Gd-incorporation and luminescence properties in sol–gel silica glasses

A thorough study was performed on Gd-doped sol–gel silica glasses, in the concentration range 0–8 mol% Gd. The analyses were carried out as a function of Gd content, before and after a post-densification thermal treatment. Different results concerning optical, vibrational, magnetic, and structural features were gathered in correlated experiments. The presence of Gd-rich nanoclusters was revealed. The size of nanoclusters increases by increasing the dopant concentration and by performing a rapid thermal treatment (RTT) at 1800 °C in air, which causes also a remarkable intensity increase of the 6P7/2 → 8S7/2 radioluminescence transition of Gd3+. Nanoclusters are amorphous, possibly close to a Gd2SiO5 stoichiometry as suggested by fast Fourier transform infrared spectroscopy (FTIR). FTIR studies revealed also the presence of Gd-dimers interacting with OH− groups. Moreover, the presence of isolated Gd3+ ions was detected by electron paramagnetic resonance investigations. Based on the results obtained with different techniques, the Gd-incorporation in silica glass host and the resulting optical properties are discussed.