摘要:

Dipole aggregation in rare-earth-doped fluorides, using the HADES code to calculate the energies of the defects was extensively studied. The binding energy values determined for dipoles and dimers agree quite well with published data. The possibility of creation of mixed dimers took into account the size of the impurities and also the electronic configuration. The results obtained confirmed that binding energies depend upon the ionic radius of the impurities and revealed a preferential order for the formation of mixed dimers. For the impurities with ionic radii larger than or very near to that for calcium the chance of forming mixed dimers is greater than for smaller impurities. The obtained values of the energies confirm the possibility of mixed dimer creation although simple dimers are preferentially formed first.

ISSN:1042-0150    

DOI:10.1080/10420159508227195

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The local arrangement of a substitutional Cr3+ion for an Al3+ion in corundum is studied by means of first-principles pairwise simulations and quantum-mechanicalab initioPerturbed Ion calculations. Our investigation is organized in two steps. First, we determine the cohesive properties of the host lattice by calculating the set of four crystalline parameters that makes minimum the total energy of corundum. Secondly, we solve cluster models of increasing complexity centered at the Cr3+site and embedded in the previously computed crystal potential. This is a consistent strategy that contributes to determine the local geometry of Cr3+in α-Al2O3.

ISSN:1042-0150    

DOI:10.1080/10420159508227196

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Local distortions and optical properties induced by the substitutional Cr3+impurity in the MgO host lattice are computed using the embedded cluster approach implemented in the ICECAP (ionic crystal with electronic cluster, automatic program) code. Our calculations predict inward relations of the six O2−nearest neighbors surrounding the Cr3+ion for both cubic and noncubic (tetragonal and orthorhombic) configurations in MgO. For the cubic configuration, selected low-lying excited states, including the 10 Dq generator4T2, are calculated at several Cr-O separations. After taking into account lattice relaxations and correlation corrections, the computed 10 Dq value lies 0.19 eV lower than the experimental one.

ISSN:1042-0150    

DOI:10.1080/10420159508227197

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The cooperative effect is studied in the kinetics of bimolecular A+B→O reactions between charged particles (reactants). Unlike the Debye-Hückel theory, charge screening has an essentially non-equilibrium character. The reaction rate does not approach a steady state, but increases infinitely in time for the asymmetric mobility of reactants (DA=O, DB≠O).

ISSN:1042-0150    

DOI:10.1080/10420159508227198

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We introduce a stochastic model for the A + B → O reaction on a discrete lattice. The system may include mono- and bimolecular steps (i. e. reaction and diffusion steps). The resulting infinite chain of equations is truncated at a certain level via a modified Kirkwood approximation.

ISSN:1042-0150    

DOI:10.1080/10420159508227199

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

For the Relaxed Excited States of the F-centre, the simplest vibronic model involves only the Γ−4; mode in the electron-lattice interaction HeL. In analyzing the perturbation correction due to HeL, Ham and Grevsmühl kept only the linear terms in the coupling constant G and ended up with a positive value for the field-induced shift in the energy of the parallel component in emission δE∥,—in disagreement with the experiments. In this paper, it is shown that when the perturbation correction terms are kept up to G2, δE∥, is negative.

ISSN:1042-0150    

DOI:10.1080/10420159508227200

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this communication we present a simple, semi-empirical model of the three center Auger effect (TCAR). It is based on the dipole approximation of the interaction Hamiltonian. Application of this model to the case of TCAR in ZnS:Fe yields the value of critical distance for the energy transfer about 10 Å.

ISSN:1042-0150    

DOI:10.1080/10420159508227201

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

TL glow curves were computer simulated for Randall-Wilkins, Garlick-Gibson, May-Patridge and Adirovitch models in a range of activation energies (0.1 to 2.0 eV) which were afterwards recovered by the initial rise method. The systematic error of the recovered energies is always the same independent of the energy used in the simulated curves. It was found that there is no dependence of the error onto the heating rate and there is a dependence of error curves on the models used in computer simulated TL emission. A correction factor can be plotted against the percentage of the peak maxima used in the initial rise for each model and we could apply it even if more than 50% of the ascending part of the glow peak has to be considered.

ISSN:1042-0150    

DOI:10.1080/10420159508227202

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An excess-electron point defect associated with an oxygen vacancy as observed in paratellurite has been modeled and studied using theab initioRHF-SCF molecular orbital method of the Many ELectron Description (MELD) program package. Open-shell electronic structure calculations for obtaining spin densities were performed on molecular clusters Te2O6H6having paratellurite geometry and terminated by hydrogen-like atoms with optimized nuclear charges and O-H distances. Hyperfine and superhyperfine matrix elements were calculated based on the spin densities of theab initioresults, and the effects of spin delocalization, second-order perturbation magnetic contributions, extended CI calculations, double-zeta quality basis functions and defect-centered basis functions on these parameters were investigated. While specific results in excellent agreement with EPR measurements were obtained and strongly support the proposed defect model, inability to obtain overall agreement with experiment via a single calculation is suggestive of limitations resulting from cluster size as well as basis set quality and size.

ISSN:1042-0150    

DOI:10.1080/10420159508227203

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have modelled cationic Frenkel defects, Schottky defects and bound vacancy pairs in AgBr according to the recently introduced EPPI model. Our findings suggest a significant role for Schottky defects in the excess high temperature conductivity and also an important role for bound vacancy pairs in anion self-diffusion.

ISSN:1042-0150    

DOI:10.1080/10420159508227204

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor