Transition Metals and Rare Earths

Simple metals like alkalis, or ones with only s and p valence electrons, can often be described by a free electron gas model, whereas transition metals and rare earth metals which have d and f valence electrons camiot. Transition metal and rare earth metals do not have energy band structures which resemble free electron models. The fonned bonds from d and f states often have some strong covalent character. This character strongly modulates the free-electron-like bands. 

Gamelin DR, Gudel HU (2001) Upconversion Processes in Transition Metal and Rare Earth Metal Systems. 214 1-56 Ganachaud F, see Elaissari A (2003) 227 169-193 Garda R, see Tromas C (2002) 218 115-132 Geraldes CFGC, see Frullano L (2002) 221 25-60... 

Transition Metal and Rare Earth Compounds III Volume Editor Yersin, H. 

Gamelin DR, Gudel HU (2001) Upconversion Processes in Transition Metal and Rare Earth Metal Systems. 214 1 - 56... 

TRANSFORMATIONS OF ORGANO COMPOUNDS TRIGGERED BY THE INTERACTION WITH TRANSITION METAL AND RARE EARTH SYSTEMS... 

Wang Y, Yin L, Gedanken A (2002) Sonochemical synthesis of mesoporous transition metal and rare earth oxides. Ultrason Sonochem 9(6) 285-290... 

Transition-metal and rare-earth atoms that contain partially occupied d or f valence subshells also give rise to spectral tine structure, often with very complicated multiplet splitting [2,27,28]. The spin-unpaired valence d or f electrons can undergo spin-orbit coupling with the unpaired core electron (remaining in the orbital from which the photoelectron was removed), producing multiple non-degenerate final states manifested by broad photoelectron peaks [2,27]. 

The transition-metal and rare-earth core-line XPS spectra show little, if any, BE shifts at all. Nevertheless, information about atomic charge and valence states can be extracted by examining other features in the spectra. The plasmon loss satellite intensity found in the spectra of Co-containing compounds provides a particularly useful handle on the Co charge. The lineshapes of RE spectra are characteristic of their valence state, as seen in the distinction between trivalent and tetravalent cerium in CeFe4Pni2 compounds. 

In principle, all of the elements of the periodic table can be used to iucorporate foreign ions in crystals. Actually, only a number of elements have been used for optically active centres in crystals in other words, only a number of elements can be incorporated in ionic form and give rise to energy levels within the gap separated by optical energies. The most relevant centers for technological applications (although not the unique ones) are based on ions formed from the transition metal and rare earth series of the periodic table, so we will focus our attention on these centers. 

Moreover, the analysis of the optical spectra of transition metal and rare earth ions is very illnstrative, as they present qnite different features due to their particular electronic configurations transition metal ions have optically active unfilled outer 3d shells, while rare earth ions have unfilled optically active 4f electrons screened by outer electroiuc filled shells. Because of these unfilled shells, both kind of ion are usually called paramagnetic ions. 

The ZSA phase diagram and its variants provide a satisfactory description of the overall electronic structure of stoichiometric and ordered transition-metal compounds. Within the above description, the electronic properties of transition-metal oxides are primarily determined by the values of A, and t. There have been several electron spectroscopic (photoemission) investigations in order to estimate the interaction strengths. Valence-band as well as core-level spectra have been analysed for a large number of transition-metal and rare-earth compounds. Calculations of the spectra have been performed at different levels of complexity, but generally within an Anderson impurity Hamiltonian. In the case of metallic systems, the situation is complicated by the presence of a continuum of low-energy electron-hole excitations across the Fermi level. These play an important role in the case of the rare earths and their intermetallics. This effect is particularly important for the valence-band spectra. 

Murphy and co-workers (119) have reported the transfer of energy from 3d to 4/electrons in LaA103 Cr Nd, and studied the fluorescent lifetimes of both the transition-metal and rare-earth ion. Their evidence for transfer was that neodymium fluorescence was excited when the sample was pumped in a region where only the chromium adsorbs. The series of compounds investigated was La1 A.NdArAlI >,Cr>,03. They observed that the intensity of the chromium fluorescence decreases rapidly with neodymium... 

Yersin H (2004) Transition Metal and Rare Earth Compounds Iii (Topics in Current Chemistry) 241 1-26... 

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