Yb3 singly doped and Yb3 /Al3 co-doped high silica glass samples are prepared, and their luminescent properties are investigated. Al3 is considered as a beneficial activator for Yb3 -doped glass. However, the experimental result shows that the addition of Al3 results in the transformation from Yb3 to Yb2 and the improvement in the photon luminescence of Yb2 . These characteristics indicate the role of Al3 in Yb3 -doped glass.