Theoretical analysis of the kinetics of low-temperature defect recombination in alkali halide crystals

We analyzed carefully the experimental kinetics of the low-temperature diffusion-controlled F, H center recombination in a series of irradiated alkali halides and extracted the migration energies and pre-exponential parameters for the hole H centers. The migration energy for the complementary electronic F centers in NaCl was obtained from the colloid formation kinetics observed above room temperature. The obtained parameters were compared with data available from the literature

Luminescence spectra and kinetics of disordered solid solutions

We have studied both theoretically and experimentally the luminescence spectra and kinetics of crystalline, disordered solid solutions after pulsed excitation. First, we present the model calculations of the steady-state luminescence band shape caused by recombination of excitons localized in the wells of random potential induced by disorder. Classification of optically active tail states of the main exciton band into two groups is proposed. The majority of the states responsible for the optical absorption corresponds to the group of extended states belonging to the percolation cluster, whereas only a relatively small group of “radiative” states forms the steady-state luminescence band. The continuum percolation theory is applied to distinguish the “radiative” localized states, which are isolated in space and have no ways for nonradiative transitions along the tail states. It is found that the analysis of the exciton-phonon interaction gives the information about the character of the localization of excitons. We have shown that the model used describes quite well the experimental cw spectra of CdS(1−c)Sec and ZnSe(1−c)Tec solid solutions. Further, the experimental results are presented for the temporal evolution of the luminescence band. It is shown that the changes of band shape with time come from the interplay of population dynamics of extended states and spatially isolated “radiative” states. Finally, the measurements of the decay of the spectrally integrated luminescence intensity at long delay times are presented. It is shown that the observed temporal behavior can be described in terms of relaxation of separated pairs followed by subsequent exciton formation and radiative recombination. Electron tunneling processes are supposed to be responsible for the luminescence in the long-time limit at excitation below the exciton mobility edge. At excitation by photons with higher energies the diffusion of electrons can account for the observed behavior of the luminescence

Anomalous diffusion-controlled kinetics in irradiated oxide crystals

MgO, Al2O3 and MgF2 are three wide gap insulating materials with different crystalline structures. All three materials are radiation resistant and have many important applications, e.g. in reactor optical windows. It is very important to predict their long-time defect structure evolution controlled by defect migration and reactions. One could estimate the diffusion coefficients of radiation defects in solids from measurements of the main defect concentration changes (oxygen vacancies called the F-type color centers, by optical absorption) under different conditions, e.g., sample heating (annealing) after irradiation

Anomalous diffusion-controlled kinetics in irradiated oxide crystals

MgO, Al2O3 and MgF2 are three wide gap insulating materials with different crystalline structures. All three materials are radiation resistant and have many important applications, e.g. in reactor optical windows. It is very important to predict their long-time defect structure evolution controlled by defect migration and reactions. One could estimate the diffusion coefficients of radiation defects in solids from measurements of the main defect concentration changes (oxygen vacancies called the F-type color centers, by optical absorption) under different conditions, e.g., sample heating (annealing) after irradiation

Synchronization of surface reactions via Turing-like structures

We discuss an alternative to the traditional gas-phase coupling approach in order to explain synchronized global oscillations in CO oxidation on Pt(110). We use a microscopic model which includes structural Pt surface reconstruction via front propagation, and large diffusion rates for CO. The synchronization mechanism is associated with the formation of a Turing-like structure of the substrate. By using large parallel microscopic simulations we derive scaling laws which allow us to extrapolate to realistic diffusion rates, pattern size, and oscillation periods