Papers by Keyword: Lanthanides

Abstract: Electron trapping materials SrSO₄:Eu²⁺ were prepared by hydrothermal method from fatty alcohol polyoxyethylene (3) ether (AEO-3) aqueous solution at 200 °C for 20 h. The phase structure, microstructure and optical properties were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and excitation-emission spectroscopy (PL-PLE), respectively.

Abstract: Dyes are a source of serious pollutants from different industrial outlets and show a major contribution in polluting the environment. In the present study two dyes namely Orange G and Acid Blue 113 were compared for their photodegradation efficiency employing rare earth nanometal oxide as a visible active photocatalyst. The prepared catalyst was nanocrystalline form with particle size 70 nm and the surface of the catalyst was highly porous and rough which facilitates the absorption of the dye further enhance the photo degradation which were confirmed by various characterization techniques. Effect of pH, variation of catalyst dosage, variation of initial dye concentration and kinetic studies were conducted for both the dyes. The reaction followed a pseudo first order kinetics. The activity of the prepared catalyst was higher when compared to a commercially used metal oxide. Reusability studies proved that the catalyst prepared was very active even upto the third cycle. The degradation process was initiated by the attack of the OH radical generated in the in-situ process via visible light irradiation. EPR spin trapping technique was employed to confirm the presence of OH radicals. The prepared catalyst degraded the dye molecules of interest in lesser time duration by absorption of visible light, thereby reducing the cost of photodegradation.

Abstract: A number of newly Ln-N bond valence parameters were quantitatively estimated, which allowed us to obtain all Ln-N bond lengths with different coordination numbers in metal organic complexes. Twenty linear correlations among the mean bond valence parameters of Ln-O, Ln-N, Ln-S, Ln-Cl and Ln-C bonds of metal organic complexes have been well established and denoted by a set of linearity equations, which provides us a useful method to determine the bond valence parameters of other type Ln-atom bonds in coordination chemistry. The present work shows us a novel approach to deeply understand the chemical bonding characteristics between Ln and the ligands in various metal organic complexes.

Abstract: A series of new coordination polymers based on p-tert-butylcalix[4]arene- tetracarboxylic acid with Eu3+ (1a), Tb3+ (1b) and Tm3+ (1c) were prepared by hydro and solvothermal methods. The obtained solid compounds were characterized by infrared and luminescence spectroscopy, powder X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. The infrared curves and the x-ray diffraction patterns indicate that the same crystalline structure was obtained for all lanthanides.

Abstract: This paper elucidates the structural and electrical properties of Bi₄Ti₃O₁₂ (BIT), Bi_3.25Nd_0.75Ti₃O₁₂ (BNT075) and Bi_3.25La_0.75Ti₃O₁₂ (BLT075) compounds that were primarily prepared by a novel combustion route at temperature as low as 300°C. Single crystalline phase of bismuth-layered perovskite structure was obtained directly after combustion without calcination. X-ray diffraction and Raman spectra analysis showed the phase transition from orthorhombic to tetragonal symmetry with substituting compounds. Compared to BIT, the Curie temperature at maximum dielectric peak of BNT075 and BLT075 decreased to lower values of 434°C and 365°C, respectively. The loss tangen for corresponding substitution compounds were 5 times lower than that of BIT. Besides, BNT075 resulted in large remanent polarization (2P_r) and coercive field (E_c) values of 19µC/cm² and 45kV/cm, respectively, while 17.6µC/cm² and 42kV/cm for BLT075.

Abstract: One of the interests on the study of doped materials with rare earths in their bulk or nanoscale size is owing to the enhancement of the intensity of light in their photoluminescence when a lanthanide exists in a receptor material, as ZnO in our case. Until now, one of the most useful theories for calculations of electronic properties in molecular and solid state systems is the Density Functional Theory (DFT), which is not capable to manage well the presence of high localized electrons, as in lanthanide compounds in general and the doped case in particular. We propose to study these materials with super cell model using some correction to the standard calculations. For this goal, we employ the WIEN2k [1] code using the LDA+U approximation to take into account the strong correlation of the f electrons coming from the lanthanide. We emphasise the study of deformation due to the presence of Eu ion in the structure of host material, optimizing the position of neighboring Oxygen atoms. This deformation has been related to Kondo Resonance [2] appearing around the Fermi Energy of the compound, due to hybridization [3] among the f electrons from rare earth and neighboring oxygen levels.

Abstract: In Lead-cadmium fluorogermanate glasses (PbF2-CdF2-PbGeO3) the addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (Tg) and to an enhancement of the ionic conductivity properties. Based on different spectroscopic techniques (19F NMR, Ge K-edge X-ryas absorption and Raman scattering) an heterogeneous glass structure is proposed at the molecular scale, which can be described by fluoride rich regions permeating the metagermanate chains. The temperature dependence of the 19F NMR lineshapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluoride mobility in these systems. Eu3+ emission and vibronic spectra are used to follow the crystallization process leading to transparent glass ceramics.

Abstract: New lanthanotungstocobaltates with the Keggin structure and general formula KxHy[Ln(CoW11O39)(H2O)3]⋅nH2O or KxHyLn[Ln(CoW11O39)(H2O)3]⋅nH2O, LnIII = Ce, La, Eu, Sm, Tb, were prepared and characterized for the first time. Hybrid silica materials, with the polyoxoanions anchored to spherical silica particles, were also prepared and characterised. Their study by IR spectroscopy and EDS suggested that the structure of the Keggin-type polyanions is maintained when they are immobilized in the silica material.

Abstract: Effects of the rare-earth additives (RE = Sc, Y, La, Nd, Gd, Sm, Yb and Lu) and nitrogen on contact strength of the oxide and oxynitride glasses were investigated at room temperature. The advantage of this relatively new technique is its experimental simplicity and using of miniature samples, however, a relatively complex stress distribution around the contact points reduces Weibull parameter in comparison with the conventional bending strength. Contact strength of the tested glasses is also strongly influenced by surface finish. The differences in the effects of REmodifiers in oxide and oxynitride glasses suggest that the contributions from RE and nitrogen may not be simply additive, as observed earlier for various thermo-mechanical properties. However, additional study is necessary to eliminate the effects of surface defects to support this assumption.