Interband decay and absorption mechanisms in amorphous silica probed by synchrotron light

Amorphous silica is a key material in many technological fields from microelectronics to fibre optics. The knowledge advancement in the photophysics of SiO2 is of relevant importance not only for all these applications, but also for the general scientific community involved in the study of photonic materials and amorphous systems. Here, I present recent results on the principle fundamental aspects involved in the exciton decay mechanism of various SiO2-based glasses. The starting point of this analysis is based on advanced spectroscopic experiments conducted at the SUPERLUMI experimental station of HASYLAB at DESY (Hamburg, Germany) and using synchrotron light as excitation source which is a unique choice for photophysical measurements involving high-energy photons. Decay mechanisms of above band gap excitations (photon energy > 9.8 eV) have been studied as a function of temperature in a large set of SiO2 glasses and crystals synthesized by different production method and including different perturbation level of the structural network, from nominally pure parent samples to samples conditioned by doping or by treatment-induced defects. Here, I will show that band-to-band excitations decay occurs into two competitive channels with red and green emissions so far ascribed to recombination involving non-bridging oxygen and self-trapped exciton, respectively. Interestingly, these two configurations are not independent, but they are the result of a common de-excitation path as evidenced by the presence of an isostilbic point in the temperature-dependent emission spectra. Finally, I will demonstrate a general relationship between exciton spectral position and bandwidth which clarifies the role of disorder in above band gap reflectivity spectra.