Die Verf�rbung von MgO-Kristallen durch gittereigene Bausteine

Weber, Heinrich

doi:10.1007/bf01340175

Cited by 79 publications

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“…4 This is supported by model studies of the kinetics of F-center aggregation. 5 However, while some author has reported similar bands at 3.5 and 2.1 eV in additive coloring experiments, 6 Chen et al were not able to observe these transitions in electron irradiated additive colored samples. 3 X ray 7 and UV ͑Ref.…”

Section: Introductionmentioning

confidence: 96%

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Ground- and excited-state properties ofM-center oxygen vacancy aggregates in the bulk and surface of MgO

et al. 2003

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Aggregates of oxygen vacancies ͑F centers͒ represent a particular form of point defects in ionic crystals. In this study we have considered the combination of two oxygen vacancies, the M center, in the bulk and on the surface of MgO by means of cluster model calculations. Both neutral and charged forms of the defect M and M ϩ have been taken into account. The ground state of the M center is characterized by the presence of two doubly occupied impurity levels in the gap of the material; in M ϩ centers the highest level is singly occupied.For the ground-state properties we used a gradient corrected density functional theory approach. The dipoleallowed singlet-to-singlet and doublet-to-doublet electronic transitions have been determined by means of explicitly correlated multireference second-order perturbation theory calculations. These have been compared with optical transitions determined with the time-dependent density functional theory formalism. The results show that bulk M and M ϩ centers give rise to intense absorptions at about 4.4 and 4.0 eV, respectively. Another less intense transition at 1.3 eV has also been found for the M ϩ center. On the surface the transitions occur at 1.6 eV (M ϩ ) and 2 eV ͑M͒. The results are compared with recently reported electron energy loss spectroscopy spectra on MgO thin films.

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Section: Introductionmentioning

confidence: 96%

“…At the CASPT2 level three clusters of different shape and size have been used for bulk F centers: Mg 6 Different basis sets have been used in the CASPT2 and DFT calculations. This is due to the slower convergence towards basis set limit of the explicitly correlated calculations compared to DFT calculations.…”

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confidence: 99%

Ground- and excited-state properties ofM-center oxygen vacancy aggregates in the bulk and surface of MgO

et al. 2003

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“…Anion vacancies also called color centers or F-centers in the bulk of MgO and other alkaline earth oxides have been studied comprehensively in the past using EPR as well as optical spectroscopy, see e.g. [3,[10][11][12]. A variety of studies has been published on the nature and properties of their surface analogs often called F s -centers on powdered material [13][14][15][16][17][18][19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Characterization of O−-Centers on Single Crystalline MgO(001)-Films

et al. 2015

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Defects play an important role for understanding the properties of oxide surfaces. However, a detailed atomistic characterization of the properties of defects in particular of point defects is still a challenging task. On polycrystalline material it is the large variety of different species in terms of local environment, electronic properties as well as the metastable nature of most of these species, which complicates matters. EPR spectroscopy has proven to be a versatile tool to characterize electronic properties as well as local environment of paramagnetic point defects on oxide surfaces. In this study we elucidate the properties of O --centers on MgO surfaces under ultrahigh vacuum (UHV) conditions using a single-crystalline MgO(001) surface as a well-defined model system. The O --centers were produced by reaction of N 2 O with previously prepared F ? -centers, which were shown to be located at step edges of the MgO islands in a previous study. The experimental efforts are combined with ab-inito quantum chemistry calculations to gain a more detailed understanding of the electronic properties of the defects under consideration. The experimental and theoretical values of the g-tensor components are almost in quantitative agreement. In addition to the discussion of the properties of O --centers the paper will shed some light on the impact that doping of the surface in this case with Mo(V)-species present on the pristine surface has. In particular, we are able to provide evidence for the fact that there is redox chemistry between the O --centers and Mo-centers. The crosstalk between different redox active sites on the surface is an important phenomenon that is not limited to model systems as discussed here, but should also be taken into consideration if discussing the properties of high performance catalysts.

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“…The investigation of bulk point defects in ionic crystals is a milestone of solid state physics [1][2][3][4]. Among the many types of point defects investigated in detail, bulk F centers (excess electron centers) have attracted the most attention.…”

Section: Introductionmentioning

confidence: 99%

“…The addition of CO(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) to the Mg doped sample at ambient temperature results in the immediate disappearance of the blue violet color followed EPR spectra of species A (CO -) (a) and species B (C 2 Oz) (b) obtained by "CO adsorption on the electron rich surface of MgO at different temperature.…”

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confidence: 99%

Generation and EPR characterization of color centers at the surface of ionic oxides

et al. 1998

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The activation of the surface of high surface area alkali-earth oxides to form surface color centers is described in detail. Two methods (the radiative coloring and the additive coloring by means of vapors of low ionization energy metals) have been adopted to form surface electron excess centers of various complexity. The EPR technique is essential to describe the nature and the structural features of the paramagnetic centers. The electron rich surface quickly reacts with a variety of adsorbed molecules forming adsorbed anions and radical anions. Two examples of such reactivity are illustrated in the final part of the paper.

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Die Verf�rbung von MgO-Kristallen durch gittereigene Bausteine

Cited by 79 publications

References 0 publications

Ground- and excited-state properties ofM-center oxygen vacancy aggregates in the bulk and surface of MgO

Ground- and excited-state properties ofM-center oxygen vacancy aggregates in the bulk and surface of MgO

Characterization of O−-Centers on Single Crystalline MgO(001)-Films

Generation and EPR characterization of color centers at the surface of ionic oxides

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