Structure Of Excitation Spectrum Research Articles

Electronic structure and inner-shell excited luminescence in gadolinium molybdate single crystals

An electronic structure of Gd2(MoO4)3 was studied using methods of luminescence and X-ray photoelectron spectroscopy. Luminescent properties under excitation were investigated in energy ranges 125–165 and 526–553 eV which correspond to Gd4d and O1s shells. Luminescence excitation spectra were antibate to X-ray absorption spectra. The X-ray photoelectron spectroscopy appended these data by density of states in energy ranges where no resonant structures in excitation spectra were found. A low-temperature emission of Gd3+ ions was registered in gadolinium molybdate for the first time. Possible models of energy transfer in cation sublattice are discussed.

Energy spectrum analysis and finite temperature properties of the Falicov-Kimball model with Hund coupling at half filling

The Falicov-Kimball model supplemented with the Ising-type Hund coupling describes charge and magnetic order induced by on-site, charge-, and spin-dependent interactions between itinerant electrons and localized ions. Motivated by a discovery of the rich structure of ground-state phase diagrams containing various charge and magnetic superstructures, we analyze the energy spectrum and determine numerically finite temperature properties of the model on the square $4\ifmmode\times\else\texttimes\fi{}4$ cluster at half filling. For the density of magnetic ions equal to 1 and 1/2 and not too small coupling constants we show that many-electron collective excitations derived from changes in positions of the ions or inversions their spins have much lower energy than single-electron excitations. From an analysis of the excitation spectrum structure we derive effective interactions between the ions. When the coupling constants are large enough the interactions reduce to two-body forces between ions occupying the nearest-neighboring sites. Finite-temperature characteristics and temperatures of transformation from charge or magnetically ordered to disordered phases are determined in the wide range of the interaction couplings.

ChemInform Abstract: Jet Spectroscopy and Excited State Dynamics of Benzyl and Substituted Benzyl Radicals.

Benzyl and its p‐fluoro and p‐methyl derivatives are produced by the ArF laser (193 nm) photolysis of their chlorides in the supersonic free jet. The spectroscopy and excited state dynamics of these radicals are studied by the laser induced fluorescence (LIF) method under the collision free condition. The assignments of vibronic bands are carried out from the LIF excitation and dispersed spectra and the vibrational energies of the D1 state are determined. The excitation spectrum of p‐fluorobenzyl shows quite similar vibrational structure to that of p‐fluorotoluene up to about 1000 cm−1 from the 000 band, which indicates that D2 of p‐fluorobenzyl lies about 1000 cm−1 above D1 and no vibronic coupling exists lower than this energy. On the other hand, benzyl and p‐methylbenzyl show very complicated and irregular vibronic structures in excitation spectra, which are not similar to those of toluene and p‐xylene. This complication is explained by the D1–D2 vibronic coupling caused by low lying D2 states in these radicals. Time profiles of the emission intensity of p‐fluorobenzyl and p‐methylbenzyl show single exponential decay and their lifetimes do not indicate significant dependence on vibronic levels. On the other hand, benzyl shows dual exponential decay, which is interpreted by intermediate coupling case behavior.

Jet spectroscopy and excited state dynamics of benzyl and substituted benzyl radicals

Benzyl and its p-fluoro and p-methyl derivatives are produced by the ArF laser (193 nm) photolysis of their chlorides in the supersonic free jet. The spectroscopy and excited state dynamics of these radicals are studied by the laser induced fluorescence (LIF) method under the collision free condition. The assignments of vibronic bands are carried out from the LIF excitation and dispersed spectra and the vibrational energies of the D1 state are determined. The excitation spectrum of p-fluorobenzyl shows quite similar vibrational structure to that of p-fluorotoluene up to about 1000 cm−1 from the 000 band, which indicates that D2 of p-fluorobenzyl lies about 1000 cm−1 above D1 and no vibronic coupling exists lower than this energy. On the other hand, benzyl and p-methylbenzyl show very complicated and irregular vibronic structures in excitation spectra, which are not similar to those of toluene and p-xylene. This complication is explained by the D1–D2 vibronic coupling caused by low lying D2 states in these radicals. Time profiles of the emission intensity of p-fluorobenzyl and p-methylbenzyl show single exponential decay and their lifetimes do not indicate significant dependence on vibronic levels. On the other hand, benzyl shows dual exponential decay, which is interpreted by intermediate coupling case behavior.

Exciton structures in excitation spectra of impurity emission in ZnS

Exciton structures in luminescence excitation spectra of Mn, Al or Te doped hexagonal ZnS have been investigated at liquid nitrogen temperature. Mn 2+ and edge-luminescent centers are shown to bind intrinsic excitons. Al-SAL in hex. ZnS: Al is assigned as consisting of two bands due to exciton recombination at isoelectronic [Al +V 2− ZnAl +] centers and DI pair recombination.

Luminescence of Alkali Halide Phosphors Excited with XUV Radiation

Photoluminescence of alkali halide phosphors activated with Ag + or Tl + ions is studied in the XUV region from 10 eV to 40 eV. Excitation spectrum of the luminescence is found to be very rugged and two prominent peaks are observed in the photon energy region studied. The appearance of these peaks is attributed to the slowing down of the conduction electrons caused by excitation of the valence electrons. Some fine structures are also found on the gross structure of excitation spectra at the same energies with the core exciton bands.