A. Kikas

MONTE CARLO SIMULATION OF THE CROSSLUMINESCENCE EXCITATION SPECTRUM IN A CSBR CRYSTAL

Abstract It is shown that to understand the essential features of the crossluminescence excitation spectrum of CsBr it is necessary to suppose for holes in the uppermost cation band the validity of the inequality τ r 》 τ p > τ a , τ r being the time of their radiative relaxation (i.e. the crossluminescence decay time), τp, the time of their relaxation by scattering on phonons, and τa, the time of their interatomic Auger relaxation, and the strong influence on τp and τa of the spin-orbit splitting of the valence and the cation bands.

Autoionization phenomena involving the 2p53d configuration of argon-like ions in ionic solids

Abstract The photon-induced Auger and photoelectron spectra of the argon-like ions Cl − (in NaCl), K + (in KCl), and Ca 2+ (in CaCl 2 ) have been measured in the vicinity of the L 23 absorption edges of these ions. It is shown that at the 2p 6 → 2p 5 3d(4s) resonance, strong spectator and, in the cases of metal ions, participator effects appear in the electron spectra. The spectator structure is situated in the region of the L 23 M 23 M 23 Auger spectra and shifts to higher kinetic energies with increasing photon energy. It originates from the 3p −2 3d(4s) final configuration and arises as a product of the Auger-resonant inelastic scattering process of the incident photons. In the region of the L 2 resonances the process includes the L 2 L 3 M 45 Coster-Kronig transitions. The participator role of the excited 3d electron manifests itself as the resonant enhancement of the 3p and 3s photoelectron lines. The threshold energy for excitation of 2p electrons to the conduction band is about 202.5 eV for Cl in NaCl and 296.5 eV for K in KCl.

MNN resonant Auger spectra of Ce in CeCl3

Abstract The 3d-edge resonant electron emission spectra of Ce in CeCl 3 are measured by using synchrotron radiation. The resonant M 45 N 45 N 45 Auger spectra (3d RAES) are analysed in terms of the intraionic 3d 9 4f 2 → 4d 8 4f 2 transitions; the possible contributions from the 4d 8 4f 3 final states are discussed.

Secondary photoelectron spectra of NaCl and KBr excited by XUV radiation: Experiments and computer simulations

Energy distributions of slow electrons (0 to 10eV) emitted by thin layers of NaCl and KBr irradiated by monochromatic XUV photons with various energies in the interval of 50 to 300 eV are measured. For all cases the photoelectron spectrum starts with an intense peak of slow secondaries and has a hot-secondary structure at the energies 1 to 5 eV. The smaller the photon absorption depth, the stronger is this structure. An attempt is made to reproduce such a behaviour of spectra by a Monte Carlo simulation of electron-electron and electron-phonon scattering sequences induced in solids by XUV photon absorption. It appears that for high-energy ( > 2 to 3 eV) conduction electrons the electron-phonon scattering is mainly due to acoustic phonons.

Auger and photoelectron spectra of K+ in solids at resonant 2p6 to 2p53d excitation

Abstract We present here the 2 p -3 d -resonant photoelectron and Auger spectra of K + in KMnF 3 and compare them with analogous spectra of KCl. The spectra are very similar for both compounds. The most conspicious structure which arises during the LMM Auger spectator decay of the 2 p 5 3 d configuration is due to the 3 p −2 3 d final configuration. Its remarkable property, the linear dispersion in the whole resonance region, demonstrates that i) the Auger transition is so fast that at resonant excitation it is not possible separate it from the photon absorption process, ii) the L 2 L 3 M 45 Coster-Kronig transition is an important link in the nonradiative decay of the resonantly-created L 2 hole, and iii) the crystal-field splitting of the intermediate 2 p 5 3 d configuration does not determine the general mechanism of nonradiative decay of this configuration.

Appearance of crystal-field splitting in 2p-resonant electron spectra of K+ in ionic solids

Abstract It is known that a well-developed spectator structure appears in the electron spectra of ionic potassium compounds when excited with photons at the K+ 2p absorption region (295 – 310 eV). This structure is due to the Auger-resonant inelastic scattering process 2p6 + hv → (2p53d) → 3p43d + e, in which the 2p-hole states (the absorption final states) serve as the intermediate states. Due to the circumstance that all the configurations which contain the 3d orbitals are subject to a crystal-field splitting in solids, an interesting interplay of different bands of the electron spectra may be observed if the photon energy resonates with different crystal-field components of the absorption spectrum. Experimentally some of the crystal-filed effects are known from the comparison with each others the different spectra of KCl (here the crystal-field splitting D is about 0.9 eV) and with KMnF3 ( D ∼ 0.06 eV). We have performed theoretical calculations in which the crystal-field effects are inserted into the usual atomic Hartree-Fock procedure. The calculations reproduce well the high-kinetic-energy parts of the electron spectra.

Auger Spectra of K + L 23 Excitations in Potassium Halides

The L23M23M23 Auger spectra of K+ L23 excitation in potassium halides are measured using photon excitation with different energies in the region of the K+ L23 absorption edge (around 300 eV). It is shown that the screening of the 3p holes caused by the collapsed 3d electron of the K+ L23 exciton leads to a considerable shift (by about (6÷7) eV) of the K+ L23M23M23 Auger bands to higher energies. Only the low-energy component of the crystal-field-split K+ 3d orbital forms a genuine bound state with 2p holes, whereas its high-energy component lies in the conduction band continuum and behaves like a shape resonance.

NEXAFS of ionic solids as seen through resonant electron spectra

Abstract We show that the nonradiative decay patterns of core-hole-electron bound states (core excitons) in the regions of K L23 edge of KMnF3 and KCl, Cl L23 edge of NaCl, and F K edge of alkali fluorides include specific spectator structures which are clearly distinguishable from the normal Auger spectra excited in the regions of continuum transitions.

3d-resonant photo- and Auger emission of Ce in CeO2

The Ce 3d-edge resonant photoelectron and Auger electron emission spectra in CeO2 have been measured. The 4s-, 4p- and 4d-emission at off-resonance excitations consists of two parts separated by ab ...

L23MM resonnant auger spectra of Mn in KMnF3

Abstract The L23 absorption spectrum as well as the photoexcited normal and resonant L23MM Auger spectra of Mn in KMnF3 are studied using synchrotron radiation. The absorption spectrum is very similar to the analogical spectrum of MnF2. The multiple-hole final states strongly contribute to the normal L23M23M23, L23M23M45, and L23M45M45 spectra. At the resonance excitation, a crystal-field-affected spectator structure appears in the L23M23M23 spectrum and, probably, in the L23M23M45 spectrum. The origin of this structure is discussed.