Trivalent terbium

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is close to the stable empty, half-fUed, or completely fiUed sheUs. Thus samarium, europium, thuUum, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabili2ation of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

Nonradiative relaxations in solutions are particularly interesting. Terpi-lovskii (38) made a calculation of the probabilities of nonradiative transitions for the trivalent terbium ion in aqueous solution. He considered that the transitions were caused by Brownian movement of vibrations of the solvate envelope. 

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. 

It is convenient to divide the ions studied into four groupings, namely, terbium, europium, neodymium, and other trivalent ions. The reason for this grouping is that terbium, europium, and neodymium have been studied more extensively than the rest, and therefore the number of papers is larger. The greater attention paid to these trivalent ions is probably one of practical or potential practical applications to lasers. 

From the data of Hoogschagen and Gorter (104), the oscillator strength of the 5D4-+7F6 transition was obtained. By means of the Ladenburg formula, the spontaneous coefficient A46 was calculated. Using the relative-emission intensities, the rest of the A4J spontaneous-emission coefficients could be calculated. From these and a measured lifetime of 5.5 x 10 4 sec at 15°C, he calculated a quantum efficiency of 0.8 per cent. Kondrat eva concluded that the probability of radiationless transition for the trivalent terbium ion in aqueous solution is approximately two orders of magnitude greater than for the radiation transition. 

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. 

Axe and Weller (52) studied fluorescence and energy transfer of europium in yttrium oxide. In an experiment somewhat similar to that of Peterson and Bridenbaugh (54) on terbium, Axe and Weller were able to obtain experimental evidence for nonradiative-energy transfer between europium and other trivalent rare earth ions. Their study included both intensity and fluorescent-lifetime measurements. 

To a very large extent, most of the recent data on fluorescent decay times of the other trivalent ions (those beside terbium, neodymium, and europium) stems in some way from laser experiments. In this section some representative data on these are considered. 

Trivalent terbium with f8 configuration has energy levels similar to Eu3+ but in reverse order. The ground state is 7F6. The highest level and the lowest excited level (7F5) are separated from the ground state by 16000 cm and 2080 cm-1, respectively, and the... 

A comparison of XPS spectra of Tb207 and TbC>2 with those of Tb4C>7 in the 5p and 4d regions enables one to deduce the presence of both trivalent and tetravalent terbium in... 

The magnetic moment of trivalent gadolinium (Z = 64) complexes can be obtained by spin only formula but not for trivalent terbium complexes reason ... 

The series of 15 elements, lanthanium to lutetium, is known as the lanthanide series. These elements all form trivalent ions in solution quadrivalent oxidation states of cerium, praseodymium, and terbium, and bivalent states of samarium and europium are also obtained. 

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