Electronic Vibrational Structure Research Articles

Проявление локальных колебаний в спектрах фотолюминесценции ZnO : Fe-=SUP=-3+-=/SUP=-

In this paper photoluminescense spectra and EPR-signals of ZnO single crystals, doped with manganese and containing (from EPR data) uncontrolled impurity of iron, were investigated. At the temperature of 4.5 K in photoluminescense spectrum the band in energy interval of 1.55-1.8 eV (12493 – 14508 cm-1) was observed. This band contains some intensive lines; these lines are caused by Fe3+ ions (d5-configuration). The first and most intensive line at the energy of 1.79 eV corresponds to irradiative transition 4T1 (G) → 6A1 (S) in Fe3+ ions. The other peaks are electronic-vibrational structure. This structure may be caused by force interaction in deformed Fe3+ - 4O2- - cluster.

EPR and optical spectroscopy of the Tm2+ ion in the KMgF3 single crystal

Paramagnetic Tm2+ ion centers in the KMgF3 single crystal have been studied by electron paramagnetic resonance and optical spectroscopy. The Stark level energies of the cubic Tm2+ multiplets have been established from the luminescence spectra and the crystal field parameters have been calculated. Information about the phonon spectra of KMgF3 crystals has been obtained from the electron-vibrational structure of the optical luminescence spectra.

Optical spectroscopy of Yb 3+ in the Cs 2NaYF 6 single crystal

Results of the optical spectroscopy investigation of the cubic paramagnetic center Yb 3+ ion in the Cs 2NaYF 6 single crystal are presented. The Stark level energies of the Yb 3+ multiplets are established from absorption, luminescence and excitation luminescence spectra and the crystal field parameters are calculated. Information about the phonon spectra of Cs 2NaYF 6 crystals is obtained from the electron-vibrational structure of the optical absorption and luminescence spectra.

EPR and optical spectroscopy of Yb3+ ions in CaF2: an analysis of the structure of tetragonal centers

CaF2 crystals doped with Yb3+ ions have been studied by electron paramagnetic resonance (EPR) and optical spectroscopy. EPR spectra of paramagnetic centers (PCs) for cubic (Tc) and tetragonal (Ttet) symmetries were identified. Empirical energy level diagrams were established and crystal field parameters were determined. Information on the CaF2∶Yb3+ phonon spectra was obtained from the electron-vibrational structure of the optical spectra. The crystal field parameters were used to analyze the crystal lattice distortions in the vicinity of the Yb3+ ion. Within the framework of a superposition model, it is established that four F− ions located symmetrically with respect to the fourfold axis from the side of the ion-compensator approach the impurity ion and deviate from the PC axis. The second set of four fluorine ions also approaches the Yb3+ ion and the PC axis. The ion-compensator F− also approaches considerably the impurity ion.

Electron-Vibrational Structure in the 2.8–3.6 eV Range of the Photoluminescence Spectrum of Borozon

The electron-vibrational structure in the 2.8–3.6 eV range of the photoluminescence spectrum of borozon polycrystals and single crystals has been investigated. The existence of the structure of the leading PF-1 line, its change depending on the measurement temperature and the quality of the sample and after irradiation at low temperature and annealing, and the electron-phonon interaction on the PF center with the participation of longitudinal optical phonons made it possible to develop a model of donor-acceptor recombination for interpreting the nature of the PF center.

Electron paramagnetic resonance and optical spectroscopy of Yb3+ ions inSrF2 andBaF2;an analysis of distortions of the crystal lattice near Yb3+

SrF2 and BaF2 crystals, dopedwith the Yb3+ions, have been investigated by electron paramagnetic resonanceand optical spectroscopy. As-grown crystals of SrF2 andBaF2show the two paramagnetic centres for the cubic (Tc) and trigonal (T4) symmetries ofthe Yb3+ions. Empirical diagrams of the energy levels were established and the potentialsof the crystal field were determined. Information was obtained on the SrF2 andBaF2phonon spectra from the electron-vibrational structure of the opticalspectra. The crystal field parameters were used to analyse the crystallattice distortions in the vicinity of the impurity ion and the F−ion compensating for the excess positive charge in T4.Within the frames of a superposition model, it is shown that three F− ionsfrom the nearest surrounding cube, located symmetrically with respect to the C3axis from the side of the ion-compensator, approach the impurityion and cling to the axis of the centre when forming T4. TheF−ion located on the axis of the centre between the Yb3+ion and ion-compensator, also approaches close to the impurity ion.

EPR and optical spectroscopy of the Yb3+ cubic center in β-PbF2

Optical spectroscopy and EPR are employed to study a β-PbF2 crystal doped with Yb3+ ions. The presence of only one paramagnetic center, the Yb3+ ion with cubic symmetry, is established. Its optical lines are identified, the empirical system of energy levels is constructed, and the phenomenological crystal field potential is determined. The information on the phonon spectrum of the β-PbF2 crystal is obtained from the electron-vibrational structure of the optical absorption and luminescence spectra.

The Effect of cis-trans Isomerism on the Electronic-vibrational Structure of the Ground and Excited States and Reactivity of 2-(2-Furyl)- and 2-(2-Thienyl)oxazole

The fluorescent properties, structure, and electronic structure of the ground and excited singlet and triplet electronic states of the cis and trans forms of 4,5-dihydro-2-(2-furyl)oxazole, 4,4-dihydro-2-(2-thienyl)oxazole, 2-(2-furyl)oxazole (FO), and 2-(2-thienyl)oxazole (TO) have been studied. The orbital nature of the lower excited singlet and triplet states has been studied by the semiempirical INDO/S (valence approximation) and PPP/S (π approximation) methods. It was shown that for FO and TO molecules the lower triplet state is of the ππ* type, for which delocalization of the electronic excitation on atoms is characteristic. In the singlet excitation state inversion was observed of the energy levels of the delocalized ππ* states and nπ* states localized over several bonds (for the free TO and FO molecules the lower excited singlet states S1* were assigned to ππ* and nπ* types respectively). Owing to the low position of the Tππ* and Tnπ* levels relative to the singlet level of ππ* type, the rate constant for intercombination conversion is greater than the rate constant for radiative decay. Consequently an efficient population of the triplet states of the molecules occurs under conditions of electronic-vibrational excitation. The direction of reactions during synthesis was compared with the localization indices in the ground state for electrophilic, nucleophilic, and radical substitution, and also with the excitation localization numbers Lμ for a wide selection of electronically excited states. It was concluded that the change in the structure of the azole molecule on replacing an O atom by an S atom, or on changing from a partially hydrogenated to a heteroaromatic system, was the main reason for the change of all the spectral parameters characterizing the electronic-vibrational or the spin-orbital interaction of the most reactive groups of atoms in the molecular structure.

Electronic and electronic-vibrational phenomena in the new organic conductor ϰ-(ET)2[Hg(SCN)2Cl] with a metal-insulator transition

The reflection spectra and optical conductivity spectra of the new organic conductor ϰ-(ET)2[Hg(SCN)2Cl] with a metal-insulator transition in the spectral regions 700–5500 and 9000–40 000 cm−1 have been studied in polarized light at 300 K. A comparisonis made between the spectra obtained and the corresponding spectra of related isostructural conductors based on the ET molecule, and also the properties of the crystal structure of the investigated compounds. An electronic transition between the ET molecules of the dimer (ET)2+ in the spectral region 700–5500 cm−1 has been identified, as have the features of the electronic-vibrational structure arising as a consequence of the interaction of this transition with the completely symmetric intramolecular vibrations of the ET molecule. It is found that the conductor with the stronger dimer interaction between the ET molecules has the higher the transition temperature.

Electron-vibrational structure in the 2.8?3.6 eV range of the cathodoluminescence spectra of sphaleritic boron nitride

Electron-vibrational structure in the 2.8?3.6 eV range of the cathodoluminescence spectra of sphaleritic boron nitride

The electron-vibrational structure of the 420 nm absorption band of uranyl nitrate

The present paper deals with the 420 nm absorption band of hexahydrate of uranyl nitrate UO2(NO3)2.6 H2O. The probability of absorption in this sample is calculated and compared with experiment.