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Emission Energy (emission + energy)
Selected AbstractsTetranuclear (Phosphane)(thiolato)gold(I) Complexes: Synthesis, Characterization and Photoluminescent Properties,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2007Eduardo J. Fernández Abstract The reactions of the tetraphosphane donor ligand (Ph2PCH2)2NCH2CH2N(CH2PPh2)2 with the gold precursors [AuCl(tht)] or [Au(C6F5)(tht)] (tht = tetrahydrothiophene) leads to complexes [Au4R4{(Ph2PCH2)2NCH2CH2N(CH2PPh2)2}] [R = Cl (1) or C6F5 (2)]. Further substitution of the chlorine atoms in 1 by the corresponding 4-substituted benzenethiolates gives rise to the tetranuclear (phosphane)(thiolato)gold(I) complexes [Au4(S-C6H4 -X)4{(Ph2PCH2)2NCH2CH2N(CH2PPh2)2}] [X = F (3), MeO (4), Me (5) and NO2 (6)]. Complexes 2 and 4 were characterized by X-ray diffraction studies showing Au···Au interactions in the case of complex 4. Complexes 3,6 display intense emissions in the solid state at 77 K with lifetimes in the microsecond range. The observed phosphorescent emissions are attributed to metal-to-ligand charge-transfer transitions. Nevertheless, the influence in the emission energies of gold,gold interactions or the contribution of the substituent in the 4-position of the benzenethiolate ring to the excited state cannot be neglected. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1,5)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Jinglai Zhang Abstract The density functional theory (DFT) and the complete active space self-consistent-field (CASSCF) method have been used for full geometry optimization of carbon chains C2nH+ (n = 1,5) in their ground states and selected excited states, respectively. Calculations show that C2nH+ (n = 1,5) have stable linear structures with the ground state of X3, for C2H+ or X3,, for other species. The excited-state properties of C2nH+ have been investigated by the multiconfigurational second-order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low-lying states in C2nH+ (n = 1,5). Present results indicate that the predicted vertical excitation and emission energies of C2nH+ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Hydrogenation of strain engineered InAs/InxGa1,x As quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2004D. Ochoa Abstract InxGa1,xAs/InAs/InxGa1,xAs structures have been grown by atomic layer molecular beam epitaxy on top of a GaAs buffer and substrate. In these structures, the thickness d and/or the In composition x of the lower InxGa1,xAs confining layer control the strain in self-assembled quantum dots. This strain engineering has allowed achieving emission energies as low as 1.5 ,m at low T, with a rapid quenching of the photoluminescence (PL) signal at high T. Hydrogen irradiation of these structures leads to an increase in the PL efficiency, higher in samples with higher x, with a blue shift in the peak energy. A higher concentration of non radiative defects in confining layers richer in indium is responsible for the observed PL quenching, more than an increased thermal escape of carriers toward the InxGa1,xAs barriers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Degradation of Structural and Optical Properties of InGaN/GaN Multiple Quantum Wells with Increasing Number of WellsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003S. Pereira Abstract We compare the structural and spectral properties of two multi quantum wells (MQWs), grown by metal organic chemical vapour deposition under the same nominal conditions, with a different number of periods. The MQWs, each with 20% InN and containing 8 and 18 wells, respectively, grew on-axis and coherent to GaN, as revealed by X-ray diffraction reciprocal space mapping (RSM) analysis. Comparison of the asymmetrical (105) RSMs indicates an overall structural deterioration and greater well-barrier intermixing for the MQW with the larger number of wells. Moreover, the composition of the MQWs was depth-profiled by grazing incidence Rutherford backscattering spectrometry (RBS). RBS further evidences strong intermixing in the 18-well heterostructure. The deleterious effects of intermixing on the emission spectrum are revealed by low temperature photoluminescence spectroscopy. Despite similar peak emission energies (,E < 45 meV) the 8-well structure shows a more symmetric and narrow peak (FWHM , 100 meV) in comparison with that of the 18-well sample (FWHM , 170 meV). Surface analyses by atomic force and scanning electron microscopy show an increased density, size and depth of V-pit defects on the 18-well structure. These results suggest that dislocations and pitting result from a larger elastic strain energy accumulated in the thicker MQW stack and are a fundamental intermixing mechanism for InGaN/GaN MQWs. [source] Positively Charged Iridium(III) Triazole Derivatives as Blue Emitters for Light-Emitting Electrochemical CellsADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Mathias Mydlak Abstract Cationic blue-emitting complexes with (2,4-difluoro)phenylpyridine and different 1,2,3-triazole ligands are synthesized with different counterions. The influence of the substituents on the triazole ligand is investigated as well as the influence of the counterions. The substituents do not change the emission energy but, in some cases, slightly modify the excited-state lifetimes and the emission quantum yields. The excited-state lifetimes, in apolar solvents, are slightly dependent on the nature of the counterion. A crystal structure of one of the compounds confirms the geometry and symmetry postulated on the basis of the other spectroscopic data. Light-emitting electrochemical cell devices are prepared and the recorded emission is the bluest with the fastest response time ever reported for iridium complexes. [source] Theoretical studies on structures and electronic spectra of linear carbon chains C2nH+ (n = 1,5)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2009Jinglai Zhang Abstract The density functional theory (DFT) and the complete active space self-consistent-field (CASSCF) method have been used for full geometry optimization of carbon chains C2nH+ (n = 1,5) in their ground states and selected excited states, respectively. Calculations show that C2nH+ (n = 1,5) have stable linear structures with the ground state of X3, for C2H+ or X3,, for other species. The excited-state properties of C2nH+ have been investigated by the multiconfigurational second-order perturbation theory (CASPT2), and predicted vertical excitation energies show good agreement with the available experimental values. On the basis of our calculations, the unsolved observed bands in previous experiments have been interpreted. CASSCF/CASPT2 calculations also have been used to explore the vertical emission energy of selected low-lying states in C2nH+ (n = 1,5). Present results indicate that the predicted vertical excitation and emission energies of C2nH+ have similar size dependences, and they gradually decrease as the chain size increases. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Effects of Si doping position on the emission energy and recombination dynamics of GaN/AlGaN multiple quantum wellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2006Hamid Haratizadeh Abstract We report results from detailed optical spectroscopy from MOCVD grown GaN/Al0.07Ga0.93N multiple quantum wells (MQWs). Effects of Si doping position on the emission energy and recombination dynamics were studied by means of photoluminescence (PL) and time-resolved PL measurements. The samples were Si doped with the same level but different position of the dopant layer. Only the sample doped in the well shows the MQW emission redshifted compare to the GaN bandgap. The redshift is attributed to the self-energy shift of the electron states due to the correlated motion of the electrons exposed to the fluctuating potential of the donor ions. At low temperature the PL decay time of the sample doped in the well by a factor of two is longer than for the barrier doped case. The difference is explained by the effect of interplay of free carriers and ions on the screening of the polarization field in these doped structures. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Dependence of the band-gap pressure coefficients of self-assembled InAs/GaAs quantum dots on the quantum dot sizePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007C. Kristukat Abstract We report on low-temperature photoluminescence experiments on self-assembled InAs/GaAs quantum dots under high hydrostatic pressure up to 8 GPa using a diamond anvil cell. The sample exhibits a multimodal size distribution of the quantum dots, which gives rise to a characteristic emission profile displaying up to nine clearly separable peaks attributed to the ground-state recombination from each quantum dot subensemble with different size. Structural analysis revealed that their size differs in entire monolayer steps. The measured pressure coefficients for each subensemble show a linear dependence on their zero-pressure emission energy ranging from 65 meV/GPa for the largest dots to 112 meV/GPa for the smallest ones. Pressure dependent strain simulations based on an atomistic valence-force field yield that the pressure coefficient of the InAs band-gap is strongly reduced when InAs is embedded in a GaAs matrix. Taking into account confinement effects within the envelope function approximation, the calculated pressure coefficients are in good agreement with the experimental findings. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exciton localization in MgxZnyCd1,x,ySe alloyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004O. Maksimov Abstract We report photoluminescence and reflectivity measurements of MgxZnyCd1,x,ySe epitaxial layers (0 < x < 0.53) grown by molecular beam epitaxy on InP (100) substrates. Significant emission line broadening, increase in activation energy and Stokes shift are monitored with increasing Mg content. For MgxCdyZn1,x,ySe samples with large Mg content (x > 0.3), we observe an anomalous temperature dependence of both the emission energy and line broadening. This behavior is assigned to the emission from localized states. Different mechanisms of carrier localization are discussed and exciton localization on statistical CdSe clusters is proposed to be the most likely one. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structures and Solvatochromic Phosphorescence of Dicationic Terpyridyl,Platinum(II) Complexes with Foldable Oligo(ortho -phenyleneethynylene) Bridging LigandsCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2008Ming-Xin Zhu Abstract A series of binuclear organoplatinum(II) complexes, [(tBu3tpy)Pt(CC1,2-C6H4)nCCPt(tBu3tpy)][ClO4]2 (1,7, n=1, 2, 3, 4, 5, 6, 8; tBu3tpy=4,4,,4,,-tri- tert -butyl-2,2,:6,,2,,-terpyridine) with foldable oligo(ortho -phenyleneethynylene) linkers were prepared and characterized by spectroscopic methods and/or X-ray crystallographic analyses. In the crystal structures of 3,2.5,CH3OH, 5,CH3CN, and 6,4,CH3CN, each of the bridging ortho -phenyleneethynylene ligands has a partially folded conformation. In aerated water/acetonitrile mixtures with water percentages larger than 40,%, the emission of complexes 3,7 are red-shifted and enhanced when compared to those recorded in acetonitrile. The red-shift in emission energy and enhanced emission intensity can be attributed to the inter- and/or intramolecular interactions induced by the addition of water to solutions of the platinum(II) complexes in acetonitrile. Data from dynamic light scattering and transmission electron microscopy studies revealed that these binuclear platinum(II) complexes aggregated into nanosized particles in acetonitrile/water mixtures. Hydrophobic folding of the ortho -phenyleneethynylene linkers in acetonitrile/water mixtures is postulated. [source] Fluorophores as Optical Sensors for Local Forces,CHEMPHYSCHEM, Issue 12 2009Stefan Marawske Abstract The main aim of this study is to investigate correlations between the impact of an external mechanical force on the molecular framework of fluorophores and the resultant changes in their fluorescence properties. Taking into account previous theoretical studies, we designed a suitable custom-tailored oligoparaphenylenevinylene derivative (OPV5) with a twisted molecular backbone. Thin foils made of PVC doped with 100 nM OPV were prepared. By applying uniaxial force, the foils were stretched and three major optical effects were observed simultaneously. First, the fluorescence anisotropy increased, which indicates a reorientation of the fluorophores within the matrix. Second, the fluorescence lifetime decreased by approximately 2.5,% (25 ps). Finally, we observed an increase in the emission energy of about 0.2,% (corresponding to a blue-shift of 1.2 nm). In addition, analogous measurements with Rhodamine 123 as an inert reference dye showed only minor effects, which can be attributed to matrix effects due to refractive index changes. To relate the observed spectroscopic changes to the underlying changes in molecular properties, quantum-chemical calculations were also performed. Semiempirical methods had to be used because of the size of the OPV5 chromophore. Two conformers of OPV5 (C2 and Cisymmetry) were considered and both gave very similar results. Both the observed blue-shift of fluorescence and the reduced lifetime of OPV5 under tensile stress are consistent with the results of the semiempirical calculations. Our study proves the feasibility of fluorescence-based local force probes for polymers under tension. Improved optical sensors of this type should in principle be able to monitor local mechanical stress in transparent samples down to the single-molecule level, which harbors promising applications in polymer science and nanotechnology. [source] Paradoxical Solvent Effects on the Absorption and Emission Spectra of Amino-Substituted Perylene Monoimides,CHEMPHYSCHEM, Issue 8 2005Peter D. Zoon Abstract In N -(2,5-di- tert -butylphenyl)-9-pyrrolidinoperylene-3,4-dicarboximide (5PI) the absorption and emission spectra display large solvatochromic shifts, but, remarkably, the Stokes shift is practically independent of solvent polarity. This unique behavior is caused by the extraordinarily large ground-state dipole moment of 5PI, which further increases upon increasing the solvent polarity, whereas the excited-state dipole moment is less solvent dependent. In the corresponding piperidine compound, 6PI, this effect is much less important owing to the weaker coupling between the amino group and the aromatic imide moiety, and in the corresponding naphthalimide, 5NI, it is absent. The latter shows the conventional solvatochromic behavior of a push,pull substituted conjugated system, that is, minor shifts in absorption and a larger change in the emission energy with solvent polarity. [source] | |||||||||||||