Europium benzoylacetone

Lempicki and Samelson (160) in their first paper reporting laser oscillation in europium made use of europium benzoylacetonate (EuB3) dissolved in a mixture of ethyl and methyl alcohol. The ratio was 3 to 1 and the concentration of EuB3 was 5.2 x 1018 molecules/cm3. These solutions can be frozen into a glass uniformly at temperatures between —120° and — 170°C. In this range they report a fluorescent lifetime of about 5 x 10-4 sec. Additional information on laser action, fluorescent lifetimes, and spectral studies in chelates may be found in Ref. (138). 

The first reported laser action in rare earth complexes was obtained by Lempicki and Samelson [656] for europium benzoylacetonate in alcoholic solution. The laser parameters for this complex have also been evaluated by Lempicki and coworkers [656, 660] who found a slightly better quantum efficiency (0.8) for europium benzoylacetonate than for ruby (0.7), the solid state laser. The laser action of europium benzoylacetonate has also been investigated by Schimitschek [661] and Bhatjmik et al. [662]. Some other complexes of Eu3+ viz. dibenzoylmethide [665,664], m-4,4,4-trifluoro-l(2-thienyl)-l,3-butanedione [665], thenoyl-trifluoroacetonate [666, 667] were also found to lase. 

Similar examples for energy transfer from ligand localized levels to highly localized 4f levels are represented by the rare-earth chelates. Voloshin and Savutskii (1976) studied europium benzoylacetonate imder pressures up to 6 GPa. Exciting the triplet level they could observe the luminescence from the Eu " " ion. It was possible to describe the observed initial increase in the quantum yield of the Eu " " luminescence up to 2.5 GPa and the following decrease by the exchange resonance theory (Dexter, 1953). A more detailed study on different Tris chelates of Sm +, Eu +, Gd " ", and Tb " with -diketonates was performed by Hayes and Drickamer (1982), where the most dramatic effects of pressure on energy transfer phenomena were found for the Eu + chelates. 

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

Europium chelates derived from benzoylacetone (1-phenyl-l,3-butanedione) have been prepared by the reaction of europium (III) chloride with benzoylacetone in the presence of organic bases " and by the reaction between sodium benzoylacetonate and europium(III) chloride. t The procedure described here employs the reaction between europium(III) chloride and benzoylacetone in ethanol-... 

A solution is prepared which contains 5 X 10 mol of europium(III) chloride in 200 ml. of water. Since this chloride is quite hygroscopic, it is convenient to dilute a calculated volume of standardized ca. 0.5 M aqueous solution to 200 ml. Alternatively, 0.880 g. (2.5 X 10 mol) of europium (III) oxide is dissolved in a small excess of 6 M hydrochloric acid. The resultant solution is evaporated to a small volume to remove excess hydrochloric acid and ultimately diluted to 200 ml. To the solution of europium (III) chloride is added, with stirring, a solution of 4.0 g. (an excess) of benzoylacetone in 50 ml. of 95% ethanol. The resulting suspension is stirred with a magnetic stirring bar while 15 ml. of molar aqueous ammonia is added dropwise over a period of 2 hours. The mixture of product and excess benzoylacetone is filtered, washed with water, and dried in a vacuum desiccator to give approximately 4.4 g. of solid. 

Both the hydrated and anhydrous forms of the chelate give a red fluorescence (characteristic of the Eu " ion) when exposed to ultraviolet radiation. Fluorescence is also shown in solution. Interest in the fluorescence behavior of europium chelates is prompted by the use of these compounds in optical maser (laser) devices. Optical maser action has been demonstrated for europium chelates derived from benzoylacetone (though not for the tris chelate reported here ). 

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