Trivalent europium

Brix, Hiifner, Kienle, and Quitmann (4) carried out an interesting study on a series of compounds of divalent and trivalent europium using the 21.6-k.e.v., 8.8 nsec, level of europium-151 activated by a SmFs... 

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). 

The absorption and emission bands of Eu + ions show strong changes from one host crystal to another. For instance, Eu + ions emit in the violet region when incorporated into the Sr2P207 compound, while they emit in the green region in SrAl204 phosphor. This behavior is opposite to the practical insensitivity of the absorption and emission spectra of the trivalent europium ion to different host crystals. 

Trivalent europium is an excellent ionic probe for materials and its luminescence properties are extensively studied. Eu is one of the mostly informative elements in mineralogy, especially when the ratio Eu /Eu may be assessed. Both oxidation states are luminescent, but the hnes of Eu in minerals are usually very weak and concealed by other centers. By steady state liuninescence spectroscopy its luminescence has been confidently detected only in scheehte and anhydrite (Tarashchan 1978 Gorobets and Rogojine 2001). 

It has now become apparent that f-band superconductors can be understood in a normal way, like d-band ones" we have just to think about density of states, bandwidth lattice unstabilities and electron correlations to interpret it. This was clearly summarized by Smith after the discovery of superconductivity of Pa and Am. Superconductivity of Am is made by the J = 0 ground state of its six 5 f electrons as was stressed by Johansson , this could also be the case for stabilized trivalent europium metal. The importance of lattice instabilities (like in A-15 high Tc superconductors) was put forward by Fournier who showed that the very large 6T/8p slope for U was mainly due to a very targe change in the electron-phonon coupling associated with the low temperature phase transition. 

Van Uitert and Iida (55) suggested the applicability of the phonon-assisted-transfer mechanism to rare earth-rare earth energy exchange. They were able to correlate the emission intensity of the 5D0 level of trivalent europium or the5 D4 level of trivalent terbium with the closest, but definitely lower-lying, level observed for a second rare-earth ion. 

Crystal. Trivalent europium-doped compounds fluoresce a distinctive red color under ultraviolet excitation. This red emission, corresponding to the SD0->1F1 transition, often appears to the eye to be much weaker than the characteristic green emissions from terbium in the same hosts. This may be quite deceptive, since the human eye has very poor sensitivity to red in comparison to green. 

The fluorescence and stimulated emission from trivalent europium in yttrium oxide was studied by Chang (757). He obtained a value of 140 /zsec for the 5D state at liquid-nitrogen temperature, reducing to about 100 /zsec at room temperature. The lifetime of the 5D0 state was 870 /zsec, and was essentially the same at both room and liquid-nitrogen temperature. 

Glasses and Liquids. Gallagher and co-workers (152) examined in some detail the absorption, fluorescence spectra, and fluorescent lifetimes of trivalent europium in a variety of borate glasses. All data were taken at room temperature, and attempts were made to correlate the emission characteristics with various europium-glass interactions. The fluorescentlifetime measurements were made using a stroboscopic technique. 

As expected, tetravalent thorium is better extracted than trivalent europium. All calixarenes are stronger extractants than TOPO or OOCMPO. The dealkylated series is better than the alkylated one. For the dealkylated series and alkylated series, the sequence of increasing efficiency toward two cations is tetramer < octamer < hexamer. 

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... 

X-ray photoelectron spectrum of EuCu2Si2 along with the calculated spectrum for the compound are shown in Fig. 9.26. The spectrum clearly shows the presence of both divalent and trivalent europium in the alloy. The spectrum of YCu2Si2 is also included in Fig. 9.26... 

Akins et al. successfully immobilized polyoxometaloeuropates [(Eu2PWio038)4(W30s (H20)2(0H)4)] inside the channels of MCM-41 mesoporous molecular sieve material by means of the incipient wetness method. For proper host-guest interactions, amine groups were introduced into the system as a result of an aminosilylation procedure. The photoluminescent behavior of the composite at room temperature indicates a characteristic trivalent europium emission pattern corresponding to Dq transitions. Such a composite might represent a new material with potential applications as a photoluminescent device or phosphor [85]. 

Generally, TL spectra of diketonate complexes are characterized by the metal ion-centered transitions, which exhibit similar position and spectral profiles as those photolu-minescent ones ". The TL spectra of trivalent europium diketonates usually display only those intraconfigurational F] (J = 0-4) transitions which are dominated by the... 

Lee CJ, Wang SS, and Wang SG. Extraction of trivalent europium via emulsion liquid membrane containing PC-88A as mobile carrier. 

Fig. 4. The excitation and the luminescence spectrum of the uranyl ion in phosphate glass compared with positions of J-levels in trivalent europium and samarium (taken from Fig. 3)...

The modeling with Eq. (81) is trivial (Eqs. (85) and (86)) except for the calculation of the statistical factors. Originally, the trivalent europium atoms were considered as free cations with R3 symmetry and Eu,Li3f 2 Eu,Li3f (piguj-g 78A). A fit of the model (Eqs. (85)... 

Trivalent europium has been demonstrated to produce a bright red fluorescence, which peaks at about 615 nm in glasses. More recently, europium was successfully incorporated into gel-derived glasses [33,34]. Possible applications include solid-state lasers in the visible and fiber-optic amplifiers. The fluorescence spectra of Eu3+-doped silica is presented in Fig. 5. The 615 nm peak associated with the 5Do transition state is clearly evident, along with three... 

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