Silicon implanted and annealed SiO2 layers are studied usin g photoluminescence (PL) and positron annihilation spectroscopy (PAS). Two PL emission bands are observed. a band centered at 560 nm is present in as-implanted samples and it is still observed after 1000 degrees C annealing. The emission time is fast. A second band centered at 780 nm is detected after 1000 degrees C annealing. The intensity of the 780 nm band further increased when hydrogen annealing was performed. The emission time is long (1 mu s to 0.2 ms). PAS results show that defects produced by implantation anneal at 600 degrees C. Based on the annealing behavior and on the emission times, the origin of the two bands is discussed.