VIBRATIONAL SPECTROSCOPY OF OH-DEFECTS IN SOL-GEL Ce3+ AND Gd3+-DOPED SILICATE GLASSES

Vibrational modes of OH, as stretching, bending, combination, and overtones, were monitored by means of FTIR spectroscopy in Ce³⁺- and Gd³⁺-doped silicate glasses, prepared by means of the sol-gel technique, submitted to different thermal treatments, and aimed to applications as scintillators. The dopant concentration was varied in a wide range (10⁻³-8% m.f.) and co-doped samples were also investigated. In this framework, the effects of OH and of rare-earth (RE) clustering, i.e. two possible non-radiative decay channels, on the IR spectra in the 500-14 000 cm⁻¹ were examined. OH was detected as belonging either to water and to silanol in samples densified at 450 and 750 °C, while in those treated at 1050 °C only Si-OH groups were present in a concentration of the order of 1% m.f., nearly regardless of the RE amount. An absorption peaking at 4250 cm⁻¹ was identified as related to an OH combination mode (bending+stretching) perturbed by a Gd cluster on the basis of its amplitude dependence on the Gd concentration and rapid thermal treatment.