Si2 O7 Research Articles

Structural, morphological, and optical characteristics of Gd2 Si2 O7 :Dy3+ nanophosphors for WLEDs.

Yellowish-white light-emitting Gd2-x Si2 O7 :xDy3+ (x = 1-5 mol%) nanophosphors were prepared using a solution combustion synthesis method. Fluorescence spectrophotometry and X-ray diffraction measurements were performed to scrutinize the optical performances and phase recognition of the designated nanophosphors. The outcomes specified that the prepared phosphors were crystallized into a triclinic phase with a P-1 space group. As the concentration of Dy3+ ions was increased, the unit-cell volume decrease proportionally due to the replacement of large-sized Gd3+ by small-sized Dy3+ ions. Under ultraviolet excitation at 349 nm, emission spectra consisted of two pronounced emission lines at ~482 nm (blue line), ~578 nm (yellow line), and a relatively weaker emission at ~670 nm (red line) due to 4 F9/2 →6 H15/2 , 4 F9/2 →6 H13/2 , and 4 F9/2 →6 H11/2 intraconfigurational transitions of Dy3+ ions, respectively. The evidence about the site symmetry around Dy3+ ions was examined by considering the ratio of yellow-to-blue emission intensity. The observed critical distance (Rc ) value was ~20.56 Å (≫5 Å), which signified that energy transfer primarily occurred due to multipolar interaction. The obtained coordinates were close to the white region of the Commission Internationale de l'Éclairage chromaticity diagram, which marked a significant milestone in the development of white light-emitting diodes.

Molten Salts-Driven Discovery of a Polar Mixed-Anion 3D framework at the nanoscale: Zn4Si2O7Cl2, Charge Transport and Photoelectrocatalytic Water Splitting.

Mixed-anion compounds widen the chemical space of attainable materials compared to single anionic compounds, but the exploration of their structural diversity is limited by common synthetic paths. Especially, oxychlorides rely mainly on layered structures, which suffer from low stability during photo(electro)catalytic processes. Herein we report a strategy to design a new polar 3D tetrahedral framework with composition Zn4Si2O7Cl2. We use a molten salt medium to enable low temperature crystallization of nanowires of this new compound, by relying on tetrahedral building units present in the melt to build the connectivity of the oxychloride. These units are combined with silicon-based connectors from a non-oxidic Zintl phase to enable precise tuning of the oxygen content. This structure brings high chemical and thermal stability, as well as strongly anisotropic hole mobility along the polar axis. These features, associated with the ability to adjust the transport properties by doping, enable to tune water splitting properties for photoelectrocatalytic H2 evolution and water oxidation. This work then paves the way to a new family of mixed-anion solids.

Synthesis, Structure and Properties of an Extra‐Large‐Pore Aluminosilicate Zeolite NUD‐6

Pure silica zeolites possessing uniform micropores, large surface area and high thermal and chemical stability have been widely studied and used in the fields of fine chemicals and oil industry. The incorporation of aluminium into the framework of silica zeolites changes their properties, making them more industrially useful as adsorbents and catalysts. Herein, we report the synthesis and characterization of an extra-large-pore aluminosilicate zeolite NUD-6 with a 16-membered-ring pore channel. Aluminium was directly incorporated into the zeolite NUD-6 framework, as confirmed by 27 Al MAS NMR studies and ammonia temperature-programmed desorption probes. Al-NUD-6 was not stable when heated at 550 °C to remove the organic templates. However, the organic templates in Al-NUD-6 could be removed by oxidation in nitric acid at room temperature. The obtained Al-NUD-6H retained the crystalline structure and possessed both micropores and mesopores despite the occurrence of severe structural distortions due to the presence of the corner-sharing Q3 Si2 O7 units. The incorporation of aluminium resulted in both medium and strong acid sites in Al-NUD-6H, and could facilitate its use in adsorption and catalysis.

Beta-ray imaging system with γ-ray coincidence for multiple-tracer imaging.

Beta-ray imaging systems are widely used for various biological objects to obtain a two-dimensional (2D) distribution of β-ray emitting radioisotopes. However, a conventional β-ray imaging system is unsuitable for multiple-tracer imaging, because the continuous energy distribution of β-rays complicates distinguishing among different tracers by energy information. Therefore, we developed a new type of β-ray imaging system, which is useful for multiple tracers by detecting coincidence γ-rays with β-rays, and evaluated its imaging performance. Our system is composed of position-sensitive β-ray and γ-ray detectors. The former is a 35×35×1-mm3 Ce-Doped((La, Gd)2 Si2 O7 ) (La-GPS) scintillation detector, which has a 300-µm pitch of pixels. The latter is a 43×43×16-mm3 bismuth germanium oxide (BGO) scintillation detector. Both detectors are mounted on a flexible frame and placed in a user-selectable position. We experimentally evaluated the performance of the β-ray detector and the γ-ray efficiencies of the γ-ray detector with different energies, positions, and distances. We also conducted point sources and phantom measurements with dual isotopes to evaluate the system performance of multiple-tracer imaging. For the β-ray detector, the β-ray detection efficiencies for 45 Ca (245-keV maximum energy) and 90 Sr/90 Y (545 and 2280-keV maximum energy) were 14.3% and 21.9%, respectively. The total γ-ray detection efficiency of the γ-ray detector for all γ-rays from 22 Na (511-keV annihilation γ-rays and a 1275-keV γ-ray) in the center position with a detector distance of 20mm was 17.5%. From a point-source measurement using 22 Na and 90 Sr/90 Y, we successfully extracted the position of a positron-γ emitter 22 Na. Furthermore, for a phantom experiment using 45 Ca and 18 F or 18 F and 22 Na, we successfully extracted the distribution of the second tracer using the annihilation γ-ray or de-excitation γ-ray coincidence. In all the imaging experiments, the event counts of the extracted images were consistent with the counts estimated by the measured γ-ray efficiencies. We successfully demonstrated the feasibility of our β-ray autoradiography system for imaging multiple isotopes. Since our system can identify not only a β-γ emitter but also a positron emitter using the coincidence detection of annihilation γ-rays, it is useful for PET tracers and various new applications that are otherwise impractical.

Temperature-induced iron oxidation in bafertisite Ba2Fe 4 2 + ${}_{4}^{2+}$ Ti2(Si2O7)2O2(OH)2F2: X-ray diffraction and Mössbauer spectroscopy study

The high-temperature behavior of bafertisite was studied by combination of techniques in order to characterize the temperature-induced iron oxidation associated with deprotonation of an octahedral layer. The chemical formula of bafertisite from Darai-Pioz alkaline complex (Tajikistan) determined by electron-microprobe analyzes and Mossbauer spectroscopy is Ba 2.11(Fe ${}_{2.70}^{2+}$ Fe ${}_{0.17}^{3+}$ Mn 1.09Zr 0.04Na 0.03) (Ti 1.96Nb 0.07)(Si 2 O 7)2 O 2(OH 1.29 O 0.65 F 0.06)F 2. In situ high-temperature powder X-ray diffraction revealed abrupt shift of reflections to the high-angle region and reduction of their intensity at T > 525 ∘C. The Mossbauer spectroscopy studies indicated that the crystal structure of bafertisite contains Fe in octahedral sites as predominantly ferric ions with Fe 3+/ ΣFe = 0.06, whereas bafertisite annealed at T = 600 ∘C has Fe in the same position with Fe 3+/ ΣFe up to 0.39. The differential scanning calorimetry and thermogravimetric analyzes reveal the occurrence of a broad exothermic effect at T ∼ 537 ∘C associated with the mass loss corresponding to deprotonation. Since in the studied sample of bafertisite, Fe 2+ apfu strongly prevails over OH apfu, the stoichiometric (charged-balanced) high-temperature oxidized modification cannot be obtained. In the paper, the high-temperature behavior of bafertisite is discussed and compared to that of astrophyllite.

Thermodynamic assessment of Al2O3–SiO2–Ce2O3system

The Al2 O3 –SiO2 , Ce2 O3 –Al2 O3 and Ce2 O3 –SiO2 binary systems were assessed by Redlich–Kister expression based on the sub-regular solution model. Then, the Al2 O3 –Ce2 Si2 O7 system was calculated on the basis of existing experimental data. All the interaction parameters related to the Al2 O3 –SiO2 –Ce2 O3 system were given. The calculated phase diagrams were proved to be accurate when compared with the experimental points or the similar phase diagrams. Finally, a series of phase diagrams were present about the Al2 O3 –SiO2 –Ce2 O3 system.

ChemInform Abstract: Eu2+ Luminescence in Ca3Si2O7 and Spectral Widening and Tuning of Eu2+ Emission Color (Orangish‐Red to Green) by Crystal Chemical Substitution.

AbstractA series of yellowish‐orange emitting phosphors Ca3‐xEuxSi2O7 (x = 0.0025—0.03) and Ca2.985‐yMgyEu0.015Si2 O7 (y = 0—1) are prepared by calcination of stoichiometric amounts of CaCO3, Eu2O3, Mg(NO3)2 and SiO2 in air (1250 °C, 6 h) followed by heating of the as‐prepared material in a 5%H2/N2 atmosphere (1275 °C, 6 h).

Evidence of yttrium silicate inclusions in YSZ‐porcelain veneers

This report introduces the discovery of crystalline defects that can form in the porcelain veneering layer when in contact with yttria-stabilized zirconia (YSZ). The focus was on dental prostheses and understanding the defects that form in the YSZ/porcelain system; however the data reported herein may have broader implications toward the use and stability of YSZ-based ceramics in general. Specimens were cut from fully sintered YSZ plates and veneering porcelain was applied (<1 mm thick) to one surface and fired under manufacturer's recommended protocol. Scanning electron microscopy (SEM) with integrated electron dispersive X-ray (EDAX) was used for microstructural and elemental analysis. EDAX, for chemical analysis and transmission electron diffraction (TED) for structural analysis were both performed in the transmission electron microscope (TEM). Additionally, in order to spatially resolve Y-rich precipitates, micro-CT scans were conducted at varying depths within the porcelain veneer. Local EDAX (SEM) was performed in the regions of visible inclusions and showed significant increases in yttrium concentration. TEM specimens also showed apparent inclusions in the porcelain and selected area electron diffraction was performed on these regions and found the inclusions to be crystalline and identified as either yttrium-silicate (Y2 SiO5 ) or yttrium-disilicate (Y2 Si2 O7 ). Micro-CT data showed that yttrium-silicate precipitates were distributed throughout the thickness of the porcelain veneer. Future studies are needed to determine whether many of the premature failures associated with this materials system may be the result of crystalline flaws that form as a result of high temperature yttrium diffusion near the surfaces of YSZ.

Cerchiaraite-(Fe) and cerchiaraite-(Al), two new barium cyclosilicate chlorides from Italy and California, USA

AbstractThe ideal formula for members of the cerchiaraite group is Ba4M4(Si4O12)O2(OH)4Cl2[Si2O3(OH)4], where M represents Mn3+, Fe3+ or Al in the octahedral site. A suffix-based naming scheme is used in which the original cerchiaraite is renamed cerchiaraite-(Mn) and two new minerals are named cerchiaraite-(Fe) and cerchiaraite-(Al). The type localities for cerchiaraite-(Fe) are the Cerchiara mine, Liguria, Italy and the Esquire No. 7 and No. 8 claims, Big Creek, Fresno County, California, USA. The type localities for cerchiaraite-(Al) are the Esquire No. 1 claim, Rush Creek, Fresno County, California, USA and the Esquire No. 7 and No. 8 claims noted above. At the Cerchiara mine, cerchiaraite-(Fe) occurs in small fractures and veinlets in a Jurassic ophiolitic sequence. It is of secondary hydrothermal origin and occurs as tan to brown thin prisms and matted fibres. Cerchiaraite(Fe) and cerchiaraite-(Al) from the Esquire No. 1, No. 7 and No. 8 claims occur in parallel-bedded quartz-sanbornite vein assemblages which formed as a result of fluid interaction along the margin of the vein. At the Esquire No. 1, No. 7 and No. 8 claims, both cerchiaraite-(Fe) and cerchiaraite-(Al) occur as subparallel aggregates of blue to bluish green irregular prisms. Both minerals are transparent with a vitreous lustre, Mohs hardness ~4½ , brittle tenacity, irregular fracture and no cleavage. The calculated density of cerchiaraite-(Fe) is 3.710 g cm-3; the measured density of cerchiaraite-(Al) is 3.69(3) g cm-3and the calculated density is 3.643 g cm-3. Cerchiaraite-(Fe) is uniaxial (+), with ω = 1.741(2) and ε = 1.768(2); it is weakly pleochroic and O is colourless and E is yellow. Cerchiaraite-(Al) is uniaxial (-), with ω = 1.695(2) and e = 1.677(2); it is strongly pleochroic and O is colourless and E is blue. Electron-microprobe analyses yielded empirical formulae ranging from (Ba3.82Na0.02Ca0.04)Σ3.88(Fe3+3.42Ti4+0.27Al3+0.25Mn3+0.04Mg0.02)Σ4.00Si5.62O15.47(OH)9.31Cl2.22 (Cerchiara mine) to Ba4.00(Al3+2.40Fe3+1.12Mg0.15Fe2+0.12Mn2+0.06)Σ3.85Si5.78O15.34(OH)8.75Cl2.91 (Esquire No. 1 claim). Cerchiaraite is tetragonal with Z = 2 and crystallizes in space group I4/mmm. The cell parameters for cerchiaraite-(Fe) are a = 14.3554(12), c = 6.0065(5) Å and V = 1237.80(5) Å3; those for cerchiaraite(Al) are a = 14.317(4), c = 6.0037(18) Å and V = 1230.6(6) Å3. In the cerchiaraite-(Fe) structure, SiO4 tetrahedra share corners forming a four-membered Si4O12 ring. The ring is corner-linked to an edgesharing chain of Fe3+ O6 octahedra running parallel to c. A Cl site alternates along c with the Si4 O12 ring. A large channel in the framework contains Ba atoms around its periphery and statistically distributed Si2 O7 silicate dimers and Cl atoms. The strong blue pleochroic colour is attributed to Fe2+ - Fe3+intervalence charge transfer along the octahedral chain.

Blue-to-Orange Tunable Luminescence from Europium Doped Yttrium–Silicon–Oxide–Nitride Phosphors

Europium-doped yttrium–silicon–oxide–nitride phosphors are synthesized by carbothermal reduction and nitri-dation method. The crystal structure of the phosphors changed gradually from oxide Y2 Si2 O7 to nitride YSi3 N5 state with increasing dosage of Si3N4 and carbon powder. The Y2 Si2 O7: Eu phosphor shows a blue emission at 465nm with 300nm excitation and a characteristic red emission of Eu3+ at 612nm with 230nm excitation. The YSi3 N5: Eu phosphor shows a broad emission band centred at 595nm with some sharp peaks of Eu3+ with 325nm excitation. The absorption of the studied phosphors increases from 450 to 700 nm with an increment in nitrogen content. Blue-to-orange tunable luminescence is observed with 390 nm excitation.

Crystal structures of lamprophyllite-2M and lamprophyllite-2O from the Lovozero alkaline massif, Kola peninsula, Russia

The crystals of lamprophyllite-2 M and lamprophyllite-2 O were found coexisting in an ussingite-microcline-sodalite veins in the Alluaiv Mt., Lovozero alkaline massif, in association with ussingite, aegirine, microcline, sodalite, albite, mangan- neptunite, vuonnemite, sphalerite, lomonosovite and betalomonosovite. The chemical composition of the polytypes corresponds to the formula (Sr 1.18Na0.66Ca0.12)S1.96Na (Na1.30Mn0.36Fe0.22Mg0.12)S2.00Ti3O2(Si2O7)2(OH)2. The structures of lamprophyllite-2 M (C2/m, a = 19.215(5), b = 7.061(2), c = 5.3719(15) A , b = 96.797(4) o, V = 723.7(4) A3) and lamprophyllite-2 O (Pnmn, a = 19.128(4), b = 7.0799(14), c = 5.3824(11) A , V = 728.9(3) A3) have been refined to R = 0.040 for 688 reflections (| Fo| ‡ 4sF) and to R = 0.084 for 571 reflections (| Fo| ‡ 4sF), respectively. The structures of both polytypes are based on the HOH layer consisting of a central O sheet of edge-sharing Na(1)O 6, Na(2)O6 and Ti(2)O6 octahedra sandwiched between two heterophyllosilicate H sheets. The H sheet is built by corner-sharing of Ti(1)O 5 square pyramids and Si 2O7 groups and consists of two types of rings of polyhedra: (i) six-membered rings (6 R) formed by two Si 2O7 groups and two TiO 5 square pyramids and (ii) four-membered rings (4R) formed by two silicate tetrahedra and two TiO 5 square pyramids. The Sr atom is located in the interlayer and is coordinated by six anions from 6 R of the upper H sheet and four anions from 4 R of the lower H sheet. The difference between monoclinic and orthorhombic lamprophyllites can be described in terms of different orientations of HOH layers. Whereas in lamprophyllite-2 M, all HOH layers are in the same orientation, in lamprophyllite-2 O, two adjacent layers are in different orientations.