Search results for "Excited state"
showing 10 items of 1387 documents
Large scale modelling of photo-excitation processes in materials with application in organic photovoltaics
2019
La energía fotovoltaica a partir de materiales orgánicos representa una opción muy atractiva, en términos de costo y flexibilidad, para generar electricidad. Sin embargo, las bajas eficiencias alcanzadas hasta ahora limitan la producción de dispositivos fotovoltaicos a escala comercial. En el intento de superar las bajas eficiencias hoy en día se dedican considerables esfuerzos en la investigación y el diseño de materiales orgánicos así como de arquitecturas de dispositivos más eficientes. En particular esta tesis doctoral presenta un trabajo de carácter fundamental sobre los procesos de fotoexcitación en dispositivos optoelectrónicos orgánicos, donde se usan química teórica y modelización …
Fast Photochemistry of Prototypical Phytochromes : A Species vs. Subunit Specific Comparison
2015
Phytochromes are multi-domain red light photosensor proteins, which convert red light photons to biological activity utilizing the multitude of structural and chemical reactions. The steady increase in structural information obtained from various bacteriophytochromes has increased understanding about the functional mechanism of the photochemical processes of the phytochromes. Furthermore, a number of spectroscopic studies have revealed kinetic information about the light-induced reactions. The spectroscopic changes are, however, challenging to connect with the structural changes of the chromophore and the protein environment, as the excited state properties of the chromophores are very sens…
Multiparticle configurations of excited states in 155Lu
2016
Excited states in the neutron-deficient N=84 nuclide 155Lu have been populated by using the 102Pd(58Ni,αp) reaction. The 155Lu nuclei were separated by using the gas-filled recoil ion transport unit (RITU) separator and implanted into the Si detectors of the gamma recoil electron alpha tagging (GREAT) spectrometer. Prompt γ-ray emissions measured at the target position using the JUROGAM Ge detector array were assigned to 155Lu through correlations with α decays measured in GREAT. Structures feeding the (11/2−) and (25/2−)α-decaying states have been revised and extended. Shell-model calculations have been performed and are found to reproduce the excitation energies of several of the low-lyin…
Bright Visible Luminescence in Silica Nanoparticles
2011
International audience; We demonstrate that a porous film of silica nanoparticles emits a bright visible luminescence associated with defects stabilized by oxygen chemisorption at oxygen deficient center sites. Time-resolved spectra excited by a tunable laser allow us to distinguish the luminescence at 1.99 eV, characteristic of the nonbridging oxygen hole center (NBOHC) (Si-O)3 Si-O*, and a fast and a slow emission: the first (lifetime τ ≈ 25 ns) is peaked at 2.27 eV with an excitation spectrum centered at 5.5 eV; the second (τ ≈ 7.5 μs) is peaked at 2.41 eV and is excited around 3.2 and 5.2 eV. Reaction in an air atmosphere leads to the disappearance of the NBOHC luminescence and of the …
Search for the double-beta decay of 82Se to the excited states of 82Kr with NEMO-3
2020
The double-beta decay of 82Se to the 0+1 excited state of 82Kr has been studied with the NEMO-3 detector using 0.93 kg of enriched 82Se measured for 4.75 y, corresponding to an exposure of 4.42 kg y. A dedicated analysis to reconstruct the gamma-rays has been performed to search for events in the 2e2g channel. No evidence of a 2nbb decay to the 0+1 state has been observed and a limit of T2n 1/2(82Se; 0+gs -> 0+1) > 1.3 1021 y at 90% CL has been set. Concerning the 0nbb decay to the 0+1 state, a limit for this decay has been obtained with T0n 1/2(82Se; 0+g s -> 0+1) > 2.3 1022 y at 90% CL, independently from the 2nbb decay process. These results are obtained for the first time with a tracko-…
High-sensitivity study of levels in 30Al following β decay of 30Mg
2016
γ -ray and fast-timing spectroscopy were used to study levels in 30Al populated following the β− decay of 30Mg. Five new transitions and three new levels were located in 30Al. A search was made to identify the third 1+ state expected at an excitation energy of ∼2.5 MeV. Two new levels were found, at 3163.9 and 3362.5 keV, that are firm candidates for this state. Using the advanced time-delayed (ATD) βγγ (t) method we have measured the lifetime of the 243.8-keV state to be T1/2 = 15(4) ps, which implies that the 243.8-keV transition is mainly of M1 character. Its fast B(M1; 2+ → 3+) value of 0.10(3) W.u. is in very good agreement with the USD shell-model prediction of 0.090 W.u. The 1801.5-k…
Quantum Motion of Chemisorbed Hydrogen on Ni Surfaces
1983
Quantum mechanical energy levels and wave functions have been calculated for the motion of chemisorbed hydrogen atoms on Ni surfaces. The results show considerable quantum effects for the adatom in both the ground and the excited states. The description of the adparticles as being delocalized along the surface offers a novel interpretation of several phenomena, in particular the vibrational excitations. Peer reviewed
Photoluminescence time decay of surface oxygen deficient centers in un‐doped and Ge‐doped silica
2005
We report a study of the emission decay from the singlet excited state of two fold coordinated Si and Ge centers stabilized on the surface of silica and Ge-doped silica. The PL lifetimes are of the order of nanoseconds and increase on decreasing the temperature. The results suggest that, for the surface centers, the phonon assisted intersystem-crossing process linking the excited states affects the decay rates, is effective down to low temperatures and is distributed because of the inhomogeneity of the defects. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Protonation of the Biliverdin IXα Chromophore in the Red and Far-Red Photoactive States of Bacteriophytochrome
2019
The tetrapyrrole chromophore biliverdin IXα (BV) in the bacteriophytochrome from Deinococcus radiodurans (DrBphP) is usually assumed to be fully protonated, but this assumption has not been systematically validated by experiments or extensive computations. Here, we use force field molecular dynamics simulations and quantum mechanics/molecular mechanics calculations with density functional theory and XMCQDPT2 methods to investigate the effect of the five most probable protonation forms of BV on structural stability, binding pocket interactions, and absorption spectra in the two photochromic states of DrBphP. While agreement with X-ray structural data and measured UV/vis spectra suggest that …
VUV emission spectroscopy combined with H- density measurements in the ion source Prometheus I
2016
“Prometheus I” is a volume H− negative ion source, driven by a network of dipolar electron cyclotron resonance (ECR; 2.45 GHz) modules. The vacuum-ultraviolet (VUV) emission spectrum of low-temperature hydrogen plasmas may be related to molecular and atomic processes involved directly or indirectly in the production of negative ions. In this work, VUV spectroscopy has been performed in the above source, Prometheus I, both in the ECR zones and the bulk (far from ECR zones and surfaces) plasma. The acquired VUV spectra are correlated with the negative ion densities, as measured by means of laser photodetachment, and the possible mechanisms of negative ion production are considered. The well-e…