Search results for "Electron transition"
showing 10 items of 58 documents
Transient Midinfrared Study of Light Induced Dissociation Reaction of Ru(dcbpy)(CO)2I2 in Solution
2004
Illumination of Ru(dcbpy)I2(CO)2 (dcbpy = 4,4‘-dicarboxy-2,2‘-bipyridine) with (near) ultraviolet light induces dissociation of one of the CO groups of the complex. In solution the opened coordination site of the metal is occupied by a solvent molecule. In the present study the kinetics of the ligand exchange reaction has been studied in solution with femtosecond time resolution by probing the CO stretching vibrations of the reactant and the product molecules Ru(dcbpy)I2(CO)(EtOH) in the infrared and probing electronic transitions in the visible spectral regions. The kinetic results indicate that photoelimination of the CO group occurs on a subpicosecond time scale. The overall quantum yiel…
Unprecedented multiple electronic spin transition in hepta- and nonanuclear complex compounds observed by Mössbauer spectroscopy
2005
Abstract The precursor [Fe(III)(5L)Cl](5LH2 = N,N′-bis(1-hydroxy-2- benzyliden)-1,7-diamino-4-azaheptane) is a high-spin (S = 5/2) complex. This precursor combined with the bridging units [Fe(II)(CN)6]4−, [Co(III)(CN)6]3−, and [Mo(CN)8]4− yields starshaped hepta- and nonanuclear clusters, [Fe(II){(CN)Fe(III)(5L)}6]Cl2, [Co(III){(CN)Fe(III)(5L)}6]Cl3 and [Mo(IV){(CN)Fe(III)(5L)}8]Cl4. The starshaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers in the Co(III)- and Mo(IV)-star switch to the low-spin state as proven by Mossbauer spectroscopy, i.e., multiple electronic transitions, while the Fe(II)-star remains in the high-spin state.
Unprecedented multistability in dodecanuclear complex compound observed by Mössbauer spectroscopy
2007
Abstract The precursors [Fe(III)( 5X L)Cl] ( 5X LH 2 = N , N ′-bis(1-hydroxy-2-benzyliden)-1,6-diamino-3-X-hexane, X = N,S) are high-spin ( S = 5/2) complexes. This precursors are combined with the bridging unit [(NC) 5 Fe(II)-CN-Co(III)(CN) 5 ] 6− to yield star-shaped dodecanuclear clusters, [( 5X LFe(III)-NC) 5 Fe(II)-CN-Co(III)(CN-Fe(III) 5X L) 5 ]Cl 4 . The star-shaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers in the N-star switch to the low-spin state as proven by Mossbauer spectroscopy, i.e. multiple electronic transitions, while the S-star remains in the high-spin state.
Tuning of the electronic and photophysical properties of ladder-type quaterphenyl by selective methylene-bridge fluorination
2016
The photophysics (spectral positions, band shapes, fluorescence quantum yields and lifetimes) of a series of fluorinated ladder type quaterphenyls L4P and L4P-Fn (n = 2, 4, 6) depend strongly on the degree and position of fluorine, despite the fact that substitution is not performed in the rings but only in methylene-bridges. This is driven by subtle differences in the molecular orbitals (MOs) participating in the electronic transitions, and in the vibronic pattern of the S0 and S1 electronic states as revealed by (TD)DFT calculations. Solid state spectra for n = 0, 2, 4 are similar to those of solution due to small intermolecular interactions as revealed by combined X-ray and (TD)DFT analy…
Laser-Calorimetric Study of Fundamental Absorption Edge in Pb,La(ZrTi)O3 (PLZT) Perovskite Ceramics
2000
The values of the light absorption coefficient of PLZT 10/65/35 ceramics at selected wavelengths have been obtained by laser calorimetric measurements. The absorption coefficient of the PLZT ceramics is an exponential function of the photon energy. Two values of characteristic Urbach energy have been found ΔE1 = 106 meV and ΔE2 = 238 meV. The first one is a characteristic of the potential of electron-phonon interaction of the optically excited transitions from the valence band to the conduction band and does not depend on lattice defects or admixtures. The other characterises the electron-phonon interaction at optical transitions between two localized electron states in the energy gap separ…
Ultrafast spectroscopic investigation on fluorescent carbon nanodots: the role of passivation.
2019
Disentangling the respective roles of the surface and core structures in the photocycle of carbon nanodots is a critical open problem in carbon nanoscience. While the need of passivating carbon dot surfaces to obtain efficiently emitting nanoparticles is very well-known in the literature, it is unclear if passivation introduces entirely new surface emitting states, or if it stabilizes existing states making them fluorescent. In this multi-technique femtosecond spectroscopy study, the relaxation dynamics of non-luminescent (non-passivated) carbon dots are directly compared with their luminescent (passivated) counterparts. Non-passivated dots are found to host emissive states, albeit very sho…
Luminescence of natural α-quartz crystal with aluminum, alkali and noble ions impurities
2019
This work was supported by the Latvian Science Council Grant No lzp-2018/1–0289 .
Electronic excitations in ZnWO4 and ZnxNi1−x WO4 (x = 0.1 − 0.9) using VUV synchrotron radiation
2011
The photoluminescence spectra and luminescence excitation spectra of pure microcrystalline and nano-sized ZnWO4 as well as the Zn x Ni1−x WO4 solid solutions were studied using vacuum ultraviolet (VUV) synchrotron radiation. The samples were also characterized by x-ray powder diffraction. We found that: (i) the shape of the photoluminescence band at 2.5 eV, being due to radiative electron transitions within the [WO6]6− anions, becomes modulated by the optical absorption of Ni2+ ions in the Zn x Ni1−x WO4 solid solutions; and (ii) no significant change in the excitation spectra of Zn0.9Ni0.1WO4 is observed compared to pure ZnWO4. At the same time, a shift of the excitonic bands to smaller en…
Luminescence of localized states in oxidized and fluorinated silica glass
2019
This work was supported by the Latvian Science Council Grant No lzp-2018/1-0289.
Protonation effects on the UV/Vis absorption spectra of imatinib: A theoretical and experimental study
2014
An experimental and theoretical investigation of protonation effects on the UV/Vis absorption spectra of imatinib showed systematic changes of absorption depending on the pH, and a new absorption band appeared below pH 2. These changes in the UV/Vis absorption spectra were interpreted using quantum chemical calculations. The geometry of various imatinib cations in the gas phase and in ethanol solution was optimized with the DFT/B3LYP method. The resultant geometries were compared to the experimentally determined crystal structures of imatinib salts. The semi-empirical ZINDO-CI method was employed to calculate the absorption lines and electronic transitions. Our study suggests that the forma…