- Synthesis and characterization of mixed fluorides Y1-xCa2+1.5xF7 (-1.33 ≤ x ≤ 1.0)
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In this paper, we report on the synthesis and characterization of the Y1-xCa2+1.5xF7 (-1.33 ≤ x ≤ 1.0) compounds and the phase equilibria in the CaF2-YF3 system, in the continuation of our earlier studies on Sr and Ba analogues. It was found that the solubility limit of YF3 in the CaF2 lattice is about 33 mol% as compared to about 25 mol% of YF3 in BaF2 and SrF2. The CaF2-YF3 system shows the formation of an ordered cubic superstructure after the solubility limit. A hexagonal tysonite type phase separates out beyond 41 mol% of YF3. A single phasic tysonite type product was obtained at the composition with about 75 mol% of YF3, i.e., Y1.9Ca0.65F7.
- Achary,Patwe,Tyagi
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- An organically templated yttrium fluoride with a 'Super-Diamond' structure
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An organically templated yttrium fluoride has been prepared hydrothermally and characterised by X-ray powder diffraction. The crystal structure of [C3N2H12]0.5[Y3F10] may be regarded as a 'Super-Diamond' framework, space group Fdover(3, -) m, a=15.4817(1) A, where each carbon atom site of the diamond structure is replaced by a polyhedral [Y6F8F24/2]2- unit. The basic framework type is isostructural with the known phase (H3O)[Yb3F10]·H2O. The novelty in the present case lies in the use of the organic structure-directing agent 1,3-diaminopropane.
- Stephens, Nicholas F.,Lightfoot, Philip
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- The phase diagram YF3-GdF3
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The binary phase diagram YF3-GdF3 was studied by differential scanning calorimetry (DSC). Yttrium fluoride and gadolinium fluoride show complete miscibility in all three phases (orthorhombic room temperature phase, trigonal or hexagonal high temperature phase, liquid). The transformations between room temperature and high temperature phases are of first order and occur at 1338.6 K (YF3) or 1174.8 K (GdF3). Melting points are 1403.1 K (YF3) or 1525.7 K (GdF3), respectively. The cp (T) curve of GdF3 shows a λ shaped local maximum at 1333 K that might be related to a further solid phase transformation of second order.
- Klimm,Ranieri,Bertram,Baldochi
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- Phase equilibria in the system sodium fluoride-yttrium fluoride
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A phase diagram of the condensed system NaF-YF3 was constructed from data obtained in cooling-curve and quenching experiments. The number and identity of phases co-existing at equilibrium were determined by use of the X-ray diffractometer and the petrographic microscope. Two compounds, NaF-YF3 and 5NaF-9YF3, were formed from the components. Each compound exists in two polymorphic forms, the high-temperature form in both cases crystallizing from molten mixtures as fluorite-like cubic crystals. The two cubic phases form a continuous solid solution with a maximum melting temperature of 975° at the composition 5NaF-9YF3. Lattice parameters and refractive indices of the solid solution appear to be linear functions of the YF3 content, a = 5.447-5.530 A?., refractive index 1.430-1.470. Pure crystals of NaF·YF3 invert from the fluorite cubic form, on cooling below 691°, to a hexagonal form which is isostructural with β2-Na2ThF6, with lattice constants a = 5.95, c = 3.52 A?. The five primary phase fields below the liquidus were found to be NaF, hexagonal NaF·YF3, NaF·YF3-5NaF·9YF3 ss, and two forms of YF3. Two eutectics occur in association with these primary phases, at 29 and 75 mole% YF3 and at 638 and 947°, respectively. Because of the isomorphism of YF3 with the trifluorides of the rare earths samarium-lutetium and the similarity of their cation sizes, the system NaF-YF3 is predicted to be an approximate model for each of the binary systems SmF3-LuF3 with NaF.
- Thoma,Hebert,Insley,Weaver
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- Effect of the fluoride additives on the oxidation of AlN
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The oxidation of AlN powder added by the fluorides at temperatures below 700°C in air was discovered in this study. The obvious onset of oxidation of AlN with cryolite and YF3 additions is below 700°C with the product of α-Al2O3 phase, which usually occurs in single AlN powder above 1100°C. The changes on the weight and the FTIR spectra of the AlN powder fired at temperatures lower than 700°C show that cryolite and YF3 greatly promote the oxidation of AlN powder at these temperatures. Different from the action of cryolite and YF3 powder, CaF2 has no obvious effect on the oxidation of AlN. A possible oxidation process, in part corroborated by FTIR and XRF, was proposed to explain the results in the experiments. The oxidation kinetics of AlN in the presence of cryolite were also discussed at the temperatures ranging from 550 to 700°C from the data of the weight gains in this region. The result shows that the oxidation follows a linear law, which implies a reaction rate-controlled process. The considerably low activation energy of 67 kJ mol-1, which is associated with the quick oxidation and the formation of α-Al2O3 at temperatures below 700°C, was determined from the slope of the line fit.
- Zhou, Heping,Qiao, Liang,Fu, Renli
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- The Copper Ampoule: A New Reactor for the Solid-State Synthesis of Complex Lanthanide Fluorides
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For the first time, copper ampoules have been used as reactors for the solid-state synthesis of complex lanthanide fluorides under vacuum. The high ductility of copper allows for high-vacuum tight sealing of the ampoules by cold welding. Furthermore, no chemical reactivity of copper toward solid fluorides has been observed. Thus, for an examination in view of optical upconversion properties, the superstructure phases Ba4-xY3+xF17+x(x≈0.08) and Pb4?xY3±xF17±x(x≤0.2) have been synthesized by annealing of mixtures of binary fluorides in evacuated copper ampoules.
- Egger, Philipp,Peters, Nils,Hulliger, Juerg
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- Electrical and dielectric investigations of the conduction processes in KY3F10 crystals
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Dielectric constant and ac and dc electrical conductivity measurements have been performed in single crystals of the flourite compound KY3F10, in the temperature range 100 to 770 K. The dielectric response shows both dipolar and char
- Ayala,Oliveira,Gesland,Moreira
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- Hydrothermal synthesis and white luminescence of Dy3+-Doped NaYF4 microcrystals
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2 mol% Dy3+-doped NaYF4 microcrystals with different morphologies and crystalline phases have been synthesized through a hydrothermal method without assistance of any surfactant, catalyst, or template by controlling reaction temperatures, reaction time, and molar ratios of reactants. For comparison, the samples were also synthesized by a direct coprecipitation method. The final products were characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission spectra, and luminescent dynamic decay curves. Dy3+ exhibits bright white light under near ultraviolet 350 or 351 nm excitation and the white light was evaluated by chromaticity coordinates. The experimental results suggest that the obtained Dy3+-doped NaYF4 microcrystals have potential applications in white light materials.
- Cao, Chunyan,Yang, Hyun Kyoung,Chung, Jong Won,Moon, Byung Kee,Choi, Byung Chun,Jeong, Jung Hyun,Kim, Kwang Ho
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- Studies on the reaction of ammonium fluoride with lithium carbonate and yttrium oxide
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The reaction of Y2O3 and Li2CO3 with NH4F to produce LiYF4 was studied by thermogravimetric and X-ray diffraction methods. NH4F reacts easily with Li2CO3 in a one-step exothermic process. Fluorination of yttrium oxide gives first YF3 . 1.5NH3 which decomposes at 300-380°C to YF3 +NH3. This process is exothermic. In the absence of excess NH4F, an amou nt of YOF is produced, in addition to YF3, as a product of the reaction of YF3 and unreacted Y2O3. This reaction is endothermic. In the ternary system NH4F-Li2CO3-Y2O3, the first reacts separately with each of the other two and the resulting mixture of simple yttrium and lithium fluorides is converted into LiYF4 at high temperatures.
- Kowalczyk, Ewa,Diduszko, Ryszard,Kowalczyk, Zbigniew,Leszczynski, Tomasz
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- Thermodynamics of the lanthanide trifluorides. IV. The heat capacities of gadolinium trifluoride GdF3, lutetium trifluoride LuF3, and yttrium trifluoride YF3 from 5 to 350 deg K
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The heat capacities of three isostructural trifluorides GdF3, LuF3, and YF3 were determined from 5 to 350 deg K by adiabatic calorimetry.Below 15 deg K GdF3 contained an excess heat capacity contribution over the usual lattice heat capacity; LuF3 and YF3
- Flotow, Howard E.,O'Hare, P. A. G.
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- Polyol-mediated syntheses and characterizations of NaYF4, NH4Y3F10 and YF3 nanocrystals/sub-microcrystals
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In this paper, NaYF4 nanocrystals and NH4Y3F10 sub-microcrystals were prepared using a polyol method. After being annealed, NH4Y3F10 can convert into YF3, which is a very efficient host matrix for upconversion. The structures of obtained NaYF4, NH4Y3F10 and YF3 samples are pure cubic phase, a mixture of cubic and hexagonal phase and pure orthorhombic phase, respectively. The size of obtained NaYF4 nanocrystals is about 20 nm, and those of NH4Y3F10 and YF3 sub-microcrystals are both about 200 nm. When co-doped with Er3+ and Yb3+, NaYF4 and YF3 samples can emit bright light under 978 nm excitation. Upconversion mechanisms in Yb3+/Er3+ co-doped NaYF4 and YF3 samples were discussed.
- Qin, Ruifei,Song, Hongwei,Pan, Guohui,Hu, Lanying,Yu, Hongquan,Li, Suwen,Bai, Xue,Fan, Libo,Dai, Qilin,Ren, Xinguang,Zhao, Haifeng,Wang, Tie
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- Synthesis and characterization of mixed fluoride Y1-xSr2+1.5xF7 (-1.0 < x < 0.5)
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A series of mixed fluorides with the general formula Y1-xSr2+1.5xF7 (x = -1.0 0.5Sr2.75F7 shows a cubic symmetry (fluorite-type structure) with a = 5.776 angstrom. On decreasing the Sr2+ content or increasing the Y3+ content in Y1-xSr2+1.5xF7, a phase with tetragonal symmetry with a = 11.416 angstrom and c = 13.291 angstrom was observed in the composition YSr2F7, whereas in the composition Y2Sr0.5F7, a phase with hexagonal symmetry with a = 6.882 angstrom and c = 7.032 angstrom was observed. The existence of phases such as YSr2F7 and Y2Sr0.5F7 was confirmed. We observed a coexistence of rhombohedral and hexagonal phases beyond a particular nominal composition in this series of compounds.
- Patwe,Achary,Tyagi,Moorthy
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- YF3:Ln3+ (Ln = Ce, Tb, Pr) submicrospindles: Hydrothermal synthesis and luminescence properties
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YF3:Ln3+ (Ln = Ce, Tb, Pr) microspindles were successfully fabricated by a facile hydrothermal method. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), lifetimes, photoluminescence (PL) and low-voltage cathodoluminescence (CL) were used to characterize the resulting samples. The lengths and diameters of YF 3:0.02Ce3+ microspindles are around 760 nm and 230 nm, respectively. Adding dilute acid and trisodium citrate (Cit3-) are essential for obtaining YF3 microspindles. A potential formation mechanism for YF3 microspindles has been presented. PL spectroscopy investigations show that YF3:Ce3+ and YF 3:Tb3+ microcrystals exhibit the characteristic emission of Ce3+ 5d → 4f and Tb3+ 5D4 → 7FJ (J = 6-3) transitions, respectively. In addition, the energy transfer from Ce3+ to Tb3+ was investigated in detail for YF3:Ce3+, Tb3+ microspindles. Under the excitation of electron beams, YF3:Pr3+ show quantum cutting emission and YF3:Ce3+, Tb3+ phosphors exhibit more intense green emission than the commercial phosphor ZnO:Zn.
- Peng, Chong,Li, Chunxia,Li, Guogang,Li, Suwen,Lin, Jun
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- Problems in the thermal investigation of the BaF2-YF3 system
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The BaF2-YF3 system was partially investigated, with focus given to the BaY2F8 compound and its neighboring phases. In this report, various difficulties that hinder the thermal analysis investigation of this bin
- Nakamura,Baldochi,Mazzocchi,Parente,Valerio,Klimm
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- Ionic conductivity in solid solutions of PbF2 and YF3
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Ionic conductivity of a series of fluorite-type solid solutions Pb1-xYxF2+x (0.007 ≤ x ≤ 0.222) has been measured in the frequency range 100 Hz - 3 MHz and in the temperature range 25-250°C under vacuum. The conductivity decreases and the activation energy increases gradually upon increasing the yttrium content up to ~ 4.5 mol% of Y3+ whereas, beyond that and up to 22 mol% of Y3+, the ionic conductivity increases and the activation energy decreases. Thus two distinct regions in the general composition Pb1-xYxF2+x could be delineated, in one the polarizability factor predominates over the number of extra-interstitial F anions and vice-versa in the other region. These results indicate the competing effects between the disorder caused by interstitial F anions and the polarizability of the host and guest cations.
- Patwe,Balaya,Goyal,Tyagi
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- Studies on fluorination of Y2O3 by NH 4HF2
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Fluorination of Y2O3 by NH4HF2 to obtain pure YF3 is studied in this work by observing the mass changes at room temperature and by employing TGA and DTA at higher temperatures, and observing the subsequent phase changes by X-ray diffraction. Fluorination begins at room temperature with the formation of (NH4) 3Y2F9 and NH4F, and continues with the later further fluorinating any leftover Y2O3 to ammonium yttrium fluorides with the evolution of NH3. Similarly, on heating a mixture of Y2O3 and NH4HF 2, the reaction proceeds sequentially through the formation of (NH4)3Y2F9, NH4Y 2F7 and finally YF3. Any Y2O 3 still remaining reacts with YF3 to form yttrium oxyfluorides, which continue as impurity. Substantial evaporation of NH 4HF2 is possible even before it could participate in the reaction. This disturbs the stoichiometry of the charge causing oxygen to remain in final YF3. The compound reported in literature as YF 3·1.5NH3 appears to be NH4Y 2F7.
- Mukherjee, Abhishek,Awasthi, Alok,Mishra, Saurabh,Krishnamurthy, Nagaiyar
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p. 145 - 152
(2011/08/04)
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- Lanthanide doped Y6O5F8/YF3 microcrystals: Phase-tunable synthesis and bright white upconversion photoluminescence properties
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High-quality Y6O5F8/YF3 microcrystals have been synthesised by using a hydrothermal and subsequent calcination route. Upon changing the initial solution pH value, the as-prepared microcrystal can be well tuned from YF3 octahedron microcrystals to YF3 hollow spheres and finally to Y6O5F 8 microtubes. The as-obtained microcrystals have been characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectra. When the Y6O 5F8:Ln3+ microtubes are excited by a 980 nm continual wave laser diode, bright red, green, and blue room temperature upconversion PL emissions have been observed. A series of white light emissions have been obtained by precisely adjusting dopants concentration in Y 6O5F8 microtubes. The Royal Society of Chemistry 2010.
- Wang, Song,Deng, Ruiping,Guo, Hailing,Song, Shuyan,Cao, Feng,Li, Xiyan,Su, Shengqun,Zhang, Hongjie
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p. 9153 - 9158
(2011/01/11)
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- Characterization of CrOx-Y202 catalysts for fluorination of 2-chloro-1,1,1 -trifluoroethane
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The fluorination of 2-chIoro-1,1, 1-trifluoroethane (CF3CH 2C1) to synthesize 1,1,1,2-tetrafluoroethane (CF3CH 2F) has been carried out on various CrOx-Y 2O3 catalysts with different Cr loadings. The effect of Cr loading on the catalyst composition and structure has been investigated. X-ray diffraction and Raman results indicate that the CrOx species with high oxidation state (Cr(Vl)) are well dispersed on the catalyst surface when the Cr loading was lower than 19.5 %. With increase in Cr loading, crystalline Cr2O3 and polymeric chromate are formed, which inhibit pre-fluorination of the catalysts. The catalysts are stable under the reaction conditions and the catalytic activity is strongly dependant on the pre-fluorinated CrOx content. The highest activity is obtained on a pre-fluorinated catalyst with a Cr loading of 19.5, with a 19 % CF 3CH2CI conversion at 320 °C, corresponding to a formation rate of 2.03 mmol h-1g-1cat which is 3-fold higher than the best result obtained over a Cr/MgF2 catalyst (0.68 mmol h-1 g-1cat) under similar conditions. The Cr-Al2O3 catalyst has also been prepared and tested for the probe reaction in this study. The activity is lower as compared to that of the Cr-Y2O3 catalyst with the same Cr content. The higher activity of Cr-Y2O3 catalyst may be due to the higher degree of dispersion of the Cr(VI) species on the Y 2O3 support than on other supports. It is also found that the CrFx, CrOxFy or Cr(OH)xF y phases originating from higher oxidation state Cr(VI) species are the active sites for the fluorination reaction.
- He, Jun,Lu, Ji-Qing,Xie, Guan-Qun,Qian, Lin,Chen, Ke-Feng,Zhang, Xue-Liang,Luo, Meng-Fei
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p. 489 - 497
(2010/01/29)
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- Solubility of YF3, CeF3, PrF3, NdF 3, and DyF3 in solutions containing sulfuric and phosphoric acids
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The solubility of YF3, CeF3, PrF3, NdF3, and DyF3 in solutions containing 0-4.496% mol/L (0-35 wt %) of H2SO4 and 0-27.6 g/L of H 3PO4 (0-20 g/L of P2
- Lokshin,Tareeva
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p. 1830 - 1834
(2008/10/09)
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- Synthesis and characterization of ternary NH4Ln 2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) nanocages
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In this paper, a new class of NH4Ln2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) inorganic nanocages that has been discovered will be presented. A facile template-free synthetic route was developed for one step, high yield, and large scale synthesis of ternary NH4Ln 2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) nanocages. On the basis of our studies, these nanocages are thermodynamically stable forms of this group of NH4Ln2F7 compounds. The tendency of NH 4Ln2F7 (Ln = Y, Ho, Er, Tm, Yb, Lu) to form these new-type nanostructures is believed to have a close relationship with their inherent layered structures, similar to that of inorganic fullerene-like nanoparticles. This new type of nanocage can be easily doped with other lanthanide ions, which may endow these nanocages with novel properties. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Liang, Xin,Wang, Xun,Wang, Leyu,Yan, Ruoxue,Peng, Qing,Li, Yadong
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p. 2186 - 2191
(2007/10/03)
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- Hydrothermal synthesis of rare-earth fluoride nanocrystals
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In this paper, a hydrothermal synthetic route has been developed to prepare a class of rare-earth fluoride nanocrystals, which have shown gradual changes in growth modes with decreasing ionic radii and may serve as a model system for studying the underlying principle in the controlled growth of rare-earth nanocrystals. Furthermore, we demonstrate the functionalization of these nanocrystals by means of doping, which have shown visible-to-the-naked-eye green up-conversion emissions and may find application in biological labeling fields.
- Wang, Xun,Zhuang, Jing,Peng, Qing,Li, Yadong
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p. 6661 - 6665
(2008/10/09)
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- Fullerene-like rare-earth nanoparticles
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A low-temperature hydrothermal synthesis has been employed to prepare the title materials in the form of their fluorides and hydroxides. Electron microscopy reveals their hollow and closed-cage structures (see HRTEM image). Such nanostructures can be expected to bring forth new opportunities in important research and application fields, such as biological labeling, luminescence, and catalysis.
- Wang, Xun,Li, Yadong
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p. 3497 - 3500
(2007/10/03)
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- Hydrofluoride synthesis of fluorides of some rare-earth elements
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Thermal gravimetric, X-ray phase, IR spectroscopic, and chemical analyses were applied to study the reaction of yttrium and neodymium oxides with NH 4HF2.
- Kalinnikov,Makarov,Tikhomirova,Elizarova,Kuznetsov
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p. 1760 - 1764
(2007/10/03)
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- Laser development of rare-earth doped crystals
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Rare earth doped laser crystals present good optical properties providing most of the solid state lasers available today. In particular, some fluoride crystals are capable of forming solid solution with several rare earth fluorides, allowing one to take full advantage of the energy transfer mechanisms that might occur among them. LiREF4 (RE = rare earth) crystals, for example, are so flexible that in some cases the doping concentration can go up to 100%. The Nd:LiLuF4 (Nd:LuLF) system has a 1047-nm emission bandwidth 25% larger than Nd:YLF, which makes it very promising for laser mode-locked operation. Nevertheless, lutetium compounds are very difficult to obtain, therefore Nd-doped mixed crystals grown from LiF-Y1-xLuxF3 (0A new laser medium was obtained for the Nd:LiLu0.5Y0.5F4 crystal, which presents a Nd emission bandwidth close to the Nd:LuLF (1.82 nm). The mode-locked operation in a diode pumped laser system using the KLM technique was performed and pulses of 4.5 ps were readily obtained. It is also shown that the LiGdF4 (GLF) is a promising host for diode pumped high power Nd lasers which require crystals with higher dopant concentrations. Another example is the Ho:LiYF4 (Ho:YLF) laser operating at 2065 nm obtained as a result of concentration optimization of the sensitizers Er and Tm. The optimization was based on a model comprising the various energy transfer mechanisms that take place in these long lived metastable states, heavily dependent on the dopants concentration. As a quasi-four-level system, the Ho concentration must be kept very small (≤0.005 mol%). The laser operation was optimized by the dynamical coupling of pump and laser modes, and by the dopants optical cycle. These optimizations resulted in a CW Ho laser with 2 W output, in a diode pumped system operation.
- Vieira Jr.,Ranieri,Tarelho,Wetter,Baldochi,Gomes,De Matos,De Rossi,Nogueira,Courrol,Barbosa,Maldonado,Morato
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p. 231 - 239
(2008/10/08)
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- Hydrothermal syntheses and crystal structure of NH4Ln3F10 (Ln = Dy, Ho, Y, Er, Tm)
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Ammonium rare earth fluorides NH4Ln3F10 (Ln = Dy, Ho, Y, Er, Tm) were synthesized by a hydrothermal method. Two polymorphs, of the hexagonal β-KYb3F10 and the cubic γ-KYb3F10 structure types, were formed under hydrothermal conditions for most of the rare earth fluorides except NH4Dy3F10, for which only the cubic γ-phase was obtained. The crystal structures of MLn3F10 (M = alkaline metal, NH4+ and Ln = rare earth) show a strong correlation to the ratio of ionic radii (RM/RLn), which has been expressed in a structure phase diagram of the ionic radii of univalent and rare earth cations.
- Kang,Wang,You,Lin
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p. 358 - 362
(2008/10/08)
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- Heterobimetallic d-f Metal Complexes as Potential Single-Source Precursors for MOCVD: Structure and Thermodynamic Study of the Sublimation of [Ni(salen)Ln(hfa)3], Ln = Y, Gd
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Heterobimetallic [Ni(salen)Ln(hfa)3] species [H2salen and Hhfa being N,N′-ethylenebis(salicylideneimine) and hexafluoroacetylacetone respectively], where Ni(salen) acts as a neutral chelating ligand towards LnIII, form a s
- Gleizes, Alain,Julve, Miguel,Kuzmina, Natalia,Alikhanyan, Andrei,Lloret, Francesc,Malkerova, Irina,Sanz, Jose Luis,Senocq, Francois
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p. 1169 - 1174
(2007/10/03)
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- Study of phase transition in REOF system by dilatometry (RE = La, Nd, Sm, Gd, Eu and Y)
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Bulk thermal expansion behaviour of a number of rare earth oxyfluorides (REOF) has been studied using dilatometry in the temperature range 289-923 K in air. The studies revealed an anomalous expansion for each compound associated with the phase transition. The phase transition temperatures and the coefficients of average linear thermal expansion of the compounds determined by this method are reported.
- Mathews,Tyagi,Moorthy
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p. 165 - 167
(2008/10/09)
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- Thermodynamics of the rhombohedral-cubic phase transition of ROF with R=Y, La, Pr, Nd, Sm-Er
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The temperatures and enthalpies of the rhombohedral-cubic phase transition of stoichiometric ROF with R=Y, La, Pr, Nd, Sm-Er, have been determined by differential scanning calorimetry. The temperatures of transition are found in the range 742-880 K in sat
- Petzel,Marx,Hormann
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- Synthesis and thermal study of tris(ammonium) hexafluoro metallates(III) of some rare earths
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Fluorination of oxides of rare earths using ammonium hydrogen fluoride at room temperature gave new compounds 3MF6*nH2O, where M = Y, La, Nd, and Pr.In the case of cerium, 4CeF8 is formed.The course of thermal decomposition of all these compounds is studied by thermogravimetry/differential thermal analysis (TG/DTA) and X-ray powder diffraction(XRD).Key words: hexafluoro metallates, rare earths, ammonium hydrogen fluoride, thermal decomposition, X-ray diffraction.
- Patwe, S. J.,Wani, B. N.,Rao, U. R. K.,Venkateswarlu, K. S.
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p. 1815 - 1818
(2007/10/02)
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- PREPARATION OF Rb2NaYF6:Ce3 + AND Cs2NaYF6:Ce3 + - A PROSPECT FOR TUNABLE LASERS IN THE BLUE-GREEN WAVELENGTH.
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A systematic study of the systems RbF-NaF-YF//3 and NaF-CsF-YF//3 has been made in order to synthesize Ce**3** plus -doped Rb//2NaYF//6 and Cs//2NaYF//6. Based on preliminary results of the absorption fluorescence efficiency, lifetime, and excited-state absorption, we conclude that a series of compounds (in the form of single crystals) of the general form A//2BYF//6:Ce**3** plus is a worthy prospect for a broad-band, wavelength tunable laser from 400 to 480 mu m which makes it attractive for optical communication.
- Mroczkowski,Dorain
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p. 259 - 265
(2008/10/08)
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- PREPARATION, THERMAL CHARACTERIZATION AND X-RAY POWDER DIFFRACTION OF Ba2REF7 SUPERSTRUCTURE PHASES (RE EQUVLNT Dy-Lu, Y).
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Thermal analyses on samples of the composition (Ba, RE)F//2//,//3//3 revealed seven new compounds Ba//2REF//7 (RE EQUVLNT Dy-Lu, Y). They are stable only above about 940 degree C but can be quenched after annealing for several days at 950-1000 degree C. These phases, which are metastable at room temperature, were characterized by X-ray powder diffraction. A tetragonal distortion of the fluorite parent structure was detected, analogous to that in the Ln//3F//7, Ca//2REF//7, and Sr//2REF//7 phases. In contrast, however, the superstructure is not fully pronounced and only tripling along the c axis is observed.
- Kieser,Greis
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- The sodium fluoride-lanthanide trifluoride systems
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Phase diagrams are reported for the NaF-LnF3 binary systems. Hexagonal phases of the formula NaF·LnF3 are formed in all NaF-LnF3 systems. Above 700° the hexagonal phases NaF·PrF3 to NaF·LuF3 become converted to disordered fluorite-like cubic phases of variable composition. The composition limits of the cubic phase region are extended in proportion to the difference in ion size between Na+ and Ln3+ and vary in breadth ranging from 9 mole % (NaF-PrF3) to 25 mole % (NaF-LuF3). In each case, the LnF3-rich phase boundary was found empirically to be 5NaF·OLnF3 as the interstitial positions for allions become filled. Values of the fluorite unit-cell constants were calculated from ionic radii and found to be in good agreement with measured values. Unit-cube dimensions, a0, range from a maximum value of 5.720 A for the LnF3-rich phase in the system NaF-PrF3 to 5.425 A for the NaF-rich phase in the system NaF-LuF3. Lattice constants for the hexagonal phases NaF·LaF3 to NaF·LuF3 vary for a0 from 6.157 to 5.907 A and for C0 from 3.822 to 3.523 A. At high temperatures the 5NaF·9LnF3 phase displays disordering characteristic of the fluorite-like solid solutions; at lower temperatures cationic ordering takes place in the 5NaF·OLnF3 phases where Ln = Dy to Lu, transforming the cubic phase to an orthorhombic phase. Hexagonal NaF·LnF3 and orthorhombic 5NaF·OLnF3 compounds are partially miscible in the solid state. In the series Dy to Lu, the hexagonal phase is increasingly soluble in 5NaF·OLnF3, stabilizing the 5:9 phase to the extent that the lutetium compound is stable at temperatures below 300°, the lower temperature limit of this study. Optical properties and refractive indices of the intermediate crystalline phases in the NaF-LnF3 systems were determined as part of this investigation. Minimum liquidus temperatures in the NaF-LnF3 systems are associated with an NaF-NaF·LnF3 eutectic which varies in composition only from 25 to 29 mole % LnF3 and in temperature from 733 to 595°.
- Thoma,Insley,Hebert
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p. 1222 - 1229
(2008/10/08)
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