THE DOUBLE NATURE OF THE 3.1 EV EMISSION IN SILICA AND IN GE-DOPED SILICA

The 3.1 eV photoluminescence emission ('beta' band) has been studied both in natural silica and in Ge-doped silica in the temperature range 80-475 K under UV and VUV excitation. A detailed analysis of the beta band, as a function of temperature and excitation energy in the 5 eV region, gives evidence for a double structure of this emission. A first component peaks at 3.05 eV at 300 K and increases its intensity as the temperature rises up to 380 K. A second one has a peak at 3.21 eV at room temperature and its emission intensity is constant up to 300 K. The two beta bands may be due to two different modifications of a Ge-related centre. However the presence of the beta emission in silica obtained from fused quartz with low Ge content would indicate that other impurities could favour the presence of the beta band as well.