Luminescence properties of rare-earth ions in SiO2 glasses prepared by the sol–gel method

Radio-luminescence (RL) and wavelength resolved thermally stimulated luminescence (TSL) measurements have been performed on sol–gel SiO2 glasses, undoped (with high OH- or low OH-content) and rare-earth (Ce, Gd and Tb) doped in the temperature range 10–310 K. Moreover, a comparison has been performed between undoped sol–gel and commercial glasses. In undoped samples RL spectra are characterized by emissions at 1.9 eV, 2.4 eV (only in high OH-content glasses) and 2.7 eV at 10 K; their nature is discussed and related to different intrinsic defects. Strong emission quenching is observed by temperature increasing. Besides similar intrinsic bands, the doped glasses RL emission spectra display typical emissions related to 5d–4f (Ce3+), 6P–8S (Gd3+) and 5D3–7Fj, 5D4–7Fj (Tb3+) transitions respectively, whose amplitudes increase by increasing the temperature above 150 K. TSL measurements show the existence of glow peaks at ≈100 K and 220 K. The observed increase of RL rare-earth emission amplitudes above 150 K can be explained by considering (i) the progressive decrease of competitive host matrix recombination channels and (ii) the free carriers trapping at defect sites during irradiation (monitored by TSL), whose stability strongly depends upon temperature.