Fluorescence spectra of Eu3+ in synthetic polycrystalline anorthite; distribution of Eu (super 3+) in the structure

The localization of the trivalent rare-earth-element ions (REE³⁺) in synthetic polycrystalline anorthite is investigated by optical spectroscopy, using Eu³⁺ as a representative local probe. This ion is found either trapped in defects such as possibly twin and cleavage planes or substituted for Ca²⁺ in the structural sites. But the substitution of Eu³⁺ for Ca²⁺ is probably accompanied by deformation of the aluminosilicate framework, which results in the development of numerous additional sites that form three subsets, each related to an original site. Such a distribution may explain the low partition coeffcients of REEs between plagioclases and magmatic liquids and the fact that the REE partition coefficients are independent of atomic number.