Rare earth ion distribution in sol–gel silicate glasses

Sol–gel glasses are porous networks that have been densified through chemical processing and heat treatment. Due to their relative insolubility in silica, rare earth (RE) ions in silicate glasses enter as network modifiers and compete for non-bridging oxygens in order to complete their coordination. Energy transfer between Tb3+ ions is used here to study the distribution of RE ions in these porous glasses. The non-exponential decay of the 5D3 fluorescence is due to cross relaxation. Using a model for energy transfer in fractional dimensions and fitting the decay profile to a stretched exponential, the number of nearby Tb3+ ions and the dimensionality of the Tb3+ ions in the pores could be determined. Analysis indicates that the observed fluorescence originates from relatively isolated ions. Samples annealed below 950 °C exhibit a dimensionality of ∼1.2.