Transitions terbium

Flumequine is shown to form a complex compound with terbium(III), whose fluorescence spectmm has one band with a maximum at 545 nm (emission of terbium(III)), it corresponds to the transition. The... 

A broad range of metal centers have been used for the complexation of functional ligands, including beryllium [37], zinc, transition metals such as iridium [38], and the lanthanide metals introduced by Kido [39], especially europium and terbium. Common ligands are phenanthroline (phen), bathophenanthrolin (bath), 2-phenylpyridine (ppy), acetylacetonate (acac), dibenzoylmethanate (dbm), and 11 thenoyltrifluoroacetonate (TTFA). A frequently used complex is the volatile Eu(TTFA)3(phen), 66 [40]. 

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. 

A comparison of the decay times of the 5D4-+7F5 transitions for terbium chloride at room temperature are as follows ... 

It is interesting to note that the emission spectra of the terbium chlorides solvated with H20 and D20 show no discernible differences. Since the rare-earth chlorides solvated with D20 are isostructural with the chlorides solvated with H20 and since the emission spectra are essentially identical, Freeman et al believe that the variations in lifetime are not brought about by changes in the radiative-transition probabilities, but are a consequence only of changes in radiationless quenching efficiencies. They speculate that the decreased efficiency upon substitution of D20 for H20 must be related to the large changes in vibrational frequencies associated with substitution of the H atoms by the D atoms. 

The authors point out that the fluorescent lifetime of the terbium chelate at 25°C is more than twice that of the chloride and that measurements at 0°C and 77°K showed that the lifetime for TbAn3 increases slightly as the temperature decreases. They also measured the lifetimes of each of the individual 5Z)4->7/ transitions and found the same values, as expected. 

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. 

They measured the decay times of three of the possible seven terbium transitions from the 5D4 state to the ground-state multiplets and found them to be the same at room temperature, and to have the same temperature dependence. This result is not surprising, since all the emissions originate from the same state. 

The authors believe that the decreases in decay times are associated primarily with changes in quantum yield. This may be inferred from the fact that both the emission intensities and lifetimes are falling off at about the same rate with temperature. One thus concludes that the luminescence of sulfuric acid solutions of terbium sulfate is subjected to much greater temperature quenching than the luminescence in aqueous solution of the same salt. The increasing probability of radiationless transitions is undoubtedly connected in some manner with greater interaction of the radiating ion with the solvent molecules. 

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. 

In YV04 Eu3 +, the europium emission lines at 619 and 614 nm, due to the transition 5D0 - 1D0, are not quenched up to 300°C. Although quenching occurs at higher temperatures, the main lines still retain 50% of their intensity at 500 °C. Small quantities of terbium activate the red Eu3+ lines at higher temperatures [5.394],... 

These results indicate that the antiferromagnetic transition in TbB44Si2 is actually of dimer-like nature, where non-magnetic substitution leads to broken pairs resulting in free spins (Mori, 2004). The antiferromagnetically coupled pairs do not feel the effects of dilution of other terbium sites, and therefore, are stable below Hq which is a unique value regardless of the doping content. 

The lanthanides, unlike the transition metals and the actinides, tend not to form compounds over a range of oxidation states. The +3 oxidation state is characteristic of all of the lanthanides, and the oxide fluorides of formula LnOF (Ln = lanthanide metal) are well known. The less stable oxidation states of + 2 and + 4 are known, but the latter is represented only by the dioxides and tetrafluorides of cerium, praseodymium, and terbium, and no tetravalent oxide fluorides have been reported. 

---