O2 molecules dissolved in synthetic silica glasses and their photochemical reactions induced by ArF excimer laser radiation

Abstract

Silica glasses were prepared by three different techniques, vapor phase axial deposition method, oxidation of SiCl4 in O2-H2 flame, and O2 or O2-Ar plasma method with changing preparation conditions. This was done with the expectation that O2 molecules dissolve in the glasses with different concentrations by using a wide variety of preparation conditions. O2 molecules were found to be dissolved in the order of 1017 cm−3 and give an optical absorption above 7 eV, the so-called Schumann–Runge bands. The estimations of concentrations were done by using a molar absorption coefficient of ≡SiOH at 0.46 eV formed under a reaction of O2 with H2 diffusing from atmosphere at high temperature, 1/2 O2+H2+≡Si−O−Si≡ →2≡Si−OH. The concentration directly estimated from the absorption intensity at above 7 eV was consistent with those estimated from the IR band of ≡SiOH. On the ArF excimer laser irradiation of the glasses which possess the absorption band above 7 eV, the well-known absorption band at 4.8 eV was induced. This band was assigned to the Hartley bands of the O3 molecule. The reaction model was proposed to be O2(trapped)→2O(hν>5.1 eV) and O+O2→O3(trapped). On exciting the induced 4.8 eV band, a photoluminescence at 1.9 eV was observed. The photoluminescence excitation spectrum of the band was agreed closely with the quantum yield curve of O(1D) on the excitation of Hartley bands of ozone. This suggests that the luminescence is due to the radiative relaxation of O(1D) to O(3P). The total reaction was proposed to be O3→O(1D)+O2 and O(1D)→O(3P)+1.9 eV.