Structural study of the Eu3+ environments in fluorozirconate glasses: role of the temperature-induced and the pressure-induced phase transition processes in the development of a rare earth's local structure model.

ABSTRACT

The correlation between the optical properties of the Eu(3+) ions and their local structures in fluorozirconate glasses and glass-ceramics have been analyzed by means of steady-state and time-resolved site-selective laser spectroscopies. Changes in the crystal-field interaction, ranging from weak to medium strength values, are observed monitoring the luminescence and the lifetime of the Eu(3+) ions in different local environments in the glass. As key roles in this study, the Eu(3+) luminescence in the thermally-induced crystallization of the glass and the pressure-induced amorphization of the crystalline phase of the glass-ceramic experimentally states the existence of a parent local structure for the Eu(3+) ions in the glass, identified as the EuZrF(7) crystalline phase. Starting from the ab initio single overlap model, crystal-field calculations have been performed in the glass and the glass-ceramic. From the site-selective measurements, the crystal-field parameters sets are obtained, giving a suitable simulation of the (7)F(J) (J=0-6) Stark energy level diagram for the Eu(3+) ions in the different environments present in the fluorozirconate glass. A simple geometrical model based on a continuous distortion of the parent structure is proposed for the distribution of local environments of the Eu(3+) ions in the fluorozirconate glass.