Spectroscopic and photoluminescence characteristics of Dy ions in lead containing sodium fluoroborate glasses for laser materials

Lead containing calcium zinc sodium fluoroborate (LCZSFB) glasses doped with different concentrations of trivalent dysprosium ions were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. The experimentally determined oscillator strengths have been determined by measuring the areas under the absorption peaks and the Judd–Ofelt (J–O) intensity parameters were calculated using the least squares fit method. From the evaluated J–O parameters the radiative transition probability rates, radiative lifetimes and branching ratios were calculated for ⁴F_9/2 excited level. Room temperature photoluminescence spectra for different concentrations of Dy³⁺-doped LCZSFB glasses were obtained by exciting the glass samples at 386 nm. The intensity of Dy³⁺ emission spectra increases with increasing concentration of 0.1, 0.25, 0.5 and 1.0 mol% and beyond 1.0 mol% the concentration quenching is observed. The measuring branching ratios are reasonably high for transitions ⁴F_9/2→⁶H_15/2 and ⁶H_13/2, suggesting that the emission at 484 and 576 nm, respectively, can give rise to lasing action in the visible region. From the visible emission spectra, yellow–blue (Y/B) intensity ratios and chromaticity color coordinates were also estimated. The lifetimes of ⁴F_9/2 metastable state for the samples with different concentrations were also measured and discussed.     

Laser Desorption Ionization of As<Subscript>2</Subscript>Ch<Subscript>3</Subscript> (Ch = S,Se, and Te) Chalcogenides Using Quadrupole Ion Trap Time-of-Flight Mass Spectrometry: A Comparative Study

Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As₂Ch₃ (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (S _p ^+/– and As _m ^+/– ) and 34 binary (As _m S _p ^+/– ) species for As₂S₃ glass, 2 unary (Se _q ^+/– ) and 26 binary (As _m Se _q ^+/– ) species for As₂Se₃ glass, 7 unary (Te _r ^+/– ) and 23 binary (As _m Te _r ^+/– ) species for As₂Te₃ material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials.

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Theory of the transverse static magnetoconductivity in a two-dimensional electron-phonon system

The theory of the transverse static magnetoconductivity (σ_xx) in a two-dimensional system under the simultaneous influence of electron-phonon and electron-impurity interactions is presented. The memory function technique is employed to obtain explicit expression for σ_xx under conditions appropriate for typical Shubnikov-deHaas measurements. It is shown that σ_xx involves two different effective masses and scattering times, of which one is the scattering time in the absence of the magnetic field. In addition, the Landau level width appears in σ_xx, thus providing an experimental means for extracting the same from a study of the background conductivity.     

Chemisorption bonding and bond lengths on transition metal surfaces: Effect of coordination and valency saturation

A smooth correlation between the determined chemisorption bond lengths, for O, S, Se and Te on Ni (001) and for sulphur on Ni (110) and Ni (111) as well, and Pauling's resonating bond ionicity is demonstrated, when the latter are calculated with due regard for the coordination and valency saturation effects. Pauling's bond length-bond number relation is used to provide (i) an independent estimate of the Ni-O bond length on Ni (001), which is found capable of discriminating among the reported values, and (ii) estimates of the bond lengths for O, S, Se and Te on Ni (111) and Ni (110) by using the determined bond lengths on Ni (001). Agreement with the determined values for sulphur is surprisingly good.     

Bistable characteristics of thick-walled axisymmetric domes

We apply a finite element analysis to examine the stability of spherical, thick-walled domes undergoing large deformation. We identify three energetic states, mono-stable, bi-stable, and pseudo-bi-stable that uniquely characterize the behavior of the dome during deformation. An empirical relation is developed using finite element simulations relating the stability of the dome to pertinent geometric parameters like height, length and thickness, which is verified experimentally. Using this relation, similar domes can be designed to have desired stability characteristics.     

In-situ fabrication of three-dimensionally confined GaAs and InAs volumes via growth on non-planar patterned GaAs(001) substrates

Three-dimensionally confined GaAs/AlGaAs and InAs/GaAs structures on 100 oriented square mesas patterned onto GaAs(001) substrates are realized, in-situ, via size-reducing molecular beam epitaxy. Two stages of mesa top pinch-off involving {103} and subsequently {101} side facets are revealed. GaAs and InAs quantum boxes with lateral linear dimensions down to 40 nm and confined by AlGaAs and GaAs, respectively, are reported. For InAs, the strain relief in mesas is found to enhance the well known 2 ML thickness for three-dimensional island formation on unpatterned substrates to, remarkably, >5 ML for mesa size 75 nm. Cathodoluminescence emission from the InAs on the mesa top attests to its good optical quality.     

An efficient synthesis of pyrazolo[3,4‐b]pyrrolo[2,3‐d]pyridines from 5‐aminopyrazoles and cyclic β‐keto ester

5‐Chloroethylpyrazolo[3,4‐b]pyridines were synthesized by condensation of 5‐aminopyrazoles with α‐acetyl γ‐butyrolactone followed by cyclization treating with phosphorous oxychloride. 5‐Chloroethyl‐pyrazolo[3,4‐b]pyridines, thus obtained, were then converted to the corresponded tricyclic pyrazolo[3,4‐b]‐pyrrolo[2,3‐d]pyridines by treating with some primary amines.     

A new supramolecular cocrystal of 2-amino-3-bromopyridine with 4-methylbenzoic acid: Synthesis,structural, spectroscopic characterization and comparative theoretical studies

The 1:1 cocrystal of 2-amino-3-bromopyridine (2A3BP) with 4-methylbenzoic acid (4MBA) has been prepared by slow evaporation method in methanol, which was crystallized in monoclinic P2₁/c space group having two molecules in the asymmetric unit. The cocrystal has been characterized by single crystal X-ray analysis, FTIR, ¹H NMR, ¹³C NMR, and Powder XRD. Theoretical investigations have been calculated by HF and density function (B3LYP) method with the 6-311+G(d,p) basis set. The vibrational frequencies together with the ¹H NMR and ¹³C NMR chemical shifts have been calculated on the fully optimized geometry of 1. Theoretical calculations of bond parameters, harmonic vibration frequencies, and isotropic chemical shifts are in good agreement with the experimental results. Solvent-free formation of these cocrystal was confirmed by powder X-ray diffraction analysis. The crystal structure was stabilized by N_pyridine—H···O = C, C = O—H···N_pyridine and C—H···Br hydrogen bonding interactions.