Papers by Keyword: Rare-Earth Ions

Abstract: In this study, the main thermal, structural and mechanical properties of optical glass materials were investigated by conventional glass melting method. The thermal properties of optical glass materials are important in that they constitute the first steps towards the investigation of other physical and chemical properties. According to the thermal properties of the material, the glass transition temperature, T_g, increases for different glass compositions. The XRD, XRF, FT-IR and hardness properties of the obtained optical glass materials were determined experimentally in terms of their structural and mechanical properties for their suitability for potential applications. XRD spectra obtained without heat treatment of glass materials show that the material structure is amorphous. In the same way, Vicker’s hardness values of the glassware increase relative to the different glass compositions, resulting in a result that the material is influenced by the bonds between the constituents of the chemical components.

Abstract: The magnetization processes of HoAl₃(BO₃)₄ rare-earth aluminum borates have been studied theoretically. Magnetic properties of the crystals were examined. The dependencies of the magnetic susceptibility on the magnitude and direction of magnetic field were calculated. Study of a magnetoelectric effect was performed and the dependencies of the polarization on the strength and orientation of a magnetic field and temperature were obtained. A comparison of the theoretical and experimental data was performed, their consistency has been ascertained.

Abstract: The SrSO₄ spherical aggregates with hierarchical architecture was fabricated by using Sr(NO₃)₂ react with Na₂SO₄ aqueous solution under ambient conditions at room temperature. The SrSO₄ spherical aggregates have a uniform diameter of about 10μm, which are composed of numerous well-aligned single tablet-like SrSO₄ crystalline oriented radially to their centre. The phase structure, microstructure and luminescence properties were characterized by XRD, SEM, PL and DRS, respectively.

Abstract: The main crystallization trends of rare-earth complex oxides from alkaline phosphate-molybdate (tungstate) melts have been studied in a light of structure - luminescence properties relationships. The regions of formation MI3RE(PO4)2, REPO4 and M^I₂RE(PO₄)(M^VIO₄) from self flux systems M^I–P–RE–O (M^I–alkaline metal; M^VI–Mo, W) have been defined. The influence of MI/MVI ratio in the initial melt has been shown to play the key role in solid phase formation and structural peculiarities of REO_x polyhedral condensation of compounds obtained.

Abstract: Rare-earth (RE)-doped TiO₂ photocatalysts were prepared by doping samarium ions into TiO₂ nanoparticles in a sol-gel process. The samples were characterized using X-ray diffraction (XRD). Their photocatalytic activities were evaluated by photodegradation of methyl orange (MO) in water under UV light irradiation. Finally, influences of rare-earth ions doping on the structure and photocatalytic activity of TiO₂ were studied using grey correlation analysis method based on multi-variable grey model. The experimental results indicated that the doping modifications of TiO₂ work through the structure change in nanoscale, leading to the change of activities. It was also found that the main actors influencing on activity of RE-doped TiO₂ are crystalline size (D) and crystal constant (a) for the MO photodegradation base on the grey relational analysis method. Using the same method above, the activities of RE-doped TiO₂ photocatalysts could be predicted and doping concentration need to be optimized.

Abstract: A wet non-conventional method for preparing aluminophosphate glasses is presented. Aluminophosphate glasses belonging to the oxide system Li2O-BaO-Al2O3-La2O3-P2O5, doped with rare-earth ions (Pr3+, Er3+, Gd3+, and Yb3+) were obtained. The influence of the doping ions on the optical properties of the phosphate glasses has been investigated in relation with micro-structural and local electronic phenomena The optical behavior of Li2O-BaO-Al2O3-La2O3-P2O5 glasses doped with 3% mol. rare-earth ions has been studied by ultra-violet-visible-near-infra-red (UV-VISNIR) spectroscopy. The transmission spectra revealed electronic transitions between 4f and 6s inner orbital of the rare-earth ions. Structural information via optical phonons was provided by infra-red (IR) absorption spectra in the range 400-4000 cm-1. IR optical phonons are characteristic for the vitreous phosphate network, showing out the glass network-forming role of P2O5. The absorption spectra present the main PO2 and P-O-P symmetrical stretch modes besides P-O-P bend mode, P-OH, P=O, PO3 2-, asymmetrical and symmetrical vibration modes. Fluorescence spectra of the rareearth- doped aluminophosphate glasses, in the visible range, were obtained by laser excitation at 514.5 nm. The fluorescence signals revealed specific electronic transitions, which provide visible and near-infra-red emission. Glasses containing rare-earth ions exhibit luminescence at the following wavelengths: Pr3+ ions at 820 nm and 880 nm, Er3+ ions at 520 nm, 550 nm and 560 nm, Gd3+ ions at 530 nm, 540 nm, 550 nm 820 and 880 nm, Yb3+ions at 530 nm, 540 nm, 550 nm and 980 nm.

Abstract: Microscopic elementary events responsible for magnetoplastic effect are studied in detail by means of photoluminescence, electron spin resonance and SQUID magnetometry in NaCl:Eu single crystals. The Eu2+ clusters being dislocation obstacles were used as a spin and luminescent labels allowed detecting simultaneous spin and atomic structure transitions in exchange-coupled few-atomic Eu2+ clusters under static magnetic field B = 5 T. Rearrangement of atomic structure of these clusters changes the lattice distortions around them and effectiveness of clusters interaction with moving dislocations during plastic flow. From the comparison of spectroscopic data and numerical calculations of aggregation pathways of small clusters it was concluded that magnetosensitive clusters contain two Eu2+ ions with parallel spins (dimers). Two different ways of creating of magnetosensitive dimers in the crystal lattice are found: (1) slow diffusion limited aggregation in freshly quenched crystals, and (2) fast aggregation stimulated by dislocations dynamical distortions of lattice provided by the plastic deformation of aged crystals.

Abstract: The SiC powder of median size 0.8 µm was mixed with polyacrylic acid (PAA, dispersant) in a 0.3 M-R(NO3)3 solution (R=Yb, Y, Gd, Sm, Nd and La) at pH 5 to adsorb uniformly the sintering additive (R3+ ion) on the SiC surface. The addition of PAA to the SiC suspension with R3+ ion increased the amount of R3+ ion fixed to SiC particles. The aqueous 30 vol% SiC suspension with 0.52 mass% PAA and 1.50 mass% R2O3 (as R3+ ion) against the mass of SiC, was consolidated by filtration through a gypsum mold to form green compacts of 50-52 % of theoretical density. The consolidated green compacts were hot–pressed under a pressure of 39 MPa at 1950°C for 2 h in an Ar flow. The green compacts were densified with grain growth to 76 - 99 % relative density. The addition of smaller R3+ ion was effective to enhance the sinterability of SiC and also to achieve smaller grain size of SiC. The sintering mechanisms were discussed based on the analysis of the shrinkage curves of SiC/R2O3 compacts during the hot-pressing.