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Kumar M.V.V.,Sri Krishnadevaraya University | Gopal K.R.,Sri Krishnadevaraya University | Reddy R.R.,Sri Krishnadevaraya University | Reddy G.V.L.,Government Degree College | And 2 more authors.
Journal of Non-Crystalline Solids | Year: 2013

Praseodymium doped lead telluroborate (PTBPr) glasses were prepared by conventional melt quenching method. The absorption spectra have been analyzed to evaluate the intensity parameters applying the standard and the modified Judd-Ofelt theories. The emission spectra under 3P2 level excitation (λex = 447 nm) were investigated to estimate the laser characteristic parameters. These emission measurements together with Judd-Ofelt intensity parameters (λ = 2,4,6) have been used to calculate the radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of the transitions from 3P0 and 1D2 levels to their lower lying levels. The quenching of fluorescence intensity and experimental lifetime with the increase of Pr 3 + concentration and the shift of 1D2 → 3H4 emission peak towards longer wavelengths was discussed. The non-radiative losses due to multiphonon and energy transfer relaxations were also explained. The Commission Internationale de I'Eclairage (CIE) coordinates, color purity and optical band gap energy values were evaluated. Some of the basic laser characteristics such as stimulated emission cross-section, optical and bandwidth gain parameters and fluorescence quantum efficiency were also reported. © 2012 Elsevier B.V.

Wack J.,University of Bayreuth | Siegel R.,University of Bayreuth | Ahnfeldt T.,University of Bayreuth | Ahnfeldt T.,University of Kiel | And 3 more authors.
Journal of Physical Chemistry C | Year: 2013

We present a study analyzing the selectivity of host-guest interactions in a series of functionalized Al-MIL-53-X metal-organic frameworks with X = H, NH2, and NHCHO using acetone, ethanol, and water as probe molecules. While the amino group introduces additional hydrogen bond donor centers the NHCHO anchors function as donor and acceptor. The guests were chosen due to their ability to act solely as an acceptor in the case of acetone, whereas ethanol and water provide acceptor and donor qualities with a gradual decrease of the acceptor strength toward ethanol. The characterization of the host-guest interactions includes a comprehensive solid-state NMR spectroscopic study based on a full assignment of 1H and 13C high-resolution spectra using CRAMPS decoupling schemes to enhance 1H resolution combined with advanced 2D HETCOR (1H-13C, 1H- 27Al, and 1H-14N) spectra at high magnetic fields. In spite of a pronounced dynamical disorder of the guests, we could identify a preferred binding of the acetone via a NH···OC hydrogen bond for the NH2 and the NHCHO anchor groups by analyzing trends in the 13C isotropic chemical shifts. At the same time 1H-1H through-space connectivities reveal a close vicinity of the acetone methyl groups to the benzene rings of the linkers. In contrast, for ethanol and water, the interaction with the anchor groups is too weak to compete with the thermal disorder at room temperature. © 2013 American Chemical Society.

Gautam U.K.,Japan International Center for Materials Nanoarchitectonics | Costa P.M.F.J.,CICECO | Bando Y.,Japan International Center for Materials Nanoarchitectonics | Fang X.,Japan International Center for Materials Nanoarchitectonics | And 3 more authors.
Science and Technology of Advanced Materials | Year: 2010

Carbon nanotubes (CNTs) are a unique class of nanomaterials that can be imagined as rolled graphene sheets. The inner hollow of a CNT provides an extremely small, one-dimensional space for storage of materials. In the last decade, enormous effort has been spent to produce filled CNTs that combine the properties of both the host CNT and the guest filling material. CNTs filled with various inorganic materials such as metals, alloys, semiconductors and insulators have been obtained using different synthesis approaches including capillary filling and chemical vapor deposition. Recently, several potential applications have emerged for these materials, such as the measurement of temperature at the nanoscale, nano-spot welding, and the storage and delivery of extremely small quantities of materials. A clear distinction between this class of materials and other nanostructures is the existence of an enormous interfacial area between the CNT and the filling matter. Theoretical investigations have shown that the lattice mismatch and strong exchange interaction of CNTs with the guest material across the interface should result in reordering of the guest crystal structure and passivation of the surface dangling bonds and thus yielding new and interesting physical properties. Despite preliminary successes, there remain many challenges in realizing applications of CNTs filled with inorganic materials, such as a comprehensive understanding of their growth and physical properties and control of their structural parameters. In this article, we overview research on filled CNT nanomaterials with special emphasis on recent progress and key achievements. We also discuss the future scope and the key challenges emerging out of a decade of intensive research on these fascinating materials. © 2010 National Institute for Materials Science.

Santos L.M.N.B.F.,University of Porto | Rocha M.A.A.,University of Porto | Gomes L.R.,Fernando Pessoa University | Gomes L.R.,University of Porto | And 2 more authors.
Journal of Chemical and Engineering Data | Year: 2010

The gaseous phase heat capacity of benzoic acid (BA) was proven using the experimental technique called the "in vacuum sublimation/vaporization Calvet microcalorimetry drop method". To overcome known experimental shortfalls, the gaseous phase heat capacity of BA monomer was estimated by ab initio calculations and compared with experimental results. Gaseous phase heat capacities of BA were directly derived via calculated harmonic frequencies obtained by density functional theory (DFT) (B3LYP, BLYP, BP86, with 6-311++G(d,p), TZVP, cc-pVTZ basis sets) and the second-order Møller-Plesset theory, MP2/6-311++G(d,p). To increase the accuracy of estimation of the thermal properties, a procedure based on the calculation of the heat capacity from quantum chemical calculations in combination with a heat capacity balance of isodesmic reactions is described and applied to calculate the gaseous phase heat capacity, Cp,m, of the monomeric species over the temperature range of (298.15 to 600) K. The gaseous phase thermodynamic properties of the monomeric form of the BA were also derived from the assignment of the fundamental vibrational frequencies using experimental IR spectra. An excellent agreement among the experimental gaseous phase heat capacities, the results obtained using the proposed ab initio procedure, and the results derived from the assignment of fundamental vibrational frequencies was found. The results for the monomeric form of the BA, directly or indirectly obtained, and conclusions of this work strongly support the thesis that the gaseous phase heat capacity data as currently found in the literature are underestimated to the order of 20 %. © 2010 American Chemical Society.

Cui X.,New University of Lisbon | Delgado R.,New University of Lisbon | Delgado R.,University of Lisbon | Costa J.,CBT iMed.UL | And 3 more authors.
Polyhedron | Year: 2010

The rigid [6]ferrocenophane, L1, was synthesised by condensation of 1,1′-ferrocene dicarbaldehyde with trans-1,2-diaminocyclohexane in high dilution at r.t. followed by reduction. When other experimental conditions were employed, the [6,6,6]ferrocenephane (L2) was also obtained. Both compounds were characterised by single crystal X-ray crystallography. The protonation of L1 and its metal complexation were evaluated by the effect on the electron-transfer process of the ferrocene (fc) unit of L1 using cyclic voltammetry (CV) and square wave voltammetry (SWV) in anhydrous CH3CN solution and in 0.1 M nBu4NPF6 as the supporting electrolyte. The electrochemical process of L1 between -300 and 900 mV is complicated by amine oxidation. On the other hand, an anodic shift from the fc/fc+ wave of L1 of 249, 225, 81 and 61 mV was observed by formation of Zn2+, Ni2+, Pd2+ and Cu2+ complexes, respectively. Whereas Mg2+ and Ca2+ only have with L1 weak interactions and they promote the acid-base equilibrium of L1. This reveals that L1 is an interesting molecular redox sensor for detection of Zn2+ and Ni2+, although the kinetics of the Zn2+ complex formation is much faster than that of the Ni2+ one. The X-ray crystal structure of [PdL1Cl2] was determined and showed a square-planar environment with Pd(II) and Fe(II) centres separated by 3.781(1) Å. The experimental anodic shifts were elucidated by DFT calculations on the [ML1Cl2] series and they are related to the nature of the HOMO of these complexes and a four-electron, two-orbital interaction. © 2010 Elsevier Ltd. All rights reserved.

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