Europium , nonradiative processes

To test the above ideas, Weitz etal.(i2) performed experiments on the fluorescence decay from a thin layer of europium(III) thenoyltrifluoracetonate (ETA) deposited on a glass slide covered with Ag particles approximately 200 A in diameter. The fluorescence decay rate was found to increase by three orders of magnitude in comparison with that of ETA in solid form. In addition to the large increase in decay rate, there was also evidence for an increase in overall fluorescence quantum efficiency. It is not possible from Eq. (8.11) to say anything about the manner in which is partitioned between radiative and nonradiative processes, y should be written in terms of a radiative part yr and a nonradiative part ynr y = yr + y r. Since the radiative rate for dipole emission is given by... 

Windsor and his co-workers 10, 11) have shown, by direct excitation of the levels in a number of europium compounds, that the quantum yield of fluorescence decreases progressively as one successively excites Do, Di, and Do. While the yield on direct excitation of Do is quite dependent on the particular compound and medium (the value is 0.82 for the thenoyltrifluoroacetone chelate in acetone solution), the proportion of the energy lost between e.g. - Do and - Do within a given compound is rather insensitive to changes in the environment. These nonradiative processes from " D and Di, whose nature is not understood, would appear to be responsible for most of the ca. 40% energy loss in these materials. 

The direct electronic excitation of lanthanide ions is very inefficient because of their low absorption coefficients and the occurrence of nonradiative deactivation processes mediated by solvent molecules, particularly by water. Therefore, sensitizing ligands are applied. These sensitizers are often termed as anterma chromo-phores. By using antenna chromophores like acridone or diaiyl ketones, the excitation wavelength for europium complexes, which is usually <370 nm, can be shifted to the visible region [5-7]. 

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