Interaction with rare-earth-exchanged

Considering the pH range 4—10 as the geochemical range, the redox potential due to the breakdown of water due to redox processes, the rare earths are predominantly present as Ln(III). Since the anions OH- and CO2 are present in natural environments, rare earths combine with these anions to form insoluble hydroxides and carbonates and hence immobilized. At lower pH, rare earth ions are adsorbed on clays, which are natural ion exchangers. The interactions of rare earth ions with humic and fulvic acids in soils, and Fe/Mn oxides are so strong, that they become immobile. 

The magnetic field at Eu + ions measured by the 103-keV resonance in rare-earth garnets doped with 2-5% Sm (M3FesOi2, M = Gd, Tb, Dy, Ho, Er, Eu, Tm, Yb, Lu, Y) increases by only 8% in that order [68]. Identical fields in YIG and LuIG in which the rare earth is diamagnetic show that the rare-earth-iron exchange interaction is insensitive to the lattice parameters which differ by 1%. However, in the series as a whole, the Eu - -/rare-earth exchange interaction does alter and the field shows a linear dependence with the spin moment of the host, = (gj — ). As already seen for the... 

In the nonradiative-resonance-exchange process an excited ion transfers its energy to a second ion without the emission of a photon, and with only a very minimal amount of energy lost to vibrations. For this process to occur, some coupling must, of course, exist between the ions. There is some evidence that this may be electrostatic (44,52). It appears that in most cases the ion-ion interaction is sufficiently weak that the energy levels of the rare earths are only slightly altered from their free ion positions. In this regard, one finds it convenient to talk about the system in terms of the states of the uncoupled ions. 

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