Europium impurity

In order to make an efficient Y202 Eu ", it is necessary to start with weU-purifted yttrium and europium oxides or a weU-purifted coprecipitated oxide. Very small amounts of impurity ions, particularly other rare-earth ions, decrease the efficiency of this phosphor. Ce " is one of the most troublesome ions because it competes for the uv absorption and should be present at no more than about one part per million. Once purified, if not already coprecipitated, the oxides are dissolved in hydrochloric or nitric acid and then precipitated with oxaflc acid. This precipitate is then calcined, and fired at around 800°C to decompose the oxalate and form the oxide. EinaHy the oxide is fired usually in air at temperatures of 1500—1550°C in order to produce a good crystal stmcture and an efficient phosphor. This phosphor does not need to be further processed but may be milled for particle size control and/or screened to remove agglomerates which later show up as dark specks in the coating. 

The purest grade of europium metal available from the Lindsay Chemical Division of American Potash is 99.9% Eu in terms of rare earth content, but it may contain up to 1% of other metal impurities (mainly tantalum when prepared in tantalum vessels) and typically contains 2.8 mol % oxygen.6... 

They illustrated the effects of impurities by data taken on europium tris-benzoylacetonate (EuBA), europium tris-dibenzoylmethide (EuD3), and terbium tris-acetylacetonate (TbAA) chelates. 

It has been found that in the preparation of pure europium the starting materials need not be extremely pure. The common impurity viz. samarium is completely eliminated in the above process because samarium is less volatile than europium, and the reduction of Sn Os to the metal requires a higher temperature than the EU2O3 reduction. Commeri-cal lanthanum turnings can also be used for the reduction in place of more expensive very pure lanthanum metal. Extreme care should be taken to ensure that the reactants contain no calcium as it appears as an impurity in the final product if present in the charge. 

Eu—N system. — EuN was prepared [240] by direct combination of europium metal and nitrogen at 800° C. Keemm and Winkelmann s preparation [241] involved heating (700°) a mixture of finely divided europium and KC1 (1 3) in a stream of NH3. EuN, like SmN and YbN possesses the NaCl type structure. The lattice constant of EuN is a = 5.014 A according to Klemm and Winkelmann [241], and a = 5.007 0.004 A according to Eick et al [240]. However, the preparation of Eick et al. contained some impurity, possibly as oxide. 

Chemical isomer shifts for all four europium resonances have been measured in a number of compounds. The Eu values are given in Table 17 5. Comparison of pairs of values for two transitions should show a linear relationship. An early attempt to verify this for the Eu and Eu (97 and 103 keV) transitions in EU2O3, EUSO4, and Eu metal disclosed a large deviation [59], but this was later shown to be a result of impurity in the metal [62]. 

There are two ways to produce a pure radionuclide not contaminated with any other radioactivity. An extremely pure target can be used with a reaction path which is unique. Alternatively, the radioactive products can be purified after the end of the bombardment. For example, a 10 g sample of zinc irradiated for one week with 10 n cm s yields a sample of Zn (ti 244 d) with 7.1 X 10 Bq. If, however, the zinc target is contaminated with 0.1% of copper, in addition to the zinc activity, 3.0 x 10 Bq of Cu (ti 12.7 h) is formed. In another example element 102 believed to be discovered initially in a bombardment of a target of curium by carbon ions. The observed activity, however, was later found to be due to products formed due to the small amount of lead inq)urity in the target. Similarly, in neutron activation of samarium it must be very free of europium contamination because of the larger europium reaction cross-sections. Handbooks of activation analysis oftra contain information on the formation of interfering activities from impurities. 

The fluoride ion selective electrode is the most commonly used single crystal ISE. It is shown schematically in Fig. 15.9. The membrane is a single crystal of LaF3 doped with EuF2. The term doped means that a small amount of another substance (in this case, EUF2) has been added intentionally into the LaF3 crystal. (If the addition were not intentional, we would call the europium an impurity or contaminant ) Note that the two salts do not have the same stoichiometry. Addition of the europium fluoride creates fluoride ion vacancies in the lanthanum fluoride lattice. When exposed to a variable concentration of F ion outside the membrane, the fluoride ions in the crystal can migrate. Unlike the pH electrode, it is the F ions that actually move across the membrane and result in the electrode response. The F ISE is extremely selective for fluoride ion. The only ion... 

An anomaly shown as a peak at 16.1 K in the measurements of Lounasmaa (1966) (3.0-24.8 K) was later shown by Lounasmaa and Kalvius (1967) to be impurity induced, possibly due to europium hydride since hydrogen alone accounts for 3.2 atm% of the noimietallic impurities. A similar peak was not... 

The fluoride ISE is the most commonly used single-crystal ISE. It is shown schematically in Figure 15.9. The membrane is a single aystal of LaFj doped with EuFj. The term doped means that a small amount of another substance (in this case, EuFj) has been added intentionally into the LaFj crystal. (If the addition were not intentional, we would call the europium an impurity or contaminant )... 

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