Theo Woike

University of Lorraine, Nancy, Lorraine, France

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Publications (92)183.12 Total impact

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    ABSTRACT: We observed a multiphoton luminescence contrast between virgin and single-switched domains in Mg-doped LiNbO3 (LNO) and LiTaO3 (LTO) single crystals with different doping levels of 0–7 mol. % and 0–8 mol. %, respectively. A luminescence contrast in the range of 3% was measured between as-grown and electrically inverted domain areas in Mg:LNO samples, while the contrast reaches values of up to 30% for the Mg:LTO case. Under annealing, an exponential decay of the do- main contrast was observed. The activation energy of about 1 eV being determined for the decay allowed a comparison with reported activation energies of associated defects, clearly illustrating a strong connection between thermal contrast decay and the Hþ and Liþ-ion mobility. Finally, per- forming similar experiments on oxidized samples undoubtedly demonstrated that the origin of the reported luminescence contrast is strongly connected with lithium ions.
    Applied Physics Letters 09/2014; 12(105):122906. · 3.52 Impact Factor
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    ABSTRACT: Two different structure types were found for a series of mononuclear dinitrosyl complexes of the general formula [RuL2(NO)2X]BF4 (L = monodentate phosphane, X = Cl, Br, I). The {Ru(NO)2}(8)-type target compounds were prepared by the reduction of the respective {RuNO}(6) precursors and subsequent oxidative addition of (NO)BF4. About one half of the new compounds share their molecular structure with the hitherto only representative of this class of dinitrosyls, Pierpont and Eisenberg's [RuCl(NO)2(PPh3)2]PF6·C6H6 (Inorg. Chem., 1972, 11, 1088-1094). The Cs-symmetric cations exhibit both a linear and a bent Ru-N-O fragment, in line with a formal 6 + 2 split of the {Ru(NO)2}(8) electron sum in the sense of a [Ru(II)(NO(+))((1)NO(-))](2+) bonding. The coordination entity's configuration in this subgroup is described by IUPAC's polyhedral symbol SPY-5. Continuous shape measures (CShM) as defined by Alvarez et al. (Coord. Chem. Rev., 2005, 249, 1693-1708) reveal a uniform deviation from the L-M-L angles expected for SPY-5, in a narrower sense, towards a vacant octahedron (vOC-5). DFT calculations confirmed that Enemark and Feltham's analysis (Coord. Chem. Rev., 1974, 13, 339-406) of the electronic situation of the {Ru(NO)2}(8) group remains adequate. The same holds for the second subclass of new compounds the existence of which had been predicted in the same paper by Enemark and Feltham, namely C2v-symmetric, TBPY-5-type cations with two almost equally bonded nitrosyl ligands. In agreement with an 8 + 0 distribution of the relevant electrons, the formal [Ru(0)(NO(+))2](2+) entities are found for L/X couples that donate more electron density on the central metal. Two solid compounds (/, /) were found in both structures including the special case of the P(i)Pr3/Br couple /, which led to crystals that contained both structure types in the same solid. Conversely, four compounds showed a single form in the solid but both forms in dichloromethane solution in terms of the solutions' IR spectra. The irradiation of crystalline with blue laser light resulted in the photoisomerisation of, mainly, the bent (1)NO(-) ligand in terms of low-temperature IR spectroscopy.
    Dalton Transactions 07/2014; · 4.10 Impact Factor
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    ABSTRACT: Cherenkov second-harmonic generation (CSHG) is a powerful tool for three-dimensional domain wall profiling in ferroic bulk crystals. Here, we apply this noninvasive technique for tracking head-to-head charged domain walls (CDWs) across millimeter-thick ferroelectric single-crystalline lithium niobate. CSHG sensitively reveals the inclination α >0 of any such CDW with a superb optical resolution. Moreover, we deduce fully charged head-to-head CDWs (α = 90∘) to be much rougher and to show protrusions, domain inclusions, and novel topologies. Our findings provide insight into the mechanisms of electron transport and charge trapping in CDWs, as is mandatory for their use in prospective nanoelectronic devices.
    Physical Review B 01/2014; 89(3):035314. · 3.66 Impact Factor
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    ABSTRACT: We report on differentiating antiparallel ferroelectric domains in congruent Mg-doped LiNbO3 (Mg:LNO) single crystals through a multiphoton photoluminescence technique. Sample illumination with femtosecond laser pulses at λ = 790 nm results in a broad multiphoton emission spectrum revealing a domain contrast of >3% between virgin and inverted domains. The contrast decreases via annealing and shows an exponential decay in the temperature range from 80 to 150 °C. Our findings give clear ground of a thermally induced structural change by surpassing a specific activation energy. Hence, the reported contrast dynamics must be closely connected to the thermal activation of charged defects, which dramatically alters the internal bias field of these defects. This explanation is also supported when using single crystal LNO of different Mg doping levels showing much lower multiphoton effects for a < 5% Mg concentration. Based on this effect of multiphoton luminescence, it becomes easy to microscopically monitor and quantify virgin and switched domains in LNO and other samples.
    Journal of Applied Physics 01/2014; 115(21):213509-213509-5. · 2.21 Impact Factor
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    ABSTRACT: We present an experimental approach to study the structure and dynamics of molecular functional complexes in porous host matrices. Combining the results of Solid-State NMR and pair distribution function analysis based on total X-ray scattering data the structural arrangement and dynamical behaviour of Na2[Fe(CN)5NO]$2H2O (SNP) embedded in amorphous SiO2 matrix is investigated. We show that the SNP complexes are embedded as isolated complexes within the SiO2 pores and propose a structural model for the cation and anion arrangement. Additionally the NMR results demonstrate the rotational dynamics of the SNP complexes.
    RSC Advances 10/2013; 3(48):26132-26141. · 3.71 Impact Factor
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    ABSTRACT: The structure of the photoluminescent compound hexaaquadichloridoneodymium(III) chloride has been redetermined from single-crystal X-ray diffraction data at 100 K, with the aim of providing an accurate structural model for the bulk crystalline material. The crystal structure may be described as a network of [NdCl2(H2O)6](+) cations with distorted square-antiprism geometry around the Nd(III) centre. The Nd(III) cation and the nonbonded Cl(-) anion are both located on twofold symmetry axes. The crystal packing consists of three different neodymium pairs linked by a three-dimensional network of O-H...Cl intermolecular interactions. The pair distribution function (PDF) calculated from the experimentally determined structure is used for the discussion of the local structure.
    Acta Crystallographica Section C Crystal Structure Communications 09/2013; 69(Pt 9):1002-5. · 0.78 Impact Factor
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    ABSTRACT: UV–Vis- and infrared femtosecond spectroscopy makes it possible to reveal all different steps of photochemical reactions after the electronic excitation. The electronic relaxations are observed in the UV–Vis spectral range whereas the nuclear motions are monitored in the infrared spectral range. We used femtosecond time-resolved infrared spectroscopy to demonstrate the photoisomerization of the NO ligand photoinduced by a visible femtosecond pulse in a Na2[Fe(CN)5NO]·2H2O single crystal occurs in about 350 fs. The analysis of data makes it possible to unravel the mechanism leading to the photoisomerization of the NO ligand.
    Chemical Physics Letters 11/2012; 552:64–68. · 2.15 Impact Factor
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  • Advanced Functional Materials 09/2012; 22(18). · 10.44 Impact Factor
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    ABSTRACT: In mononitrosyl complexes of transition metals two long-lived metastable states corresponding to linkage isomers of the nitrosyl ligand can be induced by irradiation with appropriate wavelengths. Upon irradiation, the N-bound nitrosyl ligand (ground state, GS) turns into two different conformations: isonitrosyl O bound for the metastable state 1 (MS1) and a side-on nitrosyl conformation for the metastable state 2 (MS2). Structural and spectroscopic investigations on [RuCl(NO)py(4)](PF(6))(2)·1/2H(2)O (py = pyridine) reveal a nearly 100% conversion from GS to MS1. In order to identify the factors which lead to this outstanding photochromic response we study in this work the influence of counteranions, trans ligands to the NO and equatorial ligands on the conversion efficiency: [RuX(NO)py(4)]Y(2)·nH(2)O (X = Cl and Y = PF(6)(-) (1), BF(4)(-) (2), Br(-)(3), Cl(-) (4); X = Br and Y = PF(6)(-) (5), BF(4)(-) (6), Br(-)(7)) and [RuCl(NO)bpy(2)](PF(6))(2) (8), [RuCl(2)(NO)tpy](PF(6)) (9), and [Ru(H(2)O)(NO)bpy(2)](PF(6))(3) (10) (bpy = 2,2'-bipyridine; tpy = 2,2':6',2"-terpyridine). Structural and infrared spectroscopic investigations show that the shorter the distance between the counterion and the NO ligand the higher the population of the photoinduced metastable linkage isomers. DFT calculations have been performed to confirm the influence of the counterions. Additionally, we found that the lower the donating character of the ligand trans to NO the higher the photoconversion yield.
    Inorganic Chemistry 07/2012; 51(14):7492-501. · 4.59 Impact Factor
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    ABSTRACT: We study the properties of photoinduced metal-nitrosyl linkage isomers in sodium nitroprusside (SNP) as a function of particle size. By embedding the molecular complex at various concentrations into mesopores of silica xerogels the size of the particles can be adjusted. The ground state is characterized by X-ray diffraction, absorption and infrared spectroscopy. The physical properties of the photoswitched molecules were analysed by steady-state low-temperature absorption, infrared spectroscopy and by nanosecond transient absorption spectroscopy. The electronic structure as well as the activation energies of the metastable linkage isomers are independent of the particle size down to single isolated molecules, indicating that the SNP complexes are quasi-free inside the pores of the gel.
    Physical Chemistry Chemical Physics 02/2012; 14(11):3775-81. · 4.20 Impact Factor
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    ABSTRACT: We report on the improvement in photostability of solid-state dye materials. The photostability is the amount of energy that can be deposited in the material before its luminescence or lasing intensity has dropped to 50% of the initial value. It is shown that the photostability can be prolonged by a factor 100 by reducing the oxygen content in the material. The realized oxygen removal procedure and encapsulation of the solid state dye does not affect the luminescence properties and thus might be applicable in dye lasers.
    Optical Materials Express 01/2012; 2(1). · 2.92 Impact Factor
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    ABSTRACT: Single photoswitchable molecules of (CN3H6)2[Fe(CN)5NO] (GuNP) are embedded into nanopores of an SiO2 xerogel. It is shown that it is possible to identify the structural motif (`fingerprint') of the embedded complex by analyzing neutron powder diffraction data in a limited Q range (Q < 37 nm−1) using the Debye approach. The structural study reveals that the pores are occupied by GuNP monomers with a fill factor of 60–80%. The mutual arrangement of the anion and cations in the GuNP monomer is slightly changed (∼1% elongation), while the bond lengths within the anion and cation are changed by less than 0.2% with respect to the single-crystalline form of GuNP.
    Journal of Applied Crystallography 10/2010; 43(5). · 3.34 Impact Factor
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    ABSTRACT: We present a time-resolved absorption study on the light-induced generation of reversible linkage NO isomers in single crystals of Na(2)[Fe(CN)(5)NO] x 2 H(2)O using laser pulses of 160 fs width. Using the pump wavelength lambda = 500 nm the singlet-singlet (1)A(1)-->(1)E excitation induces the NO rotation by about 90 degrees from the linear Fe-N-O configuration to a side-on configuration [structure: see text]. The formation of the isomer is monoexponential with a characteristic time of tau = 300(20) fs and proceeds along a diabatic potential surface without occupation of further intermediate states. The side-on structure has a lifetime of 270(30) ns at T = 23 degrees C.
    Physical Chemistry Chemical Physics 08/2010; 12(31):9029-33. · 4.20 Impact Factor
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    ABSTRACT: The electrochemistry of the complex [Fe(CO)2(NO)2] and the IR and EPR spectra of the one-electron reduced [Fe(CO)2(NO)2]- and one-electron oxidised species [Fe(CO)2(NO)2]+ reveal mainly NO-centred spin density for the unpaired electron. The results are discussed in term of oxidation states. Furthermore, the parent complex was investigated for light-induced linkage isomerisation using IR spectroscopy. Thermally and optically reversible generation of a new species identified by new vibrational bands is interpreted in terms of photoinduced nitrosyl linkage isomers.
    Polyhedron 07/2010; 29(12):2553-2559. · 2.05 Impact Factor
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    ABSTRACT: Nitro-nitrito photoisomerisation is investigated in solid samples and solutions of trans-[Ru(py)(4)(NO(2))(2)]. Using light of wavelength 325 nm 50% of the N-bound Ru-NO(2) ligands can be switched to the O-bound Ru-ONO configuration (nitrito-N to nitrito-O isomerisation) at temperatures below T = 250 K in solids. The population of the isomeric configurations is determined with infrared spectroscopy from the decrease of the area of the nu(NO) stretching and delta(NO) deformation modes. In a frozen methanol-ethanol solution nearly 100% can be converted to the nitrito-O configuration. Upon heating above T = 250 K the Ru-NO(2) configuration is restored. The nitrito-O Ru-ONO configuration can be partially transferred back to the nitrito-N configuration by irradiation with light in the spectral range 405-442 nm. Using absorption spectroscopy on a frozen methanol-ethanol solution, two new bands at 447 and 380 nm are observed in the nitrito-O configuration compared to one at 334 nm of the nitrito-N ground state configuration. The photoconversion is initiated by the metal-to ligand charge transfer transition Ru(d) -->pi*(NO(2),py) as shown by the calculated partial density of states using Density Functional Theory. The calculations yield also the structure of the nitrito-N and nitrito-O isomer as well as the corresponding vibrational densities. The experimental structure of the ground state is determined using powder diffraction.
    Physical Chemistry Chemical Physics 04/2010; 12(23):6171-8. · 4.20 Impact Factor
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    ABSTRACT: Phototriggered NO and CN release from [Fe(CN)(5)NO](2-) (NP) molecular monolayers is studied by a combination of electrochemistry, infrared spectroscopy, and mass spectrometry under light irradiation at temperatures of 80 K and 294 K. The NP molecular monolayers were electrostatically attached to thin films of mesoporous TiO(2) deposited on silicon. Irradiation of the surfaces results in NO and CN release, which is verified using mass spectrometry. The kinetic trace of the light driven NO release of the [Fe(CN)(5)NO](2-) is determined by inspection of the nu(NO) stretching mode as a function of exposure to light in the violet/green spectral range. The decrease of the nu(NO)-amplitude can be modeled considering the NO release as a two-step process with an intermediate state between the attached and the released state. According to literature, the intermediate state may be related to the light-induced linkage NO isomerization of the NP.
    Physical Chemistry Chemical Physics 04/2010; 12(13):3283-8. · 4.20 Impact Factor
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    ABSTRACT: Second-harmonic generation (SHG) in polycrystalline and porous LiTaO3LiTaO3- and LiNbO3LiNbO3-xerogels is reported. The ferroelectric xerogels are synthesized via the sol–gel method and sintered at different temperatures of 700 °C, 900 °C, 1100 °C and 1150 °C, respectively for 48 h. The nano-structured materials (grain size of 250–1760 nm) are characterized by scanning electron microscopy, thermogravimetry, X-ray diffraction and piezoresponse force microscopy. The ferroelectricity of the grains is determined with piezoresponse force microscopy measurements. While the SHG efficiency grows with increasing grain size, the SHG output energy increases with a higher grade of stoichiometry and increases quadratically as a function of the input energy.
    Optical Materials 02/2010; 32(4):504–509. · 2.08 Impact Factor
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    ABSTRACT: Two different kinds of short-lived phase gratings are written with identically and orthogonally polarized waves using nanosecond laser pulses in single crystals of the nitrosyl compounds Na 2 [ Fe ( CN ) 5 NO ] ⋅ 2 H 2 O , ( CN 3 H 6 ) 2 [ Fe ( CN ) 5 NO ] , and Ba [ Fe ( CN ) 5 NO ] ⋅ 3 H 2 O . With identically polarized recording beams thermal gratings are written by the thermo-optic effect, which results from the spatially modulated thermo-optic coefficient ∂ n / ∂ T . The lifetime τ dif of such gratings depends quadratically on the spatial grating frequency K with the thermal diffusion coefficient D dif as the material parameter: τ dif = D dif − 1 K − 2 . Upon recording with mutually orthogonally polarized beams no intensity modulation occurs, but the resulting modulation of the polarization leads to the generation of light-induced linkage NO-isomers with varying efficiency according to the local state of the light polarization. This rotation of the NO ligand by nearly 90° results in a modulation of the polarizability and with this of the refractive index of the crystal.
    Journal of the Optical Society of America B 01/2010; 27(5). · 2.21 Impact Factor

Publication Stats

403 Citations
183.12 Total Impact Points

Institutions

  • 2013
    • University of Lorraine
      Nancy, Lorraine, France
  • 2005–2010
    • Universität Osnabrück
      • Institute of Chemistry
      Osnabrück, Lower Saxony, Germany
  • 1992–2010
    • University of Cologne
      • • I. Institute of Physics
      • • II. Institute of Physics
      • • Institute of Geology and Mineralogy
      • • Institute of Crystallography
      • • Thomas Institute
      Köln, North Rhine-Westphalia, Germany
  • 2009
    • Ludwig-Maximilian-University of Munich
      • Department of Biochemistry
      München, Bavaria, Germany
  • 2004
    • Universität Bern
      • Departement für Chemie und Biochemie
      Bern, BE, Switzerland
  • 2001
    • Johannes Gutenberg-Universität Mainz
      • Institute of Inorganic and Analytical Chemistry
      Mainz, Rhineland-Palatinate, Germany