Raman and luminescence study of Tb3+ doped monolithic silica xerogels

Monolithic silica xerogels were doped with Tb3+ concentrations ranging from 200 to 40000 ppm. Structural differences, such as the degree of densification or the different OH-contents were quantified by Raman spectroscopy. The Tb3+ luminescence properties were studied as a function of the temperature of heat-treatment, the time of heat-treatment, and the Tb3+ concentration. Samples densified at 900°C or above and with a Tb3+ content lower than 20000 ppm show emission from both the 5D3 and the 5D4 state. Emission spectra and decay curves indicate that Tb3+ ions have a strong tendency to form clusters also at a very low Tb3+ concentration. This clustering results in a very efficient quenching of the 5D3 emission due to energy transfer processes among Tb3+ ions. Moreover, the luminescence of the 5D3 state is quenched by non-radiative transitions induced by OH vibrations. © 1998 Elsevier Science B.V. All rights reserved.