HYDRATED RARE-EARTH-METAL ION-EXCHANGED-ZEOLITE A - CHARACTERIZATION BY LUMINESCENCE SPECTROSCOPY .1. THE GD-3+ ION

The luminescence properties under high-resolution excitation and emission conditions at 4.2 K of hydrated Gd3+ ion-exchanged zeolite A are reported. From these luminescence measurements it is found that in a sample containing 0.8 wt.% Gd3+, only one site appears to be occupied by Gd3+. In a freshly prepared sample containing 5 wt.% Gd3+ one site inside the zeolite is occupied by Gd3+. Other Gd3+ ions appear on silica surfaces present in the sample. When measurements on this sample were repeated a few months after preparation, Gd3+ ions were found in three sites within the zeolite cages. Information on the surroundings of the Gd3+ ions in the different sites was obtained from the emission spectra. In this way the possibility of characterizing the coordination of rare-earth-metal ions in zeolites by luminescence spectroscopy was evaluated.