Fluorescence Line-Narrowing Study of Eu³⁺-Doped Sol−Gel Silica:  Effect of Modifying Cations on the Clustering of Eu³⁺

Fluorescence line-narrowing spectroscopy is used to characterize the effect of metal cation codopants (Sr2+, La3+, Gd3+, Y3+, Lu3+, Sc3+, and Ga3+) on the state of aggregation of Eu3+ in sol−gel silica. Significant Eu3+ clustering occurs in samples doped only with Eu3+. The addition of codopants inhibits the clustering of Eu3+ and promotes better dispersion of Eu3+ in the glasses. The extent of the inhibition of clustering increases with field strength of the codopant and levels off at high field strength. The inhibition of clustering is correlated with the generation of strong crystal field bonding sites for Eu3+ in the presence of codopants. Characteristics of these sites include the presence of Eu−O−M (M = codopant) linkages and stronger interactions with the network-forming regions of the glass. Supporting luminescence decay and Raman spectroscopy measurements are also presented.