Decomposition and first stages of the crystallization in fluorozirconate glasses. Study by the 1D2 -> 3H4 emission of the Pr3+ ions

The effect of heat treatment on the structure of different fluorozirconate glasses, and the first stages of crystallization have been studied by the observation of the 1D2 -> 3H4 emission of incorporated Pr3+ ions. It is shown that the non-exponential decays governed by the quenching of the fluorescence by cross-relaxation are very well fitted by the Inokuti-Hirayama model in the non-heated glasses, and by the Klafter-Blumen model for a fractal distribution of luminescent ions in glasses heated at Tg or at temperatures slightly higher. The change of the ion distribution reflects the modification of the glass structure by spinodal decomposition. Two different types of microcrystals were found by the observation of the fluorescence, corresponding to two different sites in glass. But, due to the spinodal decomposition, it was impossible to obtain transparent vitroceramics.