Post annealing immersion: A new technique for studying rare earth ions in porous materials

A novel technique is introduced for studying how rare earth ions are incorporated into the matrix of porous materials. Tb3+-doped silica sol–gel is annealed to form porous glass and immersed in an aqueous Gd(NO3)3 solution. Re-heating removes the liquid and deposits Gd3+ ions on the internal pore surfaces. Spectroscopic investigation of Gd3+→Tb3+ energy transfer yields information about the location of Tb3+ dopant ions relative to pore surfaces. Results from post-annealing immersion experiments indicate that most Tb3+ dopant ions are close to pore surfaces when sol–gel glass is annealed to 700 °C. The observed energy transfer decreases with higher annealing temperatures, indicating that Tb3+ dopants in densified regions are isolated from Gd3+ ions deposited on pore surfaces. Al3+ co-doping affects both the overall sample density and the degree of Gd3+→Tb3+ interaction in post-annealing immersion samples.