A rare multi-coordinate tellurite, NH4ATe4O9·2H2O (ARb or Cs): The occurrence of TeO3, TeO4, and TeO5 Polyhedra in the same material

Two new tellurites, NH₄RbTe₄O₉·2H₂O and NH₄CsTe₄O₉·2H₂O have been synthesized and characterized. The compounds were synthesized hydrothermally, in near quantitative yields, using the alkali metal halide, TeO₂, and NH₄OH as reagents. The iso-structural materials exhibit layered, two-dimensional structural topologies consisting of TeO_x (x=3, 4, or 5) polyhedra separated by NH₄⁺, H₂O, Rb⁺ or Cs⁺ cations. Unique to these materials is the presence of TeO₃, TeO₄, and TeO₅ polyhedra. Thermogravimetric and infrared spectroscopic data are also presented. Crystal data: NH₄RbTe₄O₉·2H₂O: Monoclinic I2/a (no. 15), a=18.917(3) Å, b=6.7002(11) Å, c=21.106(5) Å, β=101.813(2)°, V=2618.5(9) Å³, Z=8; NH₄CsTe₄O₉·2H₂O: Monoclinic I2/a (no. 15), a=18.9880(12) Å, b=6.7633(4) Å, c=21.476(2) Å, β=102.3460(10)°, V=2694.2(3) Å³, Z=8.     

Synthesis and spectrum stability of high quality CdTe quantum dots capped with stearate groups in N-oleoylmorpholine solvent

The stearate-capped CdTe quantum dots (QDs) have been first prepared via direct reaction of cadmium stearate with Te powder in N-oleoylmorpholine solvent, which was a kind of clean, air-stable and conveniently synthesized acylamide, and can readily dissolve precursors cadmium stearate and Te powder at a relative low temperature. The as-prepared CdTe QDs exhibited size-dependent optical properties, steep absorbance edge and narrow photoluminescence full width at half maximum. The high-resolution transmission electron microscopy images and X-ray diffraction revealed that the highly monodisperse CdTe QDs were of regular spherical morphology with zinc blende crystal structure displaying mean sizes of about 4 nm. The energy dispersed spectrometry measurement indicated the presence of Cd and Te, with the Cd:Te ratio being close to 1:1. Fourier transform infrared transmission spectra confirmed the existence of stearate on the CdTe QDs surfaces. The experimental results also demonstrated that the stearate-capped CdTe QDs had an unexpected good stability.     

Production of high purity TeO2 single crystals for the study of neutrinoless double beta decay

High purity TeO₂ crystals are produced to be used for the search for the neutrinoless double beta decay of ¹³⁰Te. Dedicated production lines for raw material synthesis, crystal growth, and surface processing were built compliant with radio-purity constraints specific to rare event physics experiments. High sensitivity measurements of radio-isotope concentrations in raw materials, reactants, consumables, ancillaries, and intermediary products used for TeO₂ crystals production are reported. Indications are given on the crystals perfection and how it is achieved and maintained in a large scale production process. Production and certification protocols are presented and resulting ready-to-use TeO₂ crystals are described.     

WDM Systems in the C-Band Using Er 3+ -Doped Tellurite Optical Waveguide Amplifiers

A 16-channel, 2.5 Gb/s, wavelength-division multiplexing system is analyzed with its channels allocated in the 1.52-1.56 w m wavelength region in order to increase the usable amplifier bandwidth to , 45 nm. To avoid amplified spontaneous emission (ASE) noise and the nonuniform signal gain in the wavelength region, an amplifier module consisting of an Er 3+ -doped tellurite waveguide amplifier, an ASE filter, and two concatenated long-period grating filters are proposed. A tellurite-based amplifier was chosen as the amplifying element because of its broad emission bandwidth (~80 nm), its high emission cross section (6.44 2 10 -25 m 2 ), and its high rare-earth ion solubility. The amplifier model is based on propagation and populationrate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and a Runge-Kutta algorithm. The analysis predicts that using the proposed amplifier module, the channels may be transmitted to a maximum distance of 1800 km, finding applications in large optical networks where either many wavelengths are required or channel spacing must be large.     

Three new tellurite halides with unusual Te coordinations and iron honeycomb lattice variants

The crystal structure of three new iron and copper-iron tellurite halides are presented; (I) Cu₃Fe₈Te₁₂O₃₂Cl₁₀ that crystallizes in the orthorhombic space group Pmmn, (II) Fe₈Te₁₂O₃₂Cl₃Br₃ that crystallizes in the monoclinic space group P2₁/c, and (III) Fe₅(TeO₃)₆Cl₂ that crystallizes in the triclinic space group P-1. The crystal structures were solved from single crystal X-ray diffraction data. All three compounds have layered crystal structures where the Fe atoms form variants of the honeycomb lattice. Highly unusual Te⁴⁺ coordination polyhedra are exemplified: [TeO₃₊₁E], [TeO₃XE], [TeO₃₊₁XE], and [TeO₃X₂E] (X=halide ion, E=the lone-pair valence electrons). The crystal structures contain large non-bonding volumes occupied by the stereochemically active lone-pair electrons on Te⁴⁺.     

Synthesis,Band and Crystal Structures,and Optical Properties of the Ternary Compound Mg2Te3O8

The new spiroffite Mg₂Te₃O₈ ( 1 ) was prepared by hydrothemal methods and structurally characterized by single‐crystal X‐ray diffraction analysis. Compound 1 crystallizes in the space group C2/c of the monoclinic system with two formula units in a cell: a = 12.6030(7), b = 5.2254(3), c = 11.6331(7) Å, β = 98.6960(10)°, V = 757.30(8) ų. The structure features a 3D open‐framework with spiroffite topology that has large tunnels approximately 3.2 × 5.5 Å. The optical properties and thermal stability of 1 were characterized by UV and IR spectroscopy as well as TG. Calculations of the electronic band structure along with the density of states (DOS) indicate that the present compound is a semiconductor with an indirect band gap, and that the optical absorption is mainly originated from the charge transitions from O‐2p state to Te‐5p and Te‐5s states.     

Optical properties of Ge-As-Te thin films

Different compositions of Ge_xAs₁₀Te_90−x (x=5, 10, 15, 20, and 25 at%) chalcogenide glasses were prepared by the usual melt quench technique. Amorphous Ge_xAs₁₀Te_90−x thin films were deposited onto cleaned glass substrates using the thermal evaporation method. Transmission spectra, T(λ), of the films at normal incidence were measured in the wavelength range 400-2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. It was found that, the addition of Ge content at the expense of Te atoms shifts the optical band gap to the short wavelength side (blue shift of the optical band gap) while the refractive index are found to decreases. The obtained results of the refractive index were discussed in terms of the electronic polarizability and the single-oscillator Wemple and DiDomenico model (WDD). The optical absorption is due to the allowed non-direct optical transitions. The observed increase in the optical band gap with the increase in Ge content was discussed in terms of the width of the tail states in the gap and the covalent bond approach.     

A novel approach for the fabrication of planar waveguides from heavy metal oxide glasses

An extrusion process is used to fabricate preforms for the development of planar waveguides in glass ribbon format through a stretching process. The feasibility of the overall process is demonstrated using three tellurite glass compositions. The manufactured preforms present multilayered structures with the higher refractive glass layer thickness of the order of 40 μm. The longitudinal and transversal variations of the layer thicknesses are discussed with respect to waveguiding application tolerances. Advantages, limitations and improvement of the technique are also discussed. 3 mm wide multilayered planar waveguides in ribbon geometry are produced by stretching the preforms by a 1:5 ratio over a length of 400 mm. The waveguides were examined by optical and electron microscopy and no signs of crystallization or contamination are observed. Optical waveguiding is successfully assessed in 7.4 μm thick and 9 mm long film waveguides.     

WDM Systems in the C-Band Using Er 3+ -Doped Tellurite Optical Waveguide Amplifiers

A 16-channel, 2.5 Gb/s, wavelength-division multiplexing system is analyzed with its channels allocated in the 1.52-1.56 μm wavelength region in order to increase the usable amplifier bandwidth to ≈45 nm. To avoid amplified spontaneous emission (ASE) noise and the nonuniform signal gain in the wavelength region, an amplifier module consisting of an Er 3+ -doped tellurite waveguide amplifier, an ASE filter, and two concatenated long-period grating filters are proposed. A tellurite-based amplifier was chosen as the amplifying element because of its broad emission bandwidth (~80 nm), its high emission cross section (6.44 ×10 -25 m 2 ), and its high rare-earth ion solubility. The amplifier model is based on propagation and populationrate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and a Runge-Kutta algorithm. The analysis predicts that using the proposed amplifier module, the channels may be transmitted to a maximum distance of 1800 km, finding applications in large optical networks where either many wavelengths are required or channel spacing must be large.