Europium divalent

Divalent europium-activated BaECl was the first rare-earth-activated x-ray phosphor (24). The advantage of BaECLEu " over the conventional CaWO material is in the higher x-ray absorption and better x-ray-to-visible light conversion. The problem with BaECl for x-ray appHcation is in the lower density (4.56 g/cm vs 6 g/cm for CaWO and plate-like morphology. 

Most monochalcogenides of the Group 3 metals adopt the rock salt (NaCl) structure. Note that the crystal chemistry of divalent europium is very similar to that of the alkaline earths, particularly strontium, as the radius of Eu is almost the same as that of Sr ". For the Yb compounds, the cell dimensions are practically identical with those of the Ca compounds. 

EXAFS study on Eu2+ and Sr2+ in both solid state and aqueous solution gave coordination numbers of 8.0 for strontium(II) and 7.2 for europium(II) (228). The water exchange rate measured on the divalent europium aqua ion is the fastest ever measured by 170 NMR (Table XVI) (2). The activation volume is much more negative (—11.7 cm3 mol-1) than those determined on trivalent lanthanide aqua ions clearly indicating an a-activation mechanism which is most probably a limiting... 

After X-ray irradiation of thermally annealed NaCl crystals, a small percentage of divalent europium ions are converted into trivalent europium ions (Aguilar et al, 1982). This is shown by the appearance of weak and narrow absorption lines at around 460 nm and 520 nm, related to the Fq D2 and Fq Di transitions of Eu + ions, respectively. For our purposes, this example allows us to compare the different band features between (RE) + and (RE) + ions Eu + ions show broad and intense optical bands (electric dipole allowed transitions), while Eu + ions present narrow and weak optical lines (forced electric dipole transitions). 

Divalent europium is detected in apatite as a shoulder of Ce luminescence when studied by steady-state spectroscopy (Tarashchan and Marfunin 1969 ... 

The luminescence center of divalent europium in fluorite is well known (Haber-land et al. 1934 Tarashchan 1978 Krasilschikova et al. 1986 Barbin et al. 1996). It is clearly seen in laser-induced time-resolved luminescence spectra with a decay time of 600-800 ns (Fig. 4.10a). In several samples the band with a spectrum similar to those of Eu + has a very long decay time and remains even after a delay of several ms. Principally it may be connected with energy migration from a UV emitting center with a long decay time, for example, Gd ". ... 

Shown in Figure 7 is the emission spectrum for BaFCI.05Eu. The divalent europium emission is a broad band peaking at about 380 nm. This phosphor is used in DuPont Co. Quanta II blue screens and is useful with blue film only. 

Billard, L, Moutiers, G., Label, A., El Azzi, A., Gaillard, C., Mariet, C., and Lutzenkirchen, K., Stability of divalent europium in an ionic liquid spectroscopic investigations in l-methyl-3-butylimidazolium hexafluorophosphate, Inorg. Chem., 42,1726-1733,2003. 

Urbain and Botjrion [186] first prepared the divalent europium salt EuGla. In weakly acidic aqueous solution Eu2+ is quite stable in the absence of oxidizing agents. The divalent ions of Sm, Eu and Yb are strong reducing agents and follow the order Sm2+ > Yb2- > Eu2+. The oxidation potentials (E°) for the reaction... 

In 1939 Klemm and Doll [276] prepared all the halides of divalent europium and studied the magnetic characteristics of these compounds. The magnetic susceptibilities (X g) and effective moments of the fluoride, chloride, bromide and iodide are tabulated in Table 15. Except for the... 

This work was undertaken as a part of a study of divalent lanthanide halides in an effort to obtain more accurate thermal data on EuC12 and to determine if the close similarity of the high-temperature thermodynamic properties of divalent europium and alkaline earth compounds emphasized earlier (13-16) could be extended. 

In the case of the Eu(II) luminescence in methanol, the available data, that refer to the lifetime increase through complexation (see sect. 5) have been tentatively explained within the frame of OH bonds exclusion from the first Eu(II) solvation shell. Interestingly, the values of tobs and rrad for various Eu(II) complexes in methanol were obtained. The discussion above has shown the great interest of such measurements which, in the case of Eu(II), are difficult to perform due to the instability of divalent europium, and which should be more systematically performed in the case of trivalent europium. As compared to the solvated Eu2+ ion... 

Calculations of divalent europium ions in BAM phosphor 4.3.1. The BAM phosphor... 

W. J. Evans, M. A. Johnston, M. A. Greci, and J. W. Ziller, Synthesis, Structure, and Reactivity of Unsolvated Triple-Decked Bent Metallocenes of Divalent Europium and Ytterbium, Organometallics 18, 1460-1464 (1999). 

J. Jiang, N. Higashiyama, K.I. Machida, G.Y. Adachi, The luminescent properties of divalent europium complexes of crown ethers and cryptands, Coord. Chem. Rev. 170, 1-29, 1998. 

Ba (CN 6) 1.49 A, EN = 0.97) leads to chemistry dominated by electrostatic interactions. There are significant similarities between the chemistry of calcium and divalent ytterbium as well as strontium and divalent europium and samarium owing to quite similar size/charge ratios. SeeScandium, Yttrium the Lanthanides Organometallic Chemistry and Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry)... 

Until 1960 only samarium, europium, and ytterbium were indisputably known to exist in the divalent state. Divalent samarium was first isolated in 1906 by Matignon and Gazes (17). Divalent europium was found in 1911 by Urbain and Bourion (22). In 1929 Klemm and Schuth... 

The luminescence of divalent europium crown complexes in various solvents has been studied at various temperatures and the results correlated with structural differences of the complexes. 

Fig. 17.8 Chemical isomer shifts of divalent europium selenides correlated with the mean Eu -Se " distance. [Ref. 31, Fig. 3]...

Mayer I, Fischbein E, Cohen S (1975) Apatites of divalent europium. J Solid State Chem 14 307-312 Mayer I, Semadja A (1983) Bismuth-substituted calcium, strontium, and lead apatites. J Solid State Chem 46 363-366... 

Palilla FC, O Reilly BE (1968) Alkaline-earth halophosphate phosphors activated by divalent europium. J Electrochem Soe 115 1076-1081... 

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