Europium electron system

A systematic study of the luminescent characteristics of glasses containing rare earths was done in this laboratory (14—20). There has been considerable spectroscopic investigation involving europium activated phosphors for several reasons. The phosphors are of practical use in color television and more information about crystal levels can be obtained for even-electron systems than those with odd-electron systems. Reisfeld et al. (21—25) and Rice and DeShazer (26) have used the fluorescence of europium as an indicator of site S5nnmetry of rare earth ions in glasses. 

Rare earth dicarbides are commonly formed in the rare-earth (except for europium)-carbon systems. Many investigators, in particular Atoji, have made a great contribution to the determination of the structure of RC2. The neutron diffraction investigations on the structure of the rare earth dicarbide, first by Atoji and Medrud (1959) showed that for the lanthanum dicarbide the atomic coordinates in the unit cell are (000, ) + (OOz) for carbon atoms and z = 0 for lanthanum atoms, and the carbon positional parameter z(A) is 0.403 + 0.002, corresponding to a well-defined minimum at a C-C distance of 1.28 0.03 A. LaC2 can probably be described approximately in terms of ions, with the extra electron in a conduction... 

Reductions of monosubstituted iron(iii) complexes have been studied, the reactions being inner sphere with rates in the order Br > Cl > F" in contrast to the corresponding europium(ii) systems. The order does, however, parallel that for the Cr reduction of pentammine-cobalt(m) halide complexes. Reactions with platinum(iv) complexes have been studied, and in the case of [Pt(NH3)sa] + and [Pt(NH3)sOH] + a two-electron change is involved with intermediate formation of Cr and subsequent production of dimeric Cr" complexes ... 

A dye molecule has one or more absorption bands in the visible region of the electromagnetic spectrum (approximately 350-700 nm). After absorbing photons, the electronically excited molecules transfer to a more stable (triplet) state, which eventually emits photons (fluoresces) at a longer wavelength (composing three-level system.) The delay allows an inverted population to build up. Sometimes there are more than three levels. For example, the europium complex (Figure 18.15) has a four-level system. 

This chapter commences with a review of a limited number of ternary hydride systems that have two common features. First, at least one of the two metal constituents is an alkali or alkaline earth element which independently forms a binary hydride with a metal hydrogen bond that is characterized as saline or ionic. The second metal, for the most part, is near the end of the d-electron series and with the exception of palladium, is not known to form binary hydrides that are stable at room temperature. This review stems from our own more specific interest in preparing and characterizing ternary hydrides where one of the metals is europium or ytterbium and the other is a rarer platinum metal. The similarity between the crystal chemistry of these di-valent rare earths and Ca2+ and Sr2+ is well known so that in our systems, europium and ytterbium in their di-valent oxidation states are viewed as pseudoalkaline earth elements. 

Tn accordance with its electronic configuration and the resulting posi-tion in the periodic system of elements the actinide element americium is the heavy homolog of the rare earth element europium (14) ... 

A systematic study of the Eu/Yb and Eu/Ba alloys has been made [52, 53]. In the ytterbium system, the Curie temperature falls from 90 to 5 K and the saturation field also falls from 265 to 160 kG as the ytterbium content increases from 0 to 92 at. %. The relationships are linear apart from a discontinuity at 50 at. % where there is a phase change. Similarly for barium the Curie temperature falls from 90 to 40 K and the field from 265 to 206 kG as the barium content rises to 50 at. %. However, the chemical isomer shift is not significantly altered. The sign of the magnetic field is known to be negative from neutron diffraction data. Calculations suggest that a contribution of —340 kG to the field in europium metal arises from core polarisation, that +190 kG comes from conduction-electron polarisation by the atoms own 4/-electrons, and that —115 kG comes from conduction-electron polarisation, overlap, and covalency effects from neighbouring atoms. 

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