Terbium(III) doped silica-xerogels: effect of aluminium(III) co-doping

Abstract

Monolithic silica xerogels doped with different concentrations of Tb 3+ and Al 3+ ( xTbO 1.5– x6AlO 1.5–SiO 2, x=2 × 10 −4, 4 × 10 −4, 5 × 10 −3) were prepared by a sol–gel route: Mixtures of tetra-methoxy-silane, Tb(NO 3) 3 · 5H 2O, Al(NO 3) 3 · 9H 2O, ethanol, and water were condensed at 60°C using HNO 3 as catalyst. The samples were sintered at 950°C for 86 h in air. The Raman spectra indicate several structural differences among the samples and show that there is a compositional dependence of the gel glass transformation temperature. The sample with x=5 × 10 −3 is glasslike on the outer part showing onset of crystallisation in the inner part of the sample. The samples with smallest dopant concentrations ( x=2 × 10 −4, 4 × 10 −4) contain pores. All samples luminesce from the 5D 4 and 5D 3 states of Tb 3+ with excitation at 355 nm. The 5D 3 luminescence increases with respect to the 5D 4 luminescence with increasing dopant concentration, indicating that the larger Al 3+ concentrations are effective in dispersing Tb 3+ ions. This result is also confirmed by the analysis of the decay of the 5D 3 and 5D 4 luminescence.