Terbium compounds

Rieke and Allison (97) studied the fluorescent lifetime of terbium in the chelate terbium trianthranilate (TbAn3). They concluded that the spectra and fluorescent lifetime of the chelate differ markedly from unchelated terbium compounds. Fluorescent-lifetime measurements were made at 25°C, 0°C, and 77°K using a stroboscopic light source with a decay time of 20 /xsec and a comparison was made with TbCl3 4H20. At all... 

Another example of a different type of correlation of structural to photophysical properties is shown in a study of a unique terbium compound [63]. This compound will be briefly discussed and is depicted in Figure 7.9 with its nonlinear emission properties with excitation at 800 nm. The photophysical properties are atypical and rather extraordinary due to the unusual molecular structure of the co-crystallization compound (4) of the organic chromophore and the terbium salt This compound shows both multiphoton absorption induced green f-f emission from the terbium ion as well as second-harmonic generation. However, unlike previously... 

The berkelium monopnictides have been prepared on the multimicrogram scale by direct combination of the elements (138). In all cases, the lattice constants of the NaCl-type cubic structures were smaller than those of the corresponding curium monopnictides but comparable to those of the corresponding terbium compounds. This supports the semimetallic classification for these compounds. One additional report of BkN has appeared (139). The lattice parameter derived from the sample exhibiting a single phase was 0.5010 0.0004 nm, whereas that extracted from the mixed-phase sample of BkN resulting from incomplete conversion of a hydride was 0.4948 0.0003 nm. Clearly, additional samples of BkN should be prepared to establish more firmly its lattice constant. 

In absorption spectra, the probability of a transition is expressed by its oscillator strength, /. While / is close to unity for allowed transitions, it is of the order of 10 -10 and 10 -10 respectively for spin-allowed transitions within the 3d and 4f configurations. Efficient conversion of a UV radiation to light (as needed in fluorescent lamps) requires strong absorption properties at the wavelength of incident photons. Figure 1 shows a comparison of the luminescence intensity for 4f- 5d (A/ = 1) and 4f- 4f (A/ = 0) excitations in the case of a terbium compound. 

The only tetrahalides isolated are the fluorides of Ce, Pr, and Tb. Only Cep4 is made by direct fluorination of the metal (as well as CeXs (X = Cl, F)) the terbium compound is made by fluorination of TbFs while the more unstable PrF4 is made by the reaction of Na2PrFe with dry HF (it decomposes around 70 °C). CeCLi, expected to be the most stable tetrachloride, has never been isolated (though Lewis base adducts have, cf. PuCL,). 

Dysprosium pertechnate and its hydrates have been ascribed the same structures as the corresponding terbium compounds. 

For most lanthanides, the 3+ oxidation state is the most stable, and therefore almost all REE-oxides are presented as REE2O3. However, some of the lanthanides may have several valences in one and the same oxide, so formulas are given to express this phenomenon. Praseodymium oxide usually contains 3+ and 4+ praseodymium in a somewhat variable ratio, depending upon the conditions of formation. Its formula is rendered as PreOn. Similarly, Xb407, one of the main commercial terbium compounds, contains some Xb4+ along with the more stable Xb3+. Ce has the 3+ state as most stable oxidation state, and the oxide is represented as 6203. 

Thus, Mosander s activities led to the originally two-element division into a six-element division. The cerium compounds are yellow at the higher oxidation level and colourless at the lower oxidation level, lanthanum compounds are white, didymium compounds are red, yttrium and erbium compounds are white, terbium compounds are pink. Chemists existed, of course, who disputed the existence of these elements. Unequivocal identification of elements was, however, possible in later times only. In the period in question, the main characteristics on the basis of which a substance could be qualified as a new element were separability, colour, crystal shape and reactivity. Even atomic mass determinations were largely uncertain, particularly in the group of the rare earth elements, it will be seen in the... 

In the perovskites BaCeOg and BaPrOg, the Ba + ion has eight Ba-O distances between 2.67 and 3.17 A, with three more at 3.60A. The terbium compound BaTbOa, which adopts a different crystal structure, has three Ba-O distances of 2.807 A, six at 3.031, and three at 3.264 A, and is thus nearer the twelve co-ordination valid for close-packed systems. 

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