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The support from M -ERANET project "MyND" is acknowledged. K.K. was partially supported by the Collaborative Research Project of Laboratory for Materials and Structures, Tokyo Institute of Technology . Visiting researcher support from Ecole Polytechnique, Palaiseau is appreciated. Mr. Olivier Cavani is thanked for the expert help with irradiations. ; Point defects in crystalline SiO2, created by 2.5 MeV electron irradiation at dose below the amorphization threshold or by fast neutrons, were compared by luminescence spectroscopy. Oxygen dangling bonds ("non-bridging oxygen hole centers", NBOHCs), peculiar to amorphous state of SiO2, were detected for the first time in electron-irradiated non-amorphized α-quartz crystal. Their presence may signal the formation of nucleation centers in crystal structure as the first step to radiation-induced amorphization. Compared to crystal, irradiated by 1019 cm−2 fast neutrons, their concentration was over 100 times lower, and their inhomogeneous broadening was at least 2.5 times smaller. Divalent silicons ("silicon oxygen deficiency centers", SiODC(II)), inherent to oxygen-deficient or irradiated SiO2 glass, were detected in neutron-irradiated (1019 n/cm2) α-quartz but were not found after the electron irradiation. Radiation-induced interstitial O2 molecules, characteristic to irradiated glassy SiO2 and other oxide glasses, are found in α-quartz only after neutron irradiation. The oxygen atoms, displaced by the 2.5 MeV e− irradiation of α-quartz for fluences up to 1019 e−/cm2 evidently stays entirely in the peroxy linkage (Si-O-O-Si bond) form. ; M -ERANET; Tokyo Institute of Technology; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The support from the Latvian Research Program project IMIS 2 (L.S., K.S.) and Latvian Science Council Grant 302/2012 (A.S.) is acknowledged. K.K. was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology. H.H. was supported by the MEXT Element Strategy Initiative to form research cores. ; Chlorine is a common undesirable impurity in synthetic SiO2 glass for ultraviolet optics and optical fibers. It is usually incorporated into glass as bound Si-Cl groups or interstitial Cl2 molecules. We report a high-sensitivity detection of Cl2 in amorphous SiO2 (a-SiO2) by photoluminescence (PL) and also by Raman spectroscopy. The Cl2 PL emission band at 1.22 eV (1016 nm) appears at T < 160 K and shows a characteristic vibronic progression with separations ≈(520-540) cm-1 and an average lifetime of ≈5 ms at 13 K. Its excitation spectrum coincides with the shape of the 3.78 eV (328 nm) optical absorption band of Cl2 in a-SiO2, corresponding to the X → A 1Πu transition to repulsive excited state. Direct X → a singlet-to-triplet excitation was also observed at 2.33 eV (532 nm). Cl2 PL may serve as a sensitive and selective tool for monitoring Cl impurities and their reactions in a-SiO2. A Raman band of Cl2 is found at 546 cm-1. Cl2 photodissociation at energies up to 4.66 eV (266 nm) was not detected, pointing to a strong cage effect in a-SiO2 matrix. However, 7.9 eV (157 nm) photolysis of interstitial O2 molecules gives rise to a Raman band at 954 cm-1, indicating a formation of dichlorine monoxide isomer, ClClO molecule by reaction of O atoms with interstitial Cl2. (Graph Presented). ; IMIS2; Latvian Science Council Grant 302/2012; Tokyo Institute of Technology; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The support from Latvian Research Program IMIS 2, project "Photonics and materials for photonics" is acknowledged. K.K. was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology. The publication costs of this article were covered by the Estonian Academy of Sciences and the University of Tartu. ; Glassy SiO2 is the basic material for optical fibre waveguides and manufacturing-induced Cl impurities reduce their transparency in UV spectral range. This work reports in-depth study/spectroscopic parameters of the near-infrared (1.23 eV) low-temperature photo-luminescence (PL) of interstitial Cl2 molecules in SiO2. The zero-phonon line position was estimated at 2.075 eV on the basis of anharmonicity of Cl2 PL vibronic data. The vibronic sub-bands are broadened by coupling to phonons and by an additional contribution from the glassy disorder. The Huang‒Rhys factor is ≈13. The PL decay time is between 1 and 10 ms in the temperature range 100 K‒13 K and can be reproduced by 3 exponents. Cl2 PL retains relatively high quantum yield and its characteristic structured shape, when the temperature is increased from 13 K to the liquid nitrogen temperature. This allows using it conveniently as a high-sensitivity diagnostic tool for detecting Cl2 impurities in optical fibre waveguides. Time-resolved measurements of optical fibre waveguides indicate that the lower detection limit is below 1010 Cl2/cm3. ; Tokyo Institute of Technology, MSD K.K.,Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART².