Synthetic high purity glassy silicon dioxide (g-SiO₂) is important material in applications using optical fibers, high-power laser optics, radiation-resistant and UV transmitting elements. The operation of these devices is adversely affected by creation of point defects. Their formation mechanism in g-SiO2 is often different from mechanisms, typically taking place in crystalline materials or multicomponent glasses. Instead of electron/hole trapping on preexisting precursors, the majority of radiation-induced defects in g-SiO₂ is created in photochemical reactions, involving monovalent impurities (mostly hydrogen) and interstitial gas molecules.

The talk will give a brief overview of the properties of different gas molecules observed in g-SiO₂ (H₂, O₂, O₃, H₂O, HCl, Cl₂), their spectroscopic properties and their impact on radiation toughness of g-SiO₂ optical devices. More details will be given on interstitial oxygen and chlorine molecules and our recent studies of these species will be discussed.

Interstitial oxygen atom, possibly in the form of Si-O-O-Si peroxy linkage, has not been experimentally observed in SiO₂.  On the other hand, its dimerized form, interstitial O₂ molecule, can be monitored by its distinct IR luminescence. By using it, the defect formation and isotope exchange between of O₂ and SiO₂ network was studied. 

Apart from intrinsic radiation effects, optical properties of synthetic SiO₂ are often affected by the presence of chlorine impurities left from the synthesis process.  We have recently proved that interstitial Cl₂ molecules in g-SiO₂ show characteristic near-IR luminescence, which can be excellently used for detection of their presence and for studying their photo- or radiation-induced -reactions in g-SiO₂.  The present data indicate that Cl₂ molecule is strongly stabilized against dissociation by SiO₂ glass matric ("cage effect").

Séminaire invité par Nadège Ollier.