Cathodoluminescence of wet, dry, and hydrogen-implanted silica films

The main luminescent centers in SiO2 films are the red luminescence R (1.85 eV) of the non-bridging oxygen hole center (NBOHC), a blue B (2.7 eV) band of the oxygen deficient centers (ODC’s), a UV (4.3 eV) band, and a yellow Y (2.2 eV) band appears especially in hydrogen-implanted silica after longer time of irradiation. By means of pulsed electron beam excitation and a new track–stop technique we have investigated the luminescence life time as well as the initial luminescence properties at the beginning of irradiation. Thus the dose dependence of the red (R) luminescence in wet and dry oxide differs, decreasing in wet oxide from an initial level and increasing in dry oxide from almost zero at room temperature. Additionally, implanted hydrogen diminishes the red luminescence in wet oxide but increases the blue and the UV bands. Thus hydrogen passivates the NBOHC and keeps the ODC’s in active emission states. A preliminary model of luminescence center transformation is based on radiolytic dissociation and re-association of mobile oxygen and hydrogen at the centers as well as formation of interstitial H2, O2, and H2O molecules. A comparison with the CL of ice layers shows that the H2O molecules should be the origin of the yellow (Y) luminescence.