Interconfiguration

Wilson JA (1977) A Generalized Configuration - Dependent Band Model for Lanthanide Compounds and Conditions for Interconfiguration Fluctuations. 32 57-91 Wilson MR (1999) Atomistic Simulations of Liquid Crystals. 94 41-64 Winkler H, see Trautwein AX (1991) 78 1-96... 

The ionic case, for example NaCl Cu(I), is discussed in terms of transitions corresponding to an interconfigurational MC transition and... 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

Core-level spectra are useful in studying mixed valence (valence instability or interconfigurational fluctuation) in rare-earth systems (e.g. SmS, Ce) which arises when Eexc = n (E -i + FJ 0 where( — , )istheenergydifferencebetweenthe4/ and 4T states and is the energy of the promoted electron. The time scale involved... 

Dependent Band Model for Lanthanide Compounds and Conditions for Interconfiguration Fluctuations J. N Murrell The Potential Energy Surfaces of Polyatomic Molecules J-A-Duffy Optical Electron ativity and Nephelauxetic Effect in Oxide Systems Application to Conducting, Semi-Conducting and Insulating Metal Oxides... 

A Generalized Configuration-Dependent Band Model for Lanthanide Compounds and Conditions for Interconfiguration Fluctuations... 

The non-diagonal (with respect to configurations) operators that enter into (17.21) and (17.22) define the interaction between all the possible electron distributions over various two-shell configurations and give a nonzero contribution only for pertinent interconfiguration matrix elements. So, in the case of a superposition of configurations of the kind ni/f1 ni 2 - it is necessary to consider only the following terms of... 

Such general expressions for matrix elements of electrostatic interactions, covering the cases of three and four open shells, may be found in Chapter 25 of [14]. However, they are rather cumbersome and, therefore of little use for practical applications. Quite often sets of simpler formulas, adopted for particular cases of configurations, are employed. Below we shall present such expressions only for the simplest interconfigurational matrix elements occurring while improving the description of a shell of equivalent electrons (the appropriate formulas for the more complex cases may be found in [14]) ... 

The interconfigurational 4/"-4/n 15d transitions are of a different nature. They are parity allowed and can be described with the intermediate-coupling model, i.e. 1 < S < 5. In some cases a beautiful vibrational structure with a short progression has been observed. 

In this paragraph we will discuss two types of optical transitions in the transition metal ions first the intraconfigurational dn transitions, second the interconfigurational charge-transfer transitions in complexes with a d° central metal ion. 

Many models have been postulated to account for the interconfiguration fluctuations (ICF) in rare earth intermetallic compounds. We will consider Hirst s model which assumes that the 4/ electrons are highly correlated and preserve their atomic-like features during the valence fluctuation. Both the X-ray photoelectron spectra and the magnetic susceptibility of rare earth intermetallic compounds can be successfully explained on the basis of Hirst s model [8,11]. 

According to the model the period r of the interconfigurational fluctuation is given by the width, d ( hr) of the principal band. The average valence V is given by... 

The methods by which the phenomenon of interconfiguration fluctuations may be studied are (i) determination of lattice constant, (ii) magnetic susceptibility measurements, (iii) Mossbauer spectroscopy, (iv) measurement of electrical resistivity, (v) Hall effect, (vi) X-ray absorption spectroscopy and (vii) X-ray photoelectron emission spectroscopy. It is useful to note that a suite of techniques must be used to detect ICF phenomenon in a system. Nuclear magnetic resonance is sparingly used because not all the systems exhibiting ICF contain magnetically active nuclei. 

J.A. Wilson, A generalized configuration-dependent band model for lanthanide compounds and conditions for interconfiguration fluctuations, pp. 58-90, Bell Laboratories, Murray Hill, New Jersey 07974. 

The second chapter deals with quantum chemical considerations, s, p, d and f orbitals, electronic configurations, Pauli s principle, spin-orbit coupling and levels, energy level diagrams, Hund s mles, Racah parameters, oxidation states, HSAB principle, coordination number, lanthanide contraction, interconfiguration fluctuations. This is followed by a chapter dealing with methods of determination of stability constants, stability constants of complexes, thermodynamic consideration, double-double effect, inclined w plot, applications of stability constant data. 

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