Cathodoluminescence and IR absorption of oxygen deficient silica - influence of hydrogen treatment

The cathodoluminescence (CL) and IR absorption of silica samples with normal stoichiometry as well as with an extremely high level of oxygen deficit were studied. Additionally, some samples have been treated in hydrogen at 800°C. Crystalline quartz was used for reference measurements and the CL data have been compared with those of X-ray excited luminescence (XL). The luminescence spectra of silica have a band at 1.85 eV due to non-bridging oxygens and the two bands at 2.7 and 4.4 eV due to two-fold-coordinated silicons. The energetic yield for CL is about 0.1%, for XL it approaches 0.15%. Cathodoluminescence of quartz at temperatures > 130 K exhibits the self-trapped exciton luminescence. Under electron beam irradiation there is a production and destruction of luminescence centers, whereas X-ray excitation mainly leads to electron-hole recombinations on existing centers. After hydrogen treatment the IR spectra contain bands due to Si-H and Si-O-H, independent of the oxygen deficiency. The hydrogen treatment affects the cathodoluminescence properties of oxygen deficient silica by modifying the luminescence centers themselves.