature and at 77 K. A total of 104 crystal field transitions has been observed in the spectra. The MCD spectrum resembles the first derivative of the absorption spectrum, indicating the presence of (pseudo) A-terms. The advantage of MCD is the possibility of detecting quasi-degenerate crystal field levels, which are not resolved in the absorption spectrum. The coordination polyhedron around Eu³⁺ is a distorted square antiprism (C.N.=8). In order to make the crystal field calculations more tractable, the real C₂ symmetry of the europium site is approximated by a C_2v symmetry. The energy levels of the 4f⁶ configuration of Eu³⁺ are parametrized in terms of 20 free ion parameters and 9 B_q^k crystal field parameters. J-mixing is taken into account.     

Mechanism of the electrochemical deposition of samarium-based coatings

Samarium-based films have been shown to form from aqueous solutions on the surfaces of metallic substrates such as steel or aluminum, and their presence has been reported to decrease substantially the corresponding corrosion rate of the underlying metallic substrate. Based on previous reports on the deposition of oxides or hydroxides of the closely related element cerium, this work demonstrates that samarium films are formed following a similar mechanism, which involves as the fundamental step an increase in interfacial pH resulting from cathodic oxygen-reduction or hydrogen-evolution reactions. With cyclic voltammetry (CV), electrochemical quartz-crystal microbalance (EQCM) measurements, rotating-disk electrode (RDE) tests, and surface characterization techniques, namely, scanning electron microscopy (SEM) and X-ray surface microanalysis (EDX), the postulated mechanism was verified, and the surface morphology of the resulting films was correlated with the nature of the reduction reaction that triggers film formation.