Abstract The optical properties of Yb-doped sol–gel silica glasses were studied by optical absorption and radio-luminescence (RL) measurements, that revealed the typical absorption and emission pattern of Yb 3+ ions. Moreover, RL bands in the 1.5–3.5 eV interval were also observed, and related to defects of the silica matrix. The RL intensity temperature dependence, investigated in the 10–320 K interval, evidenced the presence of the SiO 2 self-trapped exciton emission at 2.2 eV, whose intensity was rapidly quenched by temperature increasing. At variance, the Yb 3+ emission intensity increased markedly by temperature increasing. This phenomenon is interpreted by considering a competitive role of point defects in free carrier trapping, evidenced by parallel wavelength resolved thermally stimulated luminescence measurements.