http://hdl.handle.net/10316/27722 2020-03-07T13:36:27Z http://hdl.handle.net/10316/27827 Title: Highly fluorinated erbium(III) complexes for emission in the C-band Authors: Martín-Ramos, P.; Ramos Silva, M.; Lahoz, F.; Martín, I. R.; Chamorro-Posada, P.; Eusebio, M. E. S.; Lavín, V.; Martín-Gil, J. Abstract: Two highly fluorinated Er3+ complexes with three 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate (fod) groups and either bipyridine (bipy) or bathophenantholine (bath) as the ancillary ligand emitting at the C-band (third communication window for fiber transmission) are presented. These complexes are the result of a design process aimed at decreasing the vibrational quenching from high frequency oscillators. The structure of [Er(fod)3(bipy)] has been elucidated by single-crystal X-ray diffraction, while Sparkle/PM6 and Sparkle/PM7 semi-empirical calculations have been used to model the ground state geometry for [Er(fod)3(bath)]. Photoluminescence studies confirm sensitization of the Er3+ ions by antenna effect, leading to NIR emission at 1.53 μm. This energy transfer proves to be more efficient for [Er(fod)3(bath)] as a result of the bulkier and more rigid structure of bath diimide. The good thermal stability of the materials up to over 200 °C allows envisaging their use in erbium-doped waveguides, NIR-OLEDs or other optoelectronic devices. 2014-10-15T00:00:00Z http://hdl.handle.net/10316/27723 Title: Formation stages of bcc (Fe44Co44)Sn12 extended solid solution by mechanical alloying Authors: Loureiro, J. M.; Costa, B. F. O.; Malaman, B.; Caër, G. Le; Das, S.; Amaral, V. S. Abstract: The synthesis of supersaturated bcc Fe44Co44Sn12 by mechanical alloying was followed by various techniques. Two stannides, CoSn5 and FeSn2 form first at interfaces. Tetragonal CoSn5, a very recently discovered stannide, is obtained here by a simple method. These stannides then dissolve and the ternary bcc alloy forms with a progressive and simultaneous dissolution of Co and Sn into bcc Fe. 2014-01-01T00:00:00Z http://hdl.handle.net/10316/27649 Title: Molecular structure and polymorphism of a cyclohexanediol: trans-1,4-cyclohexanedimethanol Authors: Rosado, Mário T. S.; Maria, Teresa M. R.; Castro, Ricardo A. E.; Canotilho, João; Silva, Manuela Ramos; Eusébio, M. Ermelinda S. Abstract: This study aims to investigate the molecular structure and polymorphism of trans-1,4-cyclohexanedimethanol, including the bi-axial/bi-equatorial equilibrium and the nature of the intermolecular H-bond networks in condensed phases created by the hydroxyl group torsions. The full conformational space of the single molecule was explored by MP2 calculations, showing that the optimized bi-equatorial conformers have similar stability and the bi-axial ones have much higher energies. The hydroxymethyl substituents have preference for gauche/anti or gauche+/gauche− conformations. Polymorphic forms were generated by crystallization from solutions and by cooling the melt, which were characterized by a combination of techniques: DSC, PLTM and XRD. Two polymorphs were isolated and their crystal structures were solved by direct methods based on single-crystal X-ray analysis. Both were found to contain two of the most stable conformers found in the computational calculations. The influence of H-bonding in the polymorphic structures was verified by analysis of the structural differences between the geometries present in the polymorphs determined by XRD and their single molecule counterparts resulting from the theoretical calculations. The bi-axial conformations are destabilized over the bi-equatorial ones in isolated and crystalline forms of trans-1,4-cyclohexanedimethanol. 2014-10-01T00:00:00Z http://hdl.handle.net/10316/27120 Title: Experimental and theoretical studies of the second- and third-order NLO properties of a semi-organic compound: 6-Aminoquinolinium iodide monohydrate Authors: Silva, Pedro S. Pereira; Ouazzani, Hasnaa El; Pranaitis, Mindaugas; Silva, Manuela Ramos; Arranja, Cláudia T.; Sobral, Abilio J. F. N.; Sahraoui, Bouchta; Paixão, José A. Abstract: A new semi-organic compound, 6-aminoquinolinium iodide monohydrate (I), has been synthesized and characterized by single crystal X-ray diffraction, UV–vis absorption and fluorescence spectroscopy and nonlinear optical (NLO) measurements. The second- and third-order NLO responses were investigated with the second- and third-harmonic Maker fringes techniques, carried out on thin films at a fundamental wavelength of 1064 nm. From the molecular structure, the molecular hyperpolarizability tensors were determined with density functional theory and second-order Møller–Plesset perturbation method. The second- and third-order susceptibility tensors of the reported crystal were evaluated using the oriented gas model with the Lorenz–Lorentz and the Wortmann–Bishop local-field corrections. The calculations using the Wortmann–Bishop local-field were able to reproduce the correct order of magnitude of the experimental third-order susceptibilities. The value of χ(3) obtained by summing the effective third-order polarizability calculated for the asymmetric unit surrounded by ESP-derived charges have also the same order of magnitude of the experimental. 2014-01-15T00:00:00Z