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Rare Earth (rare + earth)
Terms modified by Rare Earth Selected AbstractsComparative Electrochemical Study of Unsubstituted and Substituted Bis(phthalocyaninato) Rare Earth(III) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2004Peihua Zhu Abstract The electrochemistry of homoleptic substituted phthalocyaninato rare earth double-decker complexes M(TBPc)2 and M(OOPc)2 [M = Y, La...Lu except Pm; H2TBPc = 3(4),12(13),21(22),30(31)-tetra- tert -butylphthalocyanine, H2OOPc = 3,4,12,13,21,22,30,31-octakis(octyloxy)phthalocyanine] has been comparatively studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in CH2Cl2 containing 0.1 M tetra- n -butylammonium perchlorate (TBAP). Two quasi-reversible one-electron oxidations and three or four quasi-reversible one-electron reductions have been revealed for these neutral double-deckers of two series of substituted complexes, respectively. For comparison, unsubstituted bis(phthalocyaninato) rare earth analogues M(Pc)2 (M = Y, La...Lu except Pm; H2Pc = phthalocyanine) have also been electrochemically investigated. Two quasi-reversible one-electron oxidations and up to five quasi-reversible one-electron reductions have been revealed for these neutral double-decker compounds. The three bis(phthalocyaninato)cerium compounds display one cerium-centered redox wave between the first ligand-based oxidation and reduction. The half-wave potentials of the first and second oxidations and first reduction for double-deckers of the tervalent rare earths depend on the size of the metal center. The difference between the redox potentials of the second and third reductions for MIII(Pc)2, which represents the potential difference between the first oxidation and first reduction of [MIII(Pc)2],, lies in the range 1.08,1.37 V and also gradually diminishes along with the lanthanide contraction, indicating enhanced ,,, interactions in the double-deckers connected by the smaller, lanthanides. This corresponds well with the red-shift of the lowest energy band observed in the electronic absorption spectra of reduced double-decker [MIII(Pc,)2], (Pc, = Pc, TBPc, OOPc). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Hydrothermal Synthesis of Rare Earth (Tb, Y) Hydroxide and Oxide Nanotubes,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2003Y.-P. Fang Abstract In this paper, Tb(OH)3 and Y(OH)3 single-crystalline nanotubes with outer diameters of 30,260,nm, inner diameters of 15,120,nm, and lengths of up to several micrometers were synthesized on a large scale by hydrothermal treatment of the corresponding oxides in the presence of alkali. In addition, Tb4O7 and Y2O3 nanotubes can be obtained by calcination of Tb(OH)3 and Y(OH)3 nanotubes at 450,°C. X-ray diffraction (XRD), field-emission scanning electron microscopy, transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry, and differential scanning calorimetry (DSC) have been employed to characterize these nanotube materials. The growth mechanism of rare earth hydroxide nanotubes can be explained well by the highly anisotropic crystal structure of rare earth hydroxides. These new types of rare earth compound nanotubes with open ends have uses in a variety of promising applications such as luminescent devices, magnets, catalysts, and other functional materials. Advantages of this method for easily realizing large-scale production include that it is a simple and unique one-pot synthetic process without the need for a catalysts or template, is low cost, has high yield, and the raw materials are readily available. The present study has enlarged the family of nanotubes available, and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials. [source] Effect of Heat Treatment on Far Infrared Emission Properties of Tourmaline Powders Modified with a Rare EarthJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Dongbin Zhu Far infrared materials were prepared by precipitation method using natural tourmaline (XY3Z6Si6O18(BO3)3W4, where X is Na+, Ca2+, K+, or vacancy; Y is Mg2+, Fe2+, Mn2+, Al3+, Fe3+, Mn3+, Cr3+, Ti4+ or Li+; Z is Al3+, V3+, Cr3+, or Mg2+; and W is OH,, F,, or O2,) powders and cerium nitrate as raw materials. The results of Fourier transform infrared spectroscopy (FTIR) show that rare earth Ce can enhance the far infrared emission properties of tourmaline. Through characterization by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the mechanism by which rare earth Ce acts on the far infrared emission property of tourmaline was systematically studied. The XPS spectra show that the Fe3+ ratio inside tourmaline powders after heat treatment can be raised by doping Ce. Moreover, it is showed that Ce3+ is dominant inside the samples but its dominance is replaced by Ce4+ outside. In addition, XRD results indicate the formation of CeO2 crystallites during the heat treatment and further TEM observations show they exist as nanoparticles on the surface of tourmaline powders. Based on these results, we attribute the improved far infrared emission properties of Ce-doped tourmaline to the enhanced unit cell shrinkage of the tourmaline arisen from the oxidation of Fe2+ (0.074 nm in radius) to Fe3+ (0.064 nm in radius) inside the tourmaline caused by the redox shift between Ce4+ and Ce3+. [source] Books and Multimedia ReviewsMETEORITICS & PLANETARY SCIENCE, Issue 3 2001Article first published online: 4 FEB 2010 Book reviewed in this article: Catalogue of Meteorites, Fifth Edition (Revised and Enlarged) by Monica M. Grady Extrasolar Planets: The Search for New Worlds by Stuart Clark The Moon: Resources, Future Development and Colonization by David Schrunk, Burton Sharpe, Bonnie Cooper and Madhu Thangavelu Rare Earth: Why Complex Life is Uncommon in the Universe by Peter D. Ward and Donald E. Brownlee [source] Rare Earth, Major and Trace Elements in the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, JapanRESOURCE GEOLOGY, Issue 4 2005Yasuhiro Kato Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today. [source] ChemInform Abstract: New A2/3-xRh2O4 Compounds with the CaFe2O4 Structure Where A Is a Rare Earth or Bi.CHEMINFORM, Issue 12 2009Hiroshi Mizoguchi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Ternary Rare Earth and Actinoid Transition Metal Carbides Viewed as Carbometalates.CHEMINFORM, Issue 51 2007Enkhtsetseg Dashjav Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Some Ternary Oxyborates of the Na2O,M2O3,B2O3 (M: Rare Earth or Aluminum) Systems: Synthesis, Structure and Crystal Growth.CHEMINFORM, Issue 49 2006P. Peshev Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis and Crystal Structure of (Ca,Ln)(Mn,Ti)O3 (Ln: Rare Earth).CHEMINFORM, Issue 22 2006Migaku Kobayashi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Aldol Condensations of Aldehydes and Ketones Catalyzed by Rare Earth(III) Perfluorooctane Sulfonates in Fluorous Solvents.CHEMINFORM, Issue 15 2006Wen-Bin Yi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Solid-State and Solution Studies of {Lnn(SiW11O39)} Polyoxoanions: An Example of Building Block Condensation Dependent on the Nature of the Rare Earth.CHEMINFORM, Issue 24 2003Pierre Mialane Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Synthesis and Magnetic Properties of ALnO2 (A: Cu or Ag; Ln: Rare Earths) with the Delafossite Structure.CHEMINFORM, Issue 45 2009Naoyuki Miyasaka Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Magnetic Properties of EuLn2O4 (Ln: Rare Earths).CHEMINFORM, Issue 40 2009Keiichi Hirose Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Magnetic Properties of Orthorhombic Fluorite-Telated Oxides Ln3SbO7 (Ln: Rare Earths).CHEMINFORM, Issue 40 2009Yukio Hinatsu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Electrical and Magnetic Properties of LnOZnPn (Ln: Rare Earths; Pn: P, As, Sb).CHEMINFORM, Issue 19 2008Yoshiki Takano Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Hydrogen Absorption Kinetics and Mechanisms of Rare Earths (La, Ce, Pr, Nd, Tb, Dy) in the H2O Surface Reaction at Room Temperature.CHEMINFORM, Issue 19 2006Hirohisa Uchida Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Crystal Structure and Electrical Properties of the New Ln2MSi2 Compounds (Ln: Rare Earths; M: Fe, Co).CHEMINFORM, Issue 31 2004F. Merlo Abstract For Abstract see ChemInform Abstract in Full Text. [source] Comparison of the surface and catalytic properties of rare earth-promoted CaO catalysts in the oxidative coupling of methaneJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2006Vilas H Rane Abstract Rare earth (viz. La, Ce, Sm, Nd and Yb) promoted CaO catalysts have been investigated, comparing their surface properties (viz. surface area and basicity/base strength distribution) and catalytic activity/selectivity in the oxidative coupling of methane at different reaction conditions (temperatures, 650,800 °C, CH4/O2 ratios, 2.0,8.0 and space velocity, 51 360 cm3 g,1 h,1). The surface properties and catalytic activity/selectivity are strongly influenced by the rare earth promoter and its concentration. Apart from the Sm-promoted CaO catalyst, both the total and strong basic sites (measured in terms of CO2 chemisorbed at 50° and 500 °C respectively) are decreased due to the promotion of CaO by rare earth metals (viz. La, Ce, Nd and Yb). The catalytic activity/selectivity is strongly influenced by the temperature, particularly below ,700 °C, whereas at higher temperature no further effect is seen. The La2O3CaO, Nd2O3CaO and Yb2O3CaO catalysts showed high activity and selectivity, and also their results are comparable. Among the catalysts, Nd-promoted CaO (with Nd/Ca = 0.05) showed the best performance (19.5% CH4 conversion with 70.8% C2+ selectivity) in the oxidative coupling of methane. A close relationship between the surface density of total and strong basic sites (measured in terms of CO2 chemisorbed at 50° and 500 °C respectively) and the C2+ selectivity and/or C2+ yield has been observed. Copyright © 2005 Society of Chemical Industry [source] Rare Earth, Major and Trace Elements in the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, JapanRESOURCE GEOLOGY, Issue 4 2005Yasuhiro Kato Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today. [source] Synthesis and Characterization of Poly(butylene adipate- co - terephthalate) Catalyzed by Rare Earth StearatesCHINESE JOURNAL OF CHEMISTRY, Issue 10 2007Kui ZHU Abstract Rare earth (Nd, Y, La, Dy) stearates have been synthesized and used as single component catalysts for the polycondensation of dimethyl terephthalate, adipic acid and 1,4-butanediol for the first time preparing biodegradable poly(butylene adipate- co -terephthalate) (PBAT) with high molecular weight. The microstructures of PBAT were characterized by 1H NMR spectra. The PBAT exhibits good mechanical properties such as high tensile strength (ca. 20 MPa) and long break elongation (>700%). [source] Study on syntheses and anticoagulant action of heparin/rare earth nano-oxides hybrid material,BIOPOLYMERS, Issue 10 2010Kun-Jie Wang Abstract Four hybrid materials of RE2O3 -TDI-Heparin (TDI = Toluene 2,4,diisocyanate, RE = La, Eu, Nd, Sc) were prepared by the method of graft. The materials were characterized by IR, TG, and SEM, which confirmed that the heparin was grafted on the surface of TDI modified rare earth nano-oxides. The cell adhesion experiment and the anticoagulant experiment demonstrated that the materials have lower cell toxicity, better cell adhesion as well as better anticoagulant action. In addition, the clotting time of hybrid materials were shortened compared with the heparin. © 2010 Wiley Periodicals, Inc. Biopolymers 93: 887,892, 2010. [source] Growth of single-grain GdBa2Cu3O7-x superconductors by top seeded infiltration and growth techniqueCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2010Guo-Zheng Li Abstract The top seeded infiltration and growth technique (TSIG) is an effective way for the preparation of bulk REBa2Cu3O7-x (RE-123, where RE denotes rare earth) with finely dispersed RE2BaCuO5 (RE-211) particles compared to the conventional melt growth (MG) method. The nucleation temperature and the ending growth temperature are the most important parameters need to be optimized during the preparation of RE-123 bulks by the TSIG process. In this paper, the effects of these parameters on the growth of single-grain GdBa2Cu3O7-x (GdBCO) superconductors have been investigated experimentally. It is found that the temperature for the growth of single-grain GdBCO is in the region between 1040 °C and 1015 °C. In addition, the relation between growth rate and supercooling has been investigated in detail. The combined techniques of SEM and EDS were used to study the microstructure of the samples grown at different temperatures. Based on this, a two-step slow cooling method during the crystallization process is proposed for the fabrication of RE-123 bulks. Finally, the single-grain GdBCO samples of the diameters 20 mm and 30 mm were fabricated successfully by the TSIG technique, with the slow-cooling process in the temperature window 1030 °C,1020 °C for 60 h and 100 h respectively. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal growth features and properties of layered rare earth and barium cobaltatesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005G. L. Bychkov Abstract High quality single crystals of LnBaCo2O5+, (0 < , < 1) (Ln = Pr, Eu, Gd, Tb, Dy) with rectangular shape and average dimensions 5 mm × 5 mm × 1 mm were grown for the first time from overstoichiometric flux melt. The data on the primary crystallization field of most cobaltate phases, which appear in parts of corresponding Gibbs triangles in the range 1373 , 1523 K are discussed. Bulk single crystals of new phases HoBaCo4O7 up to 300 mm3, YBaCo4O7 and TbBaCo4O7 up to 10 mm3 in volume were grown first. A solution of these compounds structure has been found in the space group P63mc. For the Ln = Pr, Gd, Sm, Tb, Dy, Ho based systems under the liquidus line there are several other new cobaltate phases of both perovskite, and hexagonal crystal structure. Stability of the double perovskite phase and temperature of the antiferromagnetic , ferromagnetic phase transition in relation to the radius of rare earth ions are compared. The data on the exact analysis of chemical composition, including EDX and iodometric titration, as well as results on magnetic susceptibility of EuBaCo1- xAlxO5+, (0 < x < 0.3) are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthesis and Characterization of Mixed Phthalocyaninato and meso -Tetrakis(4-chlorophenyl)porphyrinato Triple-Decker Complexes , Revealing the Origin of Their Electronic AbsorptionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004Xuan Sun Abstract Two series of mixed phthalocyaninato and porphyrinato rare earth(III) triple-decker complexes [M2(Pc)(TClPP)2] (1a,10a) and [M2(Pc)2(TClPP)] (1b,11b) [M = Y, La,Er except Ce and Pm; Pc = phthalocyaninate; TClPP = tetrakis(4-chlorophenyl)porphyrinate] have been prepared by treating the half-sandwich complexes [M(TClPP)(acac)] (acac = acetylacetonate), generated in situ from [M(acac)3]·nH2O and H2(TClPP), with Li2(Pc). All the triple-decker complexes have been characterized by a wide range of spectroscopic and electrochemical methods. The molecular structures of [M2(Pc)(TClPP)2] (M = Y, Ho) have also been determined, and show a symmetrical disposition of ligands, with two outer domed TClPP and one inner Pc rings. A systematic investigation of the optical and electrochemical data of these complexes has revealed the nature of the HOMO and LUMO, as well as the origin of the electronic absorptions of these triple-decker complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Hydrothermal Synthesis of Rare Earth (Tb, Y) Hydroxide and Oxide Nanotubes,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2003Y.-P. Fang Abstract In this paper, Tb(OH)3 and Y(OH)3 single-crystalline nanotubes with outer diameters of 30,260,nm, inner diameters of 15,120,nm, and lengths of up to several micrometers were synthesized on a large scale by hydrothermal treatment of the corresponding oxides in the presence of alkali. In addition, Tb4O7 and Y2O3 nanotubes can be obtained by calcination of Tb(OH)3 and Y(OH)3 nanotubes at 450,°C. X-ray diffraction (XRD), field-emission scanning electron microscopy, transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray spectroscopy (EDS), thermogravimetry, and differential scanning calorimetry (DSC) have been employed to characterize these nanotube materials. The growth mechanism of rare earth hydroxide nanotubes can be explained well by the highly anisotropic crystal structure of rare earth hydroxides. These new types of rare earth compound nanotubes with open ends have uses in a variety of promising applications such as luminescent devices, magnets, catalysts, and other functional materials. Advantages of this method for easily realizing large-scale production include that it is a simple and unique one-pot synthetic process without the need for a catalysts or template, is low cost, has high yield, and the raw materials are readily available. The present study has enlarged the family of nanotubes available, and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials. [source] Raman phonons and Raman Jahn,Teller bands in perovskite-like manganitesJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2001Milko N. Iliev The perovskite-like manganites R1,xAxMnO3, where R is a trivalent rare earth or Y and A is a divalent alkaline earth element, are characterized by a strong interplay of magnetism, electric transport and crystallographic distortion. At doping levels 0.15 < x < 0.45 the materials exhibit colossal magnetoresistance near the concomitant ferromagnetic and insulator,metal transitions. At a fractional doping level, such as x = 0.5, the crystallographic and magnetic environment is strongly modified and charge ordering between Mn3+ and Mn4+ or phase separation takes place. In this work, the polarized Raman spectra of the orthorhombic and rhombohedral phases of parent RMnO3 compound were analyzed in close comparison with results of lattice dynamic calculations. We argue that the strong high-wavenumber bands between 400 and 700 cm,1, which dominate the Raman spectra of rhombohedral RMnO3 and magnetoresistive La1,xAxMnO3 are not proper Raman modes for the R3c or Pnma structures. Rather, the bands are of phonon density-of-states origin and correspond to oxygen phonon branches activated by the non-coherent Jahn,Teller distortions of the Mn3+O6 octahedra. The reduction of these bands upon doping of La1,xAxMnO3 and their disappearance in the ferromagnetic metallic phase support the model. The variation with temperature of the Raman spectra of La0.5Ca0.5MnO3 is also discussed. The results give a strong indication for charge and orbital ordering and formation of superstructure at low temperatures. Copyright © 2001 John Wiley & Sons, Ltd. [source] Experimental Design Applied to Silicon Carbide SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2003Juliana Marchi Silicon carbide is a promising structural ceramic used as abrasives and applied in metallurgical components, due to its low density, high hardness, and excellent mechanical properties. The composition and content of the additive can control liquid-phase sintering of SiC. Compositions based on the SiO2,Al2O3,RE2O3 system (RE = rare earth) have been largely used to promote silicon carbide densification, but most studies are not systematically presented. The aim of this work is to study the effect of several oxide additives in the SiO2,Al2O3,Y2O3 system on the densification of silicon carbide using experimental design. This technique seems to be effective in optimizing the values of maximum density with minimum weight loss. [source] Rare earth ions in porous silicon: optical propertiesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007H. Elhouichet Abstract Porous silicon (PS) is doped with rare earth (RE) ions (Er, Eu, Tb) by electrochemical anodisation. The penetration of RE into the PS layer is confirmed by Rutherford Backscattering Spectroscopy (RBS) and by Energy Dispersive X-ray (EDX) measurements. Efficient visible and infrared emissions were observed at room temperature. The activation temperatures of Eu, Tb and Er in PS are determined from the effect of thermal annealing on the photoluminescence (PL) intensity. From the evolution of the PL intensity versus temperature, it was found that a RE related level defect can be involved on the excitation and emission processes. Pump intensity dependent PL studies revealed that for the electrochemical incorporation, most of the RE ions are localized inside the Si nanocrystallites and not in stochiometric SiO2. The optical cross section is close to that of erbium in Si nanocrystallites. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electronic structure of TbBa2Cu3O7PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2010Maciej, uszczek Abstract The full-potential linearized augmented plane wave (FP-LAPW) method was used for spin-polarized electronic structure calculations of stoichiometric TbBa2Cu3O7 (Tb123), not synthesized as a single phase yet. The generalized gradient approximation plus Hubbard correction (GGA,+,U) was employed for Tb4f electrons to prevented fractional occupation of states at Fermi level and hybridization with other electrons. The determined band structure is Y123-like with the metallic character as in the other superconducting R123 (R,=,rare earth). The presented results indicate that strong on-site spin moment of Tb could not effectively influence the neighbours and the induced magnetic interactions in the system are weak (CuO planes) or negligible (BaO planes and CuO chains). This appears to be the repercussion of the ,size effect' due to relatively small Tb+3 ionic radius. The predicted weak influence of magnetic moments of Tb on CuO states in the assumed (hypothetical) Fermi liquid phase of TbBa2Cu3O7 could favour the rise of superconductivity in this system. [source] Thermal quenching of luminescence and isovalent trap model for rare-earth-ion-doped AlNPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007H. J. Lozykowski Abstract Investigations of the luminescent properties of Pr-, Eu-, Tb- and Tm-implanted AlN thin films at temperature in the range 9,830 K are reported. The temperature studies of photoluminescence and cathodoluminescence spectra revealed unexpectedly weak thermal quenching for all investigated rare earth (RE) ions. The maximum CL emission is observed from Eu (red) at 485 K, Tb (green) at 590 K and Tm (blue) at 530 K, respectively. For Tb- and Tm-doped AlN samples, temperature-dependent crossrelaxation processes were observed. Photoluminescence excitation spectra, obtained under UV excitation in the spectral range 200,400 nm, exhibit several bands. It is proposed that the RE ions exist in semiconductors as isolated ions (singlet), nearest-neighbor (nn) ion pairs (dimer), and three ions (trimer). The Koster,Slater and simple spherical potential-well models for RE-structured isovalent (RESI) hole trap are proposed. The exciton binding energies of RESI traps are calculated and compared with experimental thermal-quenching energies. The energy-transfer processes between the AlN host and the 4f-shell systems are emphasized as the main mechanisms for thermal-quenching processes rather than nonradiative decay of 4f transitions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||