Europium oxalate

The decomposition of europium oxalate [82] occurred at a significantly lower temperature (520 K). Results were interpreted as indicating cation reduction to the divalent state. In vacuum, the products of decomposition were europium(II) carbonate and finely-divided carbon. In carbon dioxide at 593 K, europium(II) oxalate is stabilized. In an oxidizing atmosphere, europium is reoxidised and EU2O3 is formed at 663 K. A reaction mechanism was proposed in which carbon monoxide reacted with the oxalate ion to form carbon dioxide and 203. The reactions of ytterbium oxalate were similar. 

With a view to overcoming such experimental difficulties, we have developed a promising technique — conversion electron MHssbauer spectroscopy(GEMS) and depth-resolved conversion electron MfJssbauer spectroscopy(DCEMS) — for monitoring photochemical reactions in the surfaces of inorganic solids (iron and europium oxalates). 

EuSe is formed in the in situ reaction of EUCI3 (from a matrix dehydration procedure) with dry H2Se in a vitreous carbon boat at ca. 1025 K in 2 h. The product is cooled under a stream of H2Se-h He and subsequently outgassed at ca. 1075 Kat 10" Torrto remove adsorbed H2Se and Se. The dark khaki colored EuSe sample appeared insensitive to the laboratory atmosphere, Hariharan, Eick [12]. EuSe from the reaction of EUSO4 with H2Se is often contaminated by EuS, Pink [13]. The compound is obtained by reduction of europium oxalate at 800 to 900°C ... 

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 a—time curves for the vacuum decomposition at 593—693 K of lanthanum oxalate [1098] are sigmoid. Following a short induction period (E = 164 kJ mole-1), the inflexion point occurred at a 0.15 and the Prout—Tompkins equation [eqn. (9)] was applied (E = 133 kJ mole-1). Young [29] has suggested, however, that a more appropriate analysis is that exponential behaviour [eqn. (8)] is followed by obedience to the contracting volume equation [eqn. (7), n = 3]. Similar kinetic characteristics were found [1098] for several other lanthanide oxalates and the sequence of relative stabilities established was Gd > Sm > Nd > La > Pr > Ce. The behaviour of europium(III) oxalate [1100] is exceptional in that Eu3+ is readily reduced... 

Am3+ is the most stable oxidation state of the metal. In trivalent state, its properties are simdar to europium. Am3+ reacts with soluble fluoride, hydroxide, phosphate, oxalate, iodate and sulfate of many metals forming precipitates of these anions e.g., Am(OH)3, Am(103)3, etc. 

Oxides. Industrially, the most important of this group is Y203 Eu3 +. The preparation is generally carried out by precipitating mixed oxalates from purified solutions of yttrium and europium nitrates. Firing the dried oxalates at ca. 600 °C is followed by crystallization firing at 1400-1500 °C for several hours [5.382],... 

Europium (II) acetate, formation of, from europium amalgam, 2 68 Europium(III) acetate, 2 66 citrate solution of, 2 67 Europium amalgams, 2 65, 66, 68n. Europium (II) carbonate, 2 69, 71 Europium(II) chloride, 2 69, 71 formation of, from europium amalgam, 2 68 Europium (III) oxalate, 2 66 Europium (III) oxide, 2 66 Europium (II) salts, 2 69 Europium(II) sulfate, 2 69, 70... 

In general, lanthanides can be separated from mixtures with other elements by precipitation as oxalates or fluorides. Cerium and europium can conveniently be removed from the others, the former by oxidation to CeIV and precipitation as the iodate, and the latter by reduction to Eu2+, which can be precipitated as EuS04. 

The zinc reduction of Eu + to Eu +, followed by its precipitation as the sulfate, is a traditional step in the separation of europium from other lanthanides. In general, the solubilities of the inorganic compounds of the Ln + ions resemble those of the corresponding compounds of the alkaline earth metals (insoluble sulfate, carbonate, hydroxide, oxalate). Both europium and the Sm + and Yb + ions can also be prepared by other methods (e.g. electrolysis), although these solutions of the latter two metals tend to be short-lived and oxygen-sensitive in particular. Eu + is the only divalent aqua ion with any real stability in solution. Several divalent lanthanides can, however, be stabilized by the use of nonaqueous solvents such as HMPA and THE, in which they have characteristic colors, quite distinct from those for the isoelectronic trivalent ions on account of the decreased term separations. 

The same effect can be observed if the stage of spin-on deposition of sol is replaced by immersion of the sample in solution of europium salt. These examinations show that porous anodic alumina grown in oxalic acid which displays inherent blue PL can be used for fabrication of dichromatic luminescent images only, while red luminescence related to Eu is not observed from the same area of the sample. 

Figure 3. PL spectra measured from dichromatic luminescent image (a) blue area of porous anodic alumina film of 30 pm thickness after anodizing in oxalic acid electrolyte (b) red area of a porous anodic alumina film of 20 pm thickness after anodizing in orthophosphoric acid electrolyte, followed by immersion in europium nitrate and subsequent heat treatment at 200 °C for 30 min.

Europium and PAA luminescences from the second group of specimens, subjected to sequential anodizing in two electrolytes (Fig. Ig) were excited efficiently with 337 nm light (Fig. 3). The PL spectrum measured from the area of aluminium films anodized initially in oxalic acid electrolyte into open windows (Fig. ld,e) reveals mainly strong blue luminescence band of PAA (Fig. 3a). Significantly, red emission from this area of the sample is not observed. At the same time, the PL spectrum measured from the area of... 

Assume AH => 0 (similar to oxalate complexation, and carbonate complexation of europium). Estimated from Smith and Martell (1976), 1 M, 20-25 C. 

We have also studied the photolysis of europium(III) oxalate by means of the conversion electron MOssbauer and ESR technique... 

The lutetium hahdes (except the fluoride), together with the nitrates, perchlorates, and acetates, are soluble in water. The hydroxide oxide, carbonate, oxalate, and phosphate compotmds are insoluble. Lutetium compounds are all colorless in the solid state and in solution. Due to its closed electronic configuration (4f " ), lutetium has no absorption bands and does not emit radiation. For these reasons it does not have any magnetic or optical importance, see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Neodymium Praseodymium Promethium Samarium Terbium Ytterbium. 

The lanthanides are separated from most other elements by precipitation of oxalates or fluorides from nitric acid solution. The elements are separated from each other by ion-exchange, which is carried out commercially on a large scale. Cerium and europium are normally first removed, the former by oxidation to Celv and removal by precipitation of the iodate which is insoluble in 6M HN03 or by solvent extraction, and the latter by reduction to Eu2+ and removal by precipitation as insoluble EuS04. 

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