Search results for "EXCITATION"
showing 10 items of 1290 documents
Temperature and excitation energy dependence of decay processes of luminescence in Ge-doped silica
2003
We report experimental results on the time decay of photoluminescence at 4.2 eV in Ge-doped silica. This optical emission is assigned to a singlet-singlet transition between electronic states localized on an oxygen deficiency nearby a Ge atom and its radiative decay rate is in competition with an intersystem crossing mechanism that populates an excited triplet state. We investigate the dependence of the lifetime of this photoluminescence on the temperature, in the 6--295 K range, and on the excitation energy, in the ultraviolet and vacuum ultraviolet region. The mean value of the decay time decreases on increasing the temperature, in agreement with the phonon-assisted nature of the intersys…
Luminescence and vacuum ultraviolet excitation spectroscopy of samarium doped SrB4O7
2020
Abstract Sm2+ and Sm3+ co-doped SrB4O7 could be utilized in several high-level optical devices and fundamental knowledge about the optical behavior of these materials benefits the development of luminescent applications. Herein, we report luminescence and its vacuum ultraviolet (VUV) excitation spectra in samarium doped SrB4O7. Both, Sm2+ and Sm3+ luminescence centers have been examined and distinguished in the emission and the excitation spectra investigated under synchrotron radiation. The contribution of either Sm2+ or Sm3+ emission lines into the emission spectra heavily depended on the excitation energy, and strong f-f transitions of both Sm2+ and Sm3+ were detected. At 10 K, a broad i…
UV light energy storage and thermoluminescence in AlN ceramics
2007
AlN ceramics, untreated and subjected to oxygen ion implantation, are studied for potential application in TL dosimetry of UV light. Based on photoluminescence and thermoluminescence measurements there are shown advantages of the selection of the 480 emission band for TL signal recording instead of the previously used 400 nm band: higher intensity of the TL signal, lower fading rate of the accumulated TL signal, excitation region (270-340 nm) corresponding to UV-B range, monitoring of which is actual in UV dosimetry. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Luminescence of γ-radiation-induced defects in α-quartz
2004
Optical transitions associated with γ-radiation-induced defects in crystalline α-quartz were investigated by photoluminescence excited by both pulsed synchrotron radiation and steady-state light. After a 10 MGy γ-dose we observed two emissions at 4.9 eV (ultraviolet band) and 2.7 eV (blue band) excitable in the range of the induced absorption band at 7.6 eV. These two luminescence bands show a different temperature dependence: the ultraviolet band becomes bright below 80 K; the blue band increases below 180 K, but drops down below 80 K. Both emissions decay in a timescale of a few ns under pulsed excitation, however the blue band could also be observed in slow recombination processes and it…
A rotating wheel system for the detection of spontaneously fissioning nuclides from heavy ion reactions
1981
Abstract A rotating wheel system for the detection of spontaneously fissioning reaction products from heavy ion reactions was developed. In this system products recoiling from a rotating target wheel are stopped in a catcher foil stack which can be rotated at various velocities up to 80 rotations per second. All products emitted within a wide emission cone are stopped in the catcher foils and are rotated into shielded positions with stationary fission-track detectors positioned on both sides of each rotating foil. This technique allows a sensitive detection of spontaneously fissioning nuclides over a broad range of half-lives from 1 ms to about 1 d. By post-bombardment exposure of the catch…
Luminescence of ZnO nanopowders
2004
Abstract The luminescence of ZnO nanocrystals prepared by different methods was studied under pulsed electron beam excitation. It is shown that the luminescence intensity depends on the nanocrystal sintering conditions and does not depend on the nanocrystal size within the range 10–50 nm. The relative luminescence intensities for the 3.32 eV (free exciton) and ∼3.20 eV (bound exciton) bands showed a dependence on nanocrystal size. The role of the nanocrystal surface in excitonic luminescence is discussed.
The influence of internal degrees of freedom on the unimolecular decay of the molecule–cluster compound Au8+CH3OH
2002
Time-resolved photodissociation measurements of the sequential reaction Au8+CH3OH→Au8+→Au7+ and the direct reaction Au8+→Au7+ have been performed for several excitation energies. The production rates and yields of the final state Au7+ in the sequential process are strongly influenced by the excitation energy deposited into the evaporated methanol molecule during the initial fragmentation step. Both the rate constants and yields can be fitted with a single parameter, the cluster–methanol binding energy.
Lineshapes and optical selectivity in high-resolution double-resonance ionization mass spectrometry
1999
Abstract Lineshapes expected in high-resolution double-resonance ionization spectroscopy are calculated using the density matrix formalism, integrated over experimentally realistic conditions including atomic velocity and angular distributions as well as laser intensity profiles. The results of these calculations are compared with experimental measurements on the system 4s2 1S0 → 4s4p 1P1 → 4s4d 1D1 → ion for calcium. The measurements of lineshape, with a dynamic range of >106, reveal and confirm subtle effects predicted by theory. These include the shape, position and intensity of the laser-induced structure in the spectra and the simultaneous presence of coherent and incoherent excitation…
Computational determination of the dominant triplet population mechanism in photoexcited benzophenone
2014
In benzophenone, intersystem crossing occurs efficiently between the S-1(n pi(star)) state and the T-1 state of dominant n pi(star) character, leading to excited triplet states after photoexcitation. The transition mechanism between S-1(n pi(star)) and T-1 is still a matter of debate, despite several experimental studies. Quantum mechanical calculations have been performed in order to assess the relative efficiencies of previously proposed mechanisms, in particular, the direct S-1 -> T-1 and indirect S-1 -> T-2(pi pi(star)) -> T-1 ones. Multiconfigurational wave function based methods are used to discuss the nature of the relevant states and also to determine minimum energy paths a…
Time-dependent ground-state correlations in heavy ion scattering
1982
Using a time-dependent generator-coordinate method, we derive a theory for time-dependent collective ground-state correlations which account for some quantum fluctuations about a TDHF trajectory. This theory is particularly suited for evaluating spreading widths of collective one-body operators. As an application we study head-on collision of heavy ions in a one-dimensional model. As one of the prominent results we find a substantial enhancement of the spreading width of the internal excitation energy due to the correlations.