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Using the spin-Hamiltonian formalism the magnetic parameters are introduced through the components of the Λ-tensor involving only the matrix elements of the angular momentum operator. The energy levels for a variety of spins are generated, and the modeling of the magnetization, the magnetic susceptibility, and the heat capacity is done. Theoretical formulae necessary for performing the energy level calculations for a multiterm system are prepared with the help of the irreducible tensor operator approach. The goal of the programming is to evaluate the entire relevant matrix element (electron repulsion, crystal field, spin–orbit interaction, orbital-Zeeman, and spin-Zeeman operators) in the basis set of free-atom terms. The modeling of the zero-field splitting is done at three levels of sophistication: (i) the differences in the crystal-field multiplets when the high-dimensional matrix in the complete space is diagonalized; (ii) the differences in the energy levels of a model subspace when the partitioning technique is applied in the first iteration; (iii) the differences in the energy levels as they are produced by the second-order perturbation theory for the spin Hamiltonian. The spin-Hamiltonian formalism offers simple formulae for the magnetic parameters (the D-factors , D-parameter, χTIP) by evaluating the matrix elements of the angular momentum operator in the basis set of the crystal-field terms. The magnetic functions for dn complexes are modeled for a wide range of crystal-field strengths. [ABSTRACT FROM AUTHOR]

Synthesis of high quality semiconductor nanocrystals is discussed in this chapter. Although the focus is on the recent progress in synthesis of colloidal semiconductor nanocrystals in non-aqueous solution, there is some review of the historical development of the aqueous and other approaches. Mechanisms for controlling the shape, size, and optical properties of colloidal semiconductor nanocrystals are described in detail, although for the most part this topic can only be treated on a qualitative level. Finally, one area of study, the formation of nanocrystals, is discussed in terms of its practical and fundamental significance. [ABSTRACT FROM AUTHOR]

The structures of ternary and quaternary silicates are revisited on the basis of the Zintl-Klemm concept and the Pearson's generalised octet rule. The three-dimensional skeletons formed by the Si atoms can be interpreted as if the Si atoms were behaving as Zintl polyanions, adopting the structure of either main-group elements or Zintl polyanions showing the same connectivity. The O atoms are then located close to both, the hypothetical two-electron bonds and the lone pairs, giving rise to a tetrahedral coordination. In some silicates, the Si atoms clearly show an amphoteric character so that some Si atoms act as donors (bases) adopting an octahedral coordination, whereas others behave as acceptors (acid), adopting a tetrahedral coordination. Although the octahedral coordination seems to be favoured by the application of pressure, the results reported here indicate that the coordination sphere of silicon is not a function of the assumed ionic radius of the Si4+ cations but it depends on the nature of the other cations accompanying them in the structure. [ABSTRACT FROM AUTHOR]

This chapter reviews intraband spectroscopy as it has been applied to semiconductor nanocrystals synthesized by colloid methods. [ABSTRACT FROM AUTHOR]

A retrospective overview of electrochemical studies of semiconductor nanocrystals (NCs) is given. The electrochemical behavior of monodisperse NCs in a non-aqueous supporting electrolyte can be derived from the electron quasiparticle energy and the electron self-energy. Coulomb blockade can sometimes be observed in Si NCs if the charged NCs are stable. Many NCs, such as Ge, CdS, CdSe, PbS and core-shell CdSe/ZnS undergo some electrochemical and chemical reactions such as the so-called EC reaction mechanism. Electrogenerated chemiluminescence (ECL) processes for elemental and II/VI compound NCs in solution (and their films) are found to follow the general ECL mechanisms of organic compounds. Most NCs emit ECL, which is red-shifted into the photoluminescence (PL) region. ECL studies of NC solid-state films, especially the combination of organic light-emitting diodes (LEDs) and NCs, have suggested the potential for real workable devices. Treated CdSe NC thin films also exhibit stable and fast electrochromic changes and ECL. [ABSTRACT FROM AUTHOR]

The properties of the actinides in the first half of the series are deduced from the characteristics of 5f wavefunctions, in many ways similar to the d-wavefunction in transition metals. Relativistic effects and the calculation of ground state properties are stressed. [ABSTRACT FROM AUTHOR]

Localization versus itineracy and the degree of hybridization of 5 f states with orbitals of the actinide atom (especially 6 d) as well as with those of the ligand in compounds are central questions for the understanding of bonding in actinide solids. Photoelectron spectroscopy provides answers to these questions. In narrow band solids, like the actinides, the interpretation of results requires the use of band calculations in the itinerant picture, as well as models of final state emission in the atomic picture. From the experimental viewpoint: l. the analysis of the variation of photoionization cross sections (affecting the intensities of photoelectron spectroscopy), gives an insight into the orbital composition of the bands of the solid; 2. the combination of direct and inverse photoemission provides a powerful tool to assess the structure of occupied and of empty states, and, in the case of localized 5 f states, permits the determination of a fundamental quantity, the Coulomb correlation energy, governing the physical properties of narrow bands. After a survey of the basic theory and some experimental aspects of photoelectron spectroscopy which are relevant to actinide solids, two systems are illustrated: elemental actinide metals, in which the Mott transition between plutonium and americium is evidenced in a "photographic" way by photoemission, and strongly ionic oxides, in which the 5 f localized behaviour is clearly seen, and indications of f-p or d-p covalent mixing are investigated. [ABSTRACT FROM AUTHOR]

The various magnetic properties observed in actinide solids are largely determined by the degree the unsaturated 5 f shells retain an atomic localized character or lose it in an itinerant mode. Hence the investigation of magnetism (and of related properties such as low temperature electrical resistivity) has played a central role in understanding bonding in actinide solids. Between clear cut cases of "localization" or "itineracy" intermediate situations are observed (leading for instance to spin fluctuating behaviour) which have made actinide magnetic research a rich but also controversial field. A short exposition of the basic concepts of actinide magnetic research and of the different aspects of magnetic ordering in actinide solids is followed by a discussion of experimental and interpretational aspects, in particular the difficulty always encountered of separating the different contributions. A number of examples have been chosen to illustrate the variety of magnetic behaviour and its meaning in establishing a unified picture of actinide solid state physics. One of the aims of the chapter is to inspire new research in actinide magnetism. To this purpose, tables collecting the main magnetic data for a large number of actinide binary compounds are provided. [ABSTRACT FROM AUTHOR]

The problem of bonding in actinide solids has been approached through the establishment of semi-theoretical correlations between thermodynamic and structural properties and the degree of participation to the bond of the different electronic orbitals of the actinide atom. The first part of the chapter is devoted to an analysis of these correlations, as well as to the presentation of the most important experimental results. In a second part the following stage of development is reviewed, i.e. the introduction of more quantitative theories mostly based on bond structure calculations. These theories are given a thermodynamic form (equation of states at zero temperature), and explain the typical behaviour of such ground state properties as cohesive energies, atomic volumes, and bulk moduli across the series. They employ in their simplest form the Friedel model extended from the d- to the 5 f-itinerant state. The Mott transition (between plutonium and americium metals) finds a good justification within this frame. In actinide binary compounds an equation of state can also be developed on the same lines. The difference in electronegativity of the actinide and the non-actinide element plays an important role, determining the degree of mixing between the actinide orbitals (5 f and 6 d) and the orbitals of the ligand. A mixture of metallic, ionic and covalent bond is then encountered. In the chapter, two classes of actinide compounds are reviewed: NaCl-structure pnictides or chalcogenides, and oxides. In oxides a large departure from the stoichiometric composition is usually met. The importance of this phenomenon, also for the understanding of the oxide bond, is highlighted at the end of the chapter. [ABSTRACT FROM AUTHOR]

Considerable progress has been possible in the determination of chemical and physical properties of actinide solids as a result of improved preparation and purification methods. The growing demands for well characterized samples have given the incentive to overcome the difficulties presented to the actinide chemist by the high radioactivity hazard and comparative rarity of the actinide elements. In this chapter, preparation and purification methods are reviewed. In view of the expected role of 5 f electrons in the metallic bond of actinides, methods for the preparation of metals have been particularly studied. There has also been important progress in the preparation of simple binary compounds. Special emphasis has been given to the growth of single crystals, particularly needed for the most refined physical techniques. The chapter underlines the interdisciplinary nature of actinide solid state research. [ABSTRACT FROM AUTHOR]