Er-doped silicon-rich SiO2 thin films were prepared by an rf co-sputtering method, followed by thermal annealing at 700-1200℃ for 30min. The microstructure is studied by transmission electron microscopy (TEM) and xray diffraction (XRD). When the films are annealed at T ＞ 900℃ , silicon nanocrystals (nc-Si) enveloped by amorphous silicon (α-Si) can be observed. The thermal quenching behaviour at λ = 1.535 μm and its relation with the annealing temperature are also investigated. With the increasing annealing temperature, the portion of α-Si and the intensity quenching both decrease. Efficient luminescence from Er ions and weak intensity thermal quenching can be obtained from the sample annealed at 1100℃ . The role of α-Si in the non-radiative processes at T ＞ 100 K is discussed.