RARE-EARTH CLUSTERING AND ALUMINUM CODOPING IN SOL-GEL SILICA - INVESTIGATION USING EUROPIUM(III) FLUORESCENCE SPECTROSCOPY

Eu3+ fluorescence spectroscopy is used to investigate the clustering of rare-earth ions and the effectiveness of aluminum codoping in dispersing and isolating rare-earth ions in sol-gel silica monoliths. Fluorescence line-narrowing (FLN) studies are demonstrated as a useful tool in identifying clustered and isolated Eu3+. Clustered Eu3+ is identified by the lack of a line-narrowing effect, which is attributed to energy transfer between adjacent Eu3+ ions. Clustering is shown to be significant, even in transparent samples with Eu3+ concentrations as low as 0.5 wt % Eu3+. Addition of Al3+ as a codopant has a profound impact on the bonding and structure of Eu3+ in silica. Significant fluorescence line narrowing is observed, which suggests that Al3+ codoping is effective in dispersing and isolating Eu3+ ions in the silica matrix. Fluorescence decay studies provide evidence of increased Eu3+ hydroxylation in the Al3+-containing samples.