Nonradiative relaxation processes in molecular crystals

Internal conversion is the dominant relaxation channel from higher lying excited states in molecular crystals and involves the transfer of energy from the electronic system to the lattice. In this work, we present results from simulations of the nonradiative relaxation process with an emphasis on both intra- and interband transitions. We find the internal conversion process to be strongly nonadiabatic and the associated relaxation time in the case of large energy excitations to be limited by the transitions made between states of different bands.     

Manifestations of random lattice deformations in the spectra of crystals with rare earths ions

The splitting of zero-phonon lines of rare-earth impurity centers is observed in the optical spectra of dielectric crystals. It is shown that the primary contribution to such splitting comes from random deformations associated with point defects in the crystals.     

Nonradiative heterofusion of excitons in doped organic molecular crystals

The nonradiative heterofusion of a host exciton with a guest molecule electronic excitation resulting in a higher electronic neutral single excited state is examined theoretically in the doped organic molecular crystals. The heterofusion process is treated as a nonradiative spontaneous multi-lattice phonon transition of the crystal from the electronic double excited initial state to the electronic single excited final state under the action of the interaction between the host molecules and the guest molecule. Two heterofusion channels are considered: the first one resulting in a higher electronic excited state of the guest molecule and the second one resulting in a higher host exciton state. The corresponding rate constants are calculated and discussed within the framework of the first order time dependent perturbation theory.     

Nuclear orientation and NMRON in rare earths

The rare-earth or lanthanoid series of elements offers a rich ground for the study of both solid-state phenomena and nuclear physics. Some systematic investigations of these elements as host materials and as impurity isotopes have been performed using the nuclear orientation methods, and more can be expected in the near future owing to recent technical developments. A review of past work in this area is given, and the outlook for future experiments is summarized.     

Anisotropic k-ƒ interactions from spin-orbit coupled 5d intermediate states

The anisotropy of the conduction electron-4? local moment interaction ($\text{k-?}$) gives rise to anisotropic transport effects. The contribution from the orbital character of the 4? moment has been well documented by magnetotransport studies on noble metals containing non-S state rare-earth ions. To determine whether there is an additional contribution to the anisotropy from the spin-orbit coupled 5d electron states we have studied the magnetoresistivity of Ag: Gd alloys. We have not found any significant anisotropy of the magnetoresistivity. By comparing this result and previous Hall effect and magnetoresistivity data on noble metal-rare earth alloys with our model calculation, we come to the conclusion that the spin-orbit splitting of the 5d virtual bound state is relatively small. We discuss the details of the resulting anisotropy of the $\text{k-?}$ interaction.     

Nonradiative destruction of triplet excitons by excess electrons in organic crystals

The nonradiative destruction of triplet excitons by excess electrons in organic crystals is examined theoretically within the framework of the first-order time-dependent perturbation theory and within framework of the diffusion theory. The numerical calculations have been carried out for the anthracene crystal and compared with experiment.     

Theoretical study on decay of the 4d core-excited states of Cs III

In a recent XUV photoabsorption spectrum of Cs Ⅲ ions by Cummings and O＇Sullivan [2001 J. Phys. B 34 199], rather large linewidths were found for the 4d^95s^25p^6 - 4d^105s^25p^5 transition which are quite in disagreement with corresponding quasi-relativistic multiconfiguration Hartree Fock （MCHF） calculation. In the present work, a detailed multiconfiguration Dirac-Fock study has been carried out to explore this discrepancy. Owing to the detailed consideration of electron correlation effects, some ‘forbidden＇ Auger decay channels, such as 4d^105s^25p^35d and 4d^105s^05p^6, would become ‘open＇. As a result, remarkable improvement of the linewidths has been obtained in our calculation. Furthermore, the theoretical Auger spectrum of the 4d^ 95s^25p^6 core-excited states of Cs Ⅲ ions is Riven in the present work.     

Electrical resistivity of dilute heavy rare earths in Lu

The scattering of conduction electrons by the localized moments of heavy rare earth ions in Lu is investigated by analysing previously published resistivity measurements. The crystal field splitting of the 4f-levels is taken into account and satisfactory agreement obtained with experiment.     

A rare nuclear decay process: The internal conversion between bound atomic states

We shall report on the recently observed dependence of the lifetime of the first excited state in ¹²⁵Te on the ionic charge state. Then we shall give an interpretation of the dependence of the half-life in terms of a new type of nuclear internal conversion without emission of the electron into the continuum of electron energies. We have named this process internal conversion between bound atomic states or BIC. The resonant character of the BIC will be established and the main parameters governing the decay process will be discussed [1–3]. Finally the results of a recent experiment performed at the GANIL accelerator attempting to measure directly the value of the internal conversion coefficient associated with BIC in ¹²⁵Te ions with charge states ranging between 44+ and 48+ will be given. In conclusion we shall discuss the relation between the BIC and nuclear excitation by electron transition, NEET, in the excitation of some nuclear isomeric states.     

Luminescence decay in AgCl crystals

The kinetics of luminescence decay of single crystal plates of AgCl was measured at the temperature of liquid nitrogen. Luminescence decay first takes place (fort≦2·5× ×10^?3 sec) according to a hyperbole and then according to an exponential. The constantsa anda of the hyperbolic andt of the exponential dependence were measured for different intensity of the exciting radiation in normal and deformed samples and in samples irradiated withb-particles during measurement.     

Electron-transfer-mediated decay and interatomic Coulombic decay from the triply ionized states in argon dimers

We report the first observation of electron-transfer-mediated decay (ETMD) and interatomic Coulombic decay (ICD) from the triply charged states with an inner-valence vacancy, using the Ar dimer as an example. These ETMD and ICD processes, which lead to fragmentation of Ar(3+)-Ar into Ar(2+)-Ar(2+) and Ar(3+)-Ar+, respectively, are unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ETMD or ICD electron and the kinetic energy release between the two fragment ions are measured in coincidence.     

Nonradiative heterofission of guest molecule electronic excitations in doped organic molecular crystals

Formulae for the rate constants of the nonradiative heterofission of a guest molecule electronic excitation into one host molecule electronic excitation and one guest molecule electronic excitation in the doped organic molecular crystals are derived. The coherent and incoherent host exciton heterofission channels are considered. Formulae derived for the singlet host exciton heterofission channels are related to the measurable optical properties of the host and guest molecule of the crystal. The effects of the intramolecular vibration are discussed.     

Volume and heat of solution of hydrogen in rare earths from proton screening charges

In this work we determine some fundamental microscopic and macroscopic properties of rare earth-hydrogen (RE-H) systems. The behaviour of the electronic density variation of RE-H systems is obtained, using a program based on the density functional formalism. This information allows us to calculate the volume of solution of hydrogen in rare earths, as well as their heat of solution, and to compare with experimental results.