Effect of lead oxide on optical properties of Dy3+ ions in PbO–H3BO3–TiO2–AlF3 glasses

The effect of lead oxide (PbO) on optical properties of Dy³⁺-doped PbO–H₃BO₃–TiO₂–AlF₃ (LBTAFDy) glasses is investigated. The LBTAFDy glasses were prepared with different PbO contents ranging from 30 to 60 mol%. The Judd–Ofelt intensity parameters (Ω_{λ = 2, 4, 6}) are obtained by the least square fit analysis. It is found that the Ω₂ parameter and yellow-to-blue intensity ratio (Y/B) of the Dy³⁺ emission depend on the PbO content in LBTAFDy glass. The structural asymmetry around the Dy³⁺ ion and the DyO covalency are responsible for the changes in Ω₂ parameter and Y/B ratio. The variation of decay time of ⁴F_9/2 emission level with the PbO content also supports the changes in structural asymmetry and DyO covalency in LBTAFDy glass.     

Growth of Pb on Si(3 3 5)–Au surface

The growth, crystallographic structure and electronic properties of ultrathin Pb films grown on a vicinal silicon surface are investigated with reflection high energy electron diffraction (RHEED) and specific resistivity measurement techniques. A Si(3 3 5) surface with a perfect distribution of monoatomic steps separated with (1 1 1) terraces induced by a submonolayer amount of Au is used as a substrate. In the early stage, Pb growth is anisotropic. Apparently, the presence of steps forces the growth of short crystalline Pb chains along the steps. The layer is amorphous in the perpendicular direction. With the increasing thickness, a phase transition takes place between 3 and 4 monolayers (ML) that makes crystalline order also across the terraces. A further increase in thickness causes the layer surface to repeat the substrate morphology. It consists of regularly distributed monoatomic steps and narrow (1 1 1) terraces.     

Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO₂–xBi₂O₃–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi₂O₃ content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi₂O₃ content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi_0.864Te_0.136O_1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.     

Effect of the ytterbium concentration on the upconversion luminescence of Yb3+/Er3+ co-doped PbO–GeO2–Ga2O3 glasses

The effect of Yb³⁺ concentration on the frequency upconversion (UPC) of Er³⁺ in PbO–GeO₂–Ga₂O₃ glasses is reported for the first time. Samples were prepared with 0.5 wt% of Er₂O₃ and different concentrations of Yb₂O₃ (1.0–5.0 wt%). The green (523 and 545 nm) and red (657 nm) emissions are observed under 980 nm diode laser excitation. The dependence of the frequency UPC emission intensity upon the excitation power was examined and the UPC mechanisms are discussed. An interesting characteristic of these glasses is the increase of the ratio of red to green emission, through an increase of the Yb³⁺ concentration due to an efficient energy transfer from Yb³⁺ to Er³⁺.     

3D Metal–Organic Framework Based on Cadmium Complex of Pyrazine-2,3,5,6-tetracarboxylic Acid

Abstract  

The 3D metal–organic framework based on cadmium complex of pyrazine-2,3,5,6-tetracarboxylate (pztc⁴⁻), {Cd₂(pztc)(H₂O)₂}_n, has been synthesized by the reaction of H₄pztc and Cd(NO₃)₂·4H₂O under hydrothermal conditions and characterized by elemental analysis, IR, single-crystal X-ray diffraction and fluorescence measurement. This complex belongs to triclinic system, P[`1] P\overline{1} space group with a = 5.0080(10) ?, b = 6.6578(13) ?, c = 8.5790(17) ?, α = 89.28(3)°, β = 75.76(3)°, γ = 78.80(3)°. All the donor N and O atoms in pztc⁴⁻ coordinate to Cd(II) ions. As decadentate ligand, each pztc⁴⁻ links eight Cd(II) atoms, which is a novel coordination mode of pztc⁴⁻.     

Effect of OH− content on emission properties in Er3+-doped tellurite glasses

A series of tellurite glasses of composition, 75TeO₂–20ZnO–(5 ? x)La₂O₃–xEr₂O₃ (x = 0.05, 0.1, 0.3, 0.6, 1.0, 2.0, and 3.0 mol%) with different hydroxl content were prepared. The effect of Er³⁺ and OH^? groups concentration on the emission properties of Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition in tellurite glasses was investigated. The constant K_OH–Er for Er³⁺ in tellurite glasses, which represents the strength of interaction between Er³⁺ and OH^? groups in the case of energy migration, was about 14 × 10^?19 cm⁴ s^?1. The interaction parameter C_Er,Er for the migration rate of Er³⁺: ⁴I_13/2 → ⁴I_13/2 transition in tellurite glass was 46 × 10^?40 cm², which indicates that concentration quenching in Er³⁺-doped modified tellurite glass for a given Er³⁺ concentration is much stronger than in silicate and phosphate glasses.     

Epitaxial Deposition of GaAs in the Ga(CH3)3?AsH3?H2 system (II). Investigations on the Hetero-Epitaxy of GaAs on Ge

Epitaxial GaAs layers have been deposited on (111), (110) and (100) faces of Ge by pyrolysis of Ga(CH₃)₃ AsH₃ H₂. In this paper the influence of growth conditions and the lattice difference of GaAs and Ge on the quality of epitaxial GaAs layers is described and discussed. The epitaxial layers are characterized by chemical etching, X-ray investigations, and by the observation of the surface morphology.     

Influence of cationic field strength of modifiers on the 1.53 μm spectroscopic properties of Er3+-doped tellurite glasses

Two series of Er³⁺-doped tellurite glasses with different glass modifiers were prepared by the conventional melt-quenching method. In order to estimate the effect of cationic field strength z/a² of modifiers on the fluorescence properties, the fluorescence spectra were measured. The strength parameters Ω_t (t = 2, 4, 6) for all the samples were calculated based on the absorption spectra and also compared between them. The values of Ω₆ decrease with decreasing of the cationic field strength z/a² of modifiers. As the cationic field strength decrease, the polarization effect of the ligand fields around Er³⁺ increase in the glasses, and which leads to the decreasing of fluorescence peak intensity and bandwidth. The strength of interactions between Er³⁺ ions and OH^? groups, k_OH–Er, depend on the glass composition, are changed with glass modifiers.     

Effect of TiO2 addition on the chemical durability of Bi2O3–SiO2–ZnO–B2O3 glass system

The effect of the substitution of ZnO for TiO₂ on the chemical durability of Bi₂O₃–SiO₂–ZnO–B₂O₃ glass coatings in hot acidic medium (0.1 N H₂SO₄ at 80 °C) for different times was studied. The thick films produced by a screen-printing method and heat treated at 700 °C/5 min were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The glass from the Bi₂O₃–SiO₂–ZnO–B₂O₃ system developed Zn₂SiO₄ and a glassy phase that were readily attacked by hot 0.1 N sulfuric acid, whereas the heat treated coating from the Bi₂O₃–SiO₂–TiO₂–ZnO–B₂O₃ system presented a finer microstructure with thin interconnected Bi₄Ti₃O₁₂ crystals and a glassy phase more resistant to hot 0.1 N sulfuric acid attack etching.     

Controlled Formation of β-Si3N4 on Native Oxidized Silicon Wafers in Ammonia Flow

Crystallography Reports - The formation of β-Si3N4 for subsequent growth of AlGaN and GaN heterostructures of silicon wafers has been studied. It is established that the native oxide layer...     

Synthesis of novel ester series and study of its mesomorphism dependence on terminal end group with lateral –OCH3 group

Novel liquid crystal (LC) materials of ester derivatives were synthesized and studied with a view to understanding and establishing the effects of molecular structure on LC properties. The novel molecules consist of two phenyl rings bonded through –COO– central group and a laterally substituted methoxy group with –OC_nH_2n+1 as well as –COOCH₃ terminal end groups, and yielded 12 homologous members of an ester series. The C₁ to C₃ members are nonmesomorphic, the C₄ to C₁₂ members are enantiotropic nematic only, and the C₁₄ to C₁₆ members are enantiotropically smectogenic in addition to nematogenic. Transition temperatures and the textures of LC state were observed through an optical polarizing microscope (POM) equipped with a heating stage. The textures of nematic phase are threaded or Schlieren, and that of smectic phase are focal conic of the type A or C. Transition curves of a phase diagram behave in normal manner with the exhibition of an odd-even effect (only N-I). Analytical and spectral data support the molecular structures of the novel ester derivatives. The LC properties of the present series are compared with structurally similar other known series. The average thermal stability of the series is 93°C for smectic and 120.88°C for nematic and the mesogenic phase length ranges between 2°C and 46°C.     

Effect of Al additive on the formation of cubic boron nitride in Li3N–hBN system under HPHT

We have investigated the effect of Al on cBN formation in Li₃N–hBN system at 5.0 GPa and 1300–1650 °C. Regular cBN single crystals of 0.2–0.5 mm in size were obtained. It appears that the presence of Al in hBN powder facilitates the formation of cBN crystals with regular shape, although it does not have any catalytic action for hBN–cBN phase transformation. With increasing Al concentration, the color of cBN changed darker from amber to black and the threshold temperature for cBN formation became higher. X-ray diffraction and Raman spectroscopy indicate that AlN formed by reaction of Li₃N and Al and some B liberated in system.     

Effects of the Li-evaporation on the Czochralski growth of γ-LiAlO2

Two-inch-diameter γ-LiAlO₂ single crystals were grown from the melt by Czochralski method. The crystals were examined by optical methods, high-resolution X-ray diffraction and transmission electron microscopy (TEM). Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the Li/Al ratio in the residual melts. The Li-evaporation from both melt and grown crystal is the main problem in the γ-LiAlO₂ growth and has to be controlled by acting on the vertical temperature gradient. Shallow gradients increase the Li-evaporation from the crystal surface resulting in boules with a milky rim. On the other hand, steep gradients may induce cracks in the boule and enhance the Li₂O escape from melt with consequent variation of the composition. ICP-OES investigations reveal that melt compositions can vary in the range from 46.5 to 50 mol% Li₂O to obtain transparent LiAlO₂ crystals. Beyond this value, the formation of inclusions inside the crystals is probable. We have established an optimized growth assembly, which allows remaining the melt composition stoichiometric. The as-grown crystals exhibit defects like subgrains, twins and a core of voids and fine-grained inclusions. The latter could be characterized by TEM as submicron LiAl₅O₈ crystallites.     

Influence of γ irradiation on the optical and mechanical properties of langasite

The optical (transmission and circular dichroism) spectra and mechanical (Vickers microhardness and fracture toughness K _1c ) properties of langasite La₃Ga₅SiO₁₄ crystals have been studied after γ irradiation and exposure for a month. It is shown that, as a result of irradiation crystals become more transparent in the range 310–640 nm, nonstructural defects with the energies of excited states in the range 2.06–4.13 eV decay and new structural defects with the excited-state energies in the range 4.14–5.00 eV are formed. Irradiation does not lead to a change in microhardness, while the coefficient K _1c increases from 0.32 to 0.36 MPa m^1/2.     

Influence of CH ⋅ ⋅ ⋅ O interactions on the structure of a pseudorotaxane based on an Hg(II) complex of 18-crown-6

The X-ray crystal structure of [Hg(NO₃)₂(18-crown-6)] (1) prepared from mercury(II) acetate and 18-crown-6 in nitric acid is reported. Crystals are monoclinic, space group P2₁/c with a = 8.3063(17) Å, b = 14.331(3) Å, c = 8.0030(16) Å, and = 99.528(3)°. In contrast to the usual perpendicular arrangement of the crown ether macrocycle mean plane and X–Hg–X in other Hg(II) crown ether complexes and related species, compound 1 shows a marked inclination as a result of a CH    O interactions.     

Characterization of the coordination network formed on self-assembly of 1,2-bis(3′-pyridyl)ethyne with copper(I) iodide

The self-assembly of 1,2-bis(3-pyridyl)ethyne with copper(I) iodide is described. The X-ray crystal structure of the resultant pale yellow crystalline solid reveals that the sheets of the two-dimensional coordination network are stacked such that channels are formed. The structure (C₁₂H₈Cu₂I₂N₂) is monoclinic with a = 9.285(2) Å, b = 4.1502(9) Å, c = 22.096(5) Å, = 97.380(11)°, and space group P2 ₁/c.     

Investigation of the Mechanism of Influence of Stress Corrosion on the Development of Macroplastic Instabilities of Aluminum–Magnesium Alloy

Crystallography Reports - Macroscopic jumps of plastic deformation (few percent in amplitude) on creep curves of aluminum–magnesium alloy, caused by a local effect of concentrated solution of...     

Effect of alumina on the structure and properties of Li2O–B2O3–P2O5 glasses

The structure of glasses within the system Li₂O–Al₂O₃–B₂O₃–P₂O₅ has been studied through ³¹P, ¹¹B and ²⁷Al Nuclear Magnetic Resonance, and the effect of Al₂O₃ substitution by B₂O₃ and P₂O₅ network formers on the structure and properties investigated for a constant Li₂O content. Multinuclear NMR results reveal that substitution of Al₂O₃ for B₂O₃ and P₂O₅ network formers in a glass with composition 50Li₂O·15B₂O₃·35P₂O₅ produces a change in boron environment from four-fold to three-fold coordination. Meanwhile aluminum can be present in four-, five- and six-fold coordinations a higher amount of Al(IV) groups is found for increasing alumina contents. The behavior of the glass transition temperature and electrical conductivity of the glasses has been interpreted as a function of the structural changes induced in the glass network when alumina is substituted for B₂O₃, P₂O₅ or both. Small additions of alumina produce a drastic increase in glass transition temperature, while it does not change for [Al₂O₃] greater than 3 mol.%. However, the electrical conductivity shows very different behavior depending on the type of substitution; it can remain constant when B₂O₃ content decreases or sharply decrease when P₂O₅ is substituted by Al₂O₃, which is attributed to a higher amount of BO₃ and phase separation.