Figure 6.

Optical absorption spectra of a dense silica glass doped with silver. Before hydrogenation (a), after hydrogenation (b), after hydrogenation and annealing at 300°C (c), 500°C (d), 700°C (e), 900°C (f), 1,100°C (g) and 1,200°C (h) for 1 h and 30 min. Inset: photograph image of the sample heated under air condition at 500°C for 1 h and 30 min.