Search results for "absorptio"
showing 10 items of 2815 documents
<title>Optical properties of hydrogen-containing MgO crystal</title>
2008
The photoluminescence (PL), its excitation (PLE) and absorption spectra in ultraviolet, visible and infrared (UV-VIS-IR) regions were used to investigate the MgO single crystals irradiated by fast neutrons. It is shown that the photoluminescence band of the MgO crystals at 730 nm belongs to the hydrogen-containing complex centers V-OH-Fe3+, which are transformed during the irradiation with fast neutrons. The behavior of the PL band 730 nm after fast neutron irradiation depends on the iron-chromium concentration. It is found that the fast neutron irradiation produces the interstitial proton H+i and the Mg(OH)2 microphase.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineer…
Photostimulated processes in the CsI-Tl crystal after UV irradiation
1997
The photostimulated luminescence is studied for CsI-Tl crystal after irradiation with ultraviolet light in the 80 - 300 K temperature range. The PSL creation spectrum coincides with the D absorption band at 80 K. Three bands are observed in the stimulation spectra at 80 K: 1400, 950, and 600 nm. The 1400 and 950 nm stimulation bands are presumably explained as optical transitions in the Tl 0 and V k centers situated in the spatial correlated pairs. The stimulation at 600 nm band is ascribed to the unperturbed Tl 0 centers.
Emission of real phonons due to electron’s self-dressing in a covalent crystal
2011
A slow monoelectronic excitation in a covalent crystal at the temperature T=0 is analyzed. The interaction with zero-point longitudinal acoustic phonons leads to the formation of a dressed electronic state at an energy level lower than that of the initial bare state. This aspect of the dressing process is described here by hypothesizing that the excess of energy is released with the emission of real phonons. Specifically, this paper considers the transition probability from the bare monoelectronic state to a dressed state of the electron accompanied by real phonons and a deformation field. The spectrum of the real phonons emitted during the electronic self-dressing is calculated by applying…
X-ray-absorption spectroscopy ofNd3+-exchanged β-alumina crystal
1996
The results of x-ray-absorption spectroscopy investigations of ${\mathrm{Nd}}^{3+}$ ions in a nearly fully exchanged (93%) sodium \ensuremath{\beta}-alumina crystal are reported. The ${\mathrm{Nd}}^{3+}$ local environment is reconstructed using a multishell best fit procedure and is compared with existing structural models. The experimental extended x-ray-absorption fine-structure (EXAFS) spectra are also compared with model ab initio FEFF6 calculations based on the x-ray-diffraction data for the ${\mathrm{Nd}}^{3+}$ ions located at the BR(2d) and interstitial A(6h) sites of \ensuremath{\beta}-alumina. Neodymium ions are mainly found near the BR(2d) sites of the conduction plane, where they…
Factors affecting the UV-Transparency of Molecular Sieves
1994
The optical properties in the UV-region of several types of molecular sieves were studied. The initial onset of absorption around 280 nm which was observed for basically all samles synthesized without special precautions is not due to an early onset of band gap absorption, but might be correlated to the crystal size as well as structural defects within the crystals, e.g. E'-center or peroxy-radical. Using template free synthesis procedures which lead to small crystals containing few defect sites, we were able to synthesize molevular sieves which were almost completely transparent down to 200 nm. Such crystals can become very important in the development of technical luminophores.
Ab initio calculations of the Ni K ‐edge XANES in Ni c Mg 1‐c O solid solutions
2005
An interpretation of the Ni K-edge X-ray absorption near edge structure (XANES) in pure NiO and NicMg1-cO solid solutions is given based on three types of ab initio theoretical calculations: the full-multiple-scattering (FMS) approach, the finite difference method (FDM) and the full potential linear muffin-tin orbital (FP-LMTO) method within the LSDA+U approach. The first two methods differ in the cluster potential approximation: the spherically symmetric muffin-tin potential is used in the FMS approach, whereas a non-muffin-tin numerical potential makes the core of the FDM. We found that the FMS and FDM techniques allow rather accurate description of the experimental XANES signal especiall…
Decoupling the artificial special pair to slow down the rate of singlet energy transfer
2012
Trimer 2, composed of a cofacial heterobismacrocycle, octamethyl-porphyrin zinc(II) and bisarylporphyrin zinc(II) held by an anthracenyl spacer, and a flanking acceptor, bisarylporphyrin free-base ( Ar = -3,5-(t Bu )2 C 6 H 3), has been studied by means of absorption spectroscopy, "steady state and time-resolved fluorescence" and fs transient absorption spectroscopy, and density functional theory (DFT) in order to assess the effect of decoupling the chromophores' low energy MOs on the rate of the singlet, S1, energy transfer, k ET , compared to a recently reported work on a heavily coupled trimeric system, Trimer 1, [biphenylenebis(n-nonyl)porphyrin zinc(II)]-bisarylporphyrin free-base ( A…
Formation of complex defects in Mn c Mg 1–c O and Ni c Mg 1–c O single solid solution
2005
The results of investigation of the fast neutron irradiation and thermal treatment on absorption spectra of single solid solution of MncMg1–cO, NicMg1–cO and MgO crystals are presented. It is shown that at impurity ion concentration larger than 0.1 mass.% a probability of formation of aggregate centers consisting of more than three F+- or F-centers is small. After thermal treatment of MncMg1–cO and NicMg1–cO single solid solution irradiated by fast neutrons additional wide bands are observed. We assume that these additional bands belong to complex centers of Mn3+-VMg and Ni3+-VMg. The mechanisms of bands formation are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Monodisperse Dialkoxy-Substituted Oligo(phenyleneethenylene)s
2006
Individual but connected synthetic routes for the preparation of the all-E-configured 2,5-dipropoxy-substituted oligo(1,4-phenyleneethenylene)s 1a–g were developed. An increasing number of conjugated stilbene units from n = 1 to n = 11 led to a convergent bathochromic shift (Δλ = λ∞ − λ1 = 127 nm) in the UV/Vis absorption. An exponential function for the convergence of the absorption energies (wavelengths) in conjugated systems is proposed. By a simple extrapolation of this function the effective chain length may be determined.
Exciton interactions in self-organised bacteriochlorophyll a - aggregates
2002
Exciton interactions of self-organised bacteriochlorophyll a - aggregates in non-polar solution linked via water and dioxane have been studied. Absorption and CD spectra of the aggregates show large red shifts typical of J-aggregates. Femtosecond excitation of the Qy band of the aggregates is followed by wavelength dependent non-exponential picosecond relaxation and anisotropy decay takes place in subpicosecond time scale. To explain these observations exciton theory and semi-empirical MO/CI calculations, that constitute the basis of the CIEM-approach developed by Linnanto et al. (J. Phys. Chem. B, 1999, 103B, 8739) was used. Structural models of aggregates were created by using the molecul…