Energy transfer between ions

Energy transfer between ions in a solid can be accomplished either radiatively or nonradiatively. Only the nonradiative processes will be discussed in this review. Radiative transfer which is the trivial case of absorption by the acceptor of the light emitted by the donor can be easily treated by measuring the absorption and emission characteristics of the ions involved and correcting for the experimental geometry. 

More related to general photochemistry are the papers which have appeared on wholly or partly diffusion-controlled reactions. The effect of a very short lifetime of the donor on the calculation of fluorescence quantum yields and lifetimes has been analysed by Viriot et al. Andre et al. analyse the kinetics of energy transfer to an acceptor when there are two different excited states capable of acting as donors and when interaction between these states is possible. The exchange interaction contribution to energy transfer between ions in the rapid diffusion limit... 

For efficient luminescence of Ln, the inter-ionic nonradiative rate is decreased by diluting the ion into a transparent host lattice. Thus, fast migration between ions, for which the excitation finally ends up at defect or killer sites, and energy transfer between ions [24] are both minimized. 

Miyakawa T, Dexter DL (1970) Phonon sidebands, multiphonon relaxation of excited states, and phonon-assisted energy transfer between ions in solids. Phys Rev B 1 2961... 

This condition means that there should be less than one atom per one wavelength volume. In a solid diis is never the case. Fortunately we know that dipole-dipole energy transfers between ions in the absence of clusters are important only when they are separated by less than about 20 A in the case of trivalent R ions with oscillator strength f w 10. For a stronger transition, this distance may be enlaiged. It means that higher concentrations are possible in solids and consequendy the sample may have smaller dimensions than for experiments in gases. 

The matrix element (36.52) gives rise to two-body energy transfer between ions 1 and 2. 

The surface work fiincdon is fonnally defined as the minimum energy needed m order to remove an electron from a solid. It is often described as being the difference in energy between the Fenni level and the vacuum level of a solid. The work ftmction is a sensitive measure of the surface electronic structure, and can be measured in a number of ways, as described in section B 1.26.4. Many processes, such as catalytic surface reactions or resonant charge transfer between ions and surfaces, are critically dependent on the work ftmction. 

Energy transfer between organic molecules and transition metal ions. V. L. Ermolaev, E. G. Svesh-nikova and T. A. Shakhveraov, Russ. Chem. Rev. (Engl. Transl.), 1975,44,26-40 (110). 

The above nonstatistical view of reaction (2) has been reinforced by recent experiments made under LP conditions and presents a great challenge to the GPIC community. It now appears that the LP rate constants obtained for any nonstatistical reaction of this type will be extremely difficult to interpret in terms of candidate mechanisms and potential energy surfaces envisioned for that reaction. An accurate prediction of for such reactions would have to include a set of very complex factors, some of which are not presently well understood. These factors would include the initial distributions of energy within the set of collision complexes, X, formed under all possible collision impact conditions the rates of energy transfer between all vibrational modes within the species, X and Y and the mode-dependent rate constants for the motion of individual species within the sets of ion complexes, X and Y, in both directions on the reaction coordinate. 

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. 

Ce in the presence of Yb and of U in the presence of Nd. These changes can be ascribed to radiationless-energy transfer between the ions. There are also some additional smaller variations in decay times, such as the decrease of the Yb mean life in the presence of U. These are probably associated with alterations in the crystalline field caused by the multiple doping. 

Finally, the interaction between the dipole and quadrupole of donor and acceptor molecules [13] is generally much weaker than the dipole-dipole interaction. The dipole—quadrupole term [/ (r) r-8] is typically 10—100 times weaker than the dipole—dipole term, though if the acceptor absorption spectrum is symmetry-forbidden (and so weak) but not spin-forbidden, the dipole transition moment for the acceptor is small [127]. Such is the case for energy transfer between rare-earth ions in tungstates typically separated by 1.7 nm [146]. The kinetics of dipole—quadrupole energy transfer are discussed in Chap. 4, Sect. 2.6. 

The optical studies performed on most samples of table 1 were aimed at different aspects of the f-electron properties. A considerable amount of the work was concerned with the energy level shifts under pressure. From these shifts, variations of free-ion parameters, crystal-field parameters or crystal-field strengths with pressure have been deduced. Other studies concentrated on changes in lifetimes or intensities, the efficiency of energy transfer between rare earths or rare earths and other impurities or on electron-phonon coupling effects under pressure. The various aspects investigated under high pressure will be presented within the next sections. 

Fig. 20. Energy back-transfer model describing the energy transfer between the semiconductor host and the lanthanide ion R3+ (Culp et al., 1997 Takarabe et al., 1995).

At the end of the 1950 s, Crosby and Kasha reported the rather exceptional case of near-infrared luminescence of trivalent ytterbium ion in an 1 3 (Ln L) chelate occurring after intramolecular energy transfer between the organic ligand, in this case dbm (48b), and the lan-... 

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