Peculiarities of photoluminescence excited by 157 nm wavelength F2 excimer laser in fused and unfused silicon dioxide

Photoluminescence (PL) spectra and kinetics of high purity amorphous silicon dioxide with ultra low hydroxyl content is studied under the excitation by F₂ excimer laser (157 nm wavelength) pulses. Materials synthesized in the SPCVD plasma chemical process are studied before and after fusion. Two bands are found in the PL spectra: one centered at 2.6–2.9 eV (a blue band) and the other at 4.4 eV (a UV band). Luminescence intensity of unfused material is found to increase significantly with exposure time starting from a very small level, whereas in fused counterpart it does not depend on irradiation time. Both bands show complicated decay kinetics, to which add exponential and hyperbolic functions. The UV band of the unfused material is characterized by decay with exponential time constant τ  4.5 ns and hyperbolic function t⁻ⁿ, where n = 1.5 ± 0.4. For the blue band the hyperbolic decay kinetics with n  1.5 extends to several milliseconds, gradually transforming to the exponential one with τ = 11 ± 0.5 ms. In fused glass relative contribution of the fast component to the UV band is small whereas for the blue one it is great, that allows one to more accurately determine the hyperbolic law factor n = 1.1 ± 0.1 typical for tunneling recombination. Simultaneous intracenter and recombination luminescence, the later occurring with the participation of laser radiation induced defects, add particular features to the decay kinetics. Spectra of the above luminescence processes are different. A less sharp position of bands is associated with the recombination luminescence. The origin of the observed PL features we attribute to the presence of oxygen deficient centers in glass network in the form of twofold coordinated silicon. Such centers being affected by network irregularities can be responsible for the recombination PL component. A great variety of network irregularities is responsible for centers’ structural inequivalence, which causes a non-uniform broadening of PL spectral and kinetic parameters.