Mo¨ssbauer effect studies of coordination and oxidation-reduction properties of Eu ions in zeolites

Abstract

Zeolites exchanged with Eu 3+ ions were prepared based on three kinds of zeolite hosts: A zeolite, X zeolite, and Y zeolite. The 152Eu Mo¨ssbauer effect was used to study the coordination properties of Eu 3+ ions in these zeolites. The results showed that EU 3+ ions occupy two sites where the electric-field gradient tensors are axially symmetric. The isomer shift and quadrupole splitting of Mo¨ssbauer spectra of Eu depend on the electronegativity of the zeolite hosts. With moderate conditions (less than 720°C), the Eu 3+ ions in the three kinds of zeolites were reproduced to Eu 2+ ions. The coordination property and the stability of the Eu 2+ were also studied with 151Eu Mo¨ssbauer effect spectroscopy. The results indicated that the symmetry of the electric-field gradient at the Eu site is lowered.