The spectroscopic properties, structure and interconversions of optically active oxygen-deficiency-related point defects in vitreous silica are reviewed. These defects, the E′-centers (oxygen vacancies with a trapped hole or 3-fold-coordinated silicons), different variants of diamagnetic `ODCs' (oxygen-deficiency centers), and their Ge-related analogs play a key role in the fiber-optic Bragg grating writing processes. The controversy surrounding the structural models for the Si- and Ge-related ODCs is discussed and the similarity between the bulk and surface point defects in silica is emphasized. The possible interconversion mechanisms between 2-fold-coordinated Si, neutral oxygen vacancies and E′-centers are discussed. The effects of glassy disorder have a profound effect on defect properties and interconversion processes in silica.

Optically active oxygen-deficiency-related centers in amorphous silicon dioxide

We thoroughly and critically review studies reporting the real (refractive index)
 and imaginary (absorption index) parts of the complex refractive index of silica glass
 over the spectral range from 30 nm to 1000 μm The general features of the optical
 constants over the electromagnetic spectrum are relatively consistent throughout the
 literature In particular, silica glass is effectively opaque for wavelengths shorter
 than 200 nm and larger than 35-40 μm Strong absorption bands are observed (i) below
 160 nm due to the interaction with electrons, absorption by impurities, and the presence
 of OH groups and point defects; (ii) at ~273-285, 35, and 43 μm also caused by OH
 groups; and (iii) at ~9-95, 125, and 21-23 μm due to SiOSi resonance modes of
 vibration However, the actual values of the refractive and absorption indices can vary
 significantly due to the glass manufacturing process, crystallinity, wavelength, and
 temperature and to the presence of impurities, point defects, inclusions, and bubbles,
 as well as to the experimental uncertainties and approximations in the retrieval
 methods Moreover, new formulas providing comprehensive approximations of the optical
 properties of silica glass are proposed between 7 and 50 μm These formulas are
 consistent with experimental data and substantially extend the spectral range of 021-7
 μm covered by existing formulas and can be used in various engineering applications

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Optical constants of silica glass from extreme ultraviolet to far infrared at near room temperature.

The family of oxide glasses is very wide and it is continuously developing. The rapid development of advanced and innovative glasses is under progress. Oxide glasses have a variety of applications in articles for daily use as well as in advanced technological fields such as X-ray protection, fibre glasses, optical instruments and lab glassware. Oxide glasses basically consist of network formers, such as borate, silicate, phosphate, borosilicate, borophosphate, and network modifiers such as alkali, alkaline earth and transition metals. In the present review article, Raman spectroscopy results for the structures of borate, silicate, phosphate, borosilicate, borophosphate, aluminosilicate, phosphosilicate, alumino-borosilicate and tellurite glasses are summarized.

A review of the structures of oxide glasses by Raman spectroscopy

In this review paper, we present radiation effects on silica-based optical fibers. We first describe the mechanisms inducing microscopic and macroscopic changes under irradiation: radiation-induced attenuation, radiation-induced emission and compaction. We then discuss the influence of various parameters related to the optical fiber, to the harsh environments and to the fiber-based applications on the amplitudes and kinetics of these changes. Then, we focus on advances obtained over the last years. We summarize the main results regarding the fiber vulnerability and hardening to radiative constraints associated with several facilities such as Megajoule class lasers, ITER, LHC, nuclear power plants or with space applications. Based on the experience gained during these projects, we suggest some of the challenges that will have to be overcome in the near future to allow a deeper integration of fibers and fiber-based sensors in radiative environments.

Radiation Effects on Silica-Based Optical Fibers: Recent Advances and Future Challenges

The recent results on the new laser material – Bi-doped glasses and optical fibers are reviewed. First, luminescence properties of various Bi-doped glasses are discussed. At last the results of investigations of Bi-doped fiber lasers covering a wavelength range of 1150 – 1550 nm are presented.

https://iopscience.iop.org/article/10.1002/lapl.200910025/pdf

Bi-doped fiber lasers

Interstitial negative-charged bismuth dimers, Bi−2 and Bi2−2, are suggested as a model of broadband IR luminescence centers in bismuth-doped glasses. The model is based on quantum-chemical calculations of equilibrium configurations, absorption, luminescence, and luminescence excitation spectra of the dimers in an alumosilicate network and is supported by IR luminescence observed for the first time, to our knowledge, in bismuth-doped polycrystalline magnesium cordierite.

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Origin of broadband near-infrared luminescence in bismuth-doped glasses

Vibrational spectra of phosphosilicate glasses with P2O5 concentrations up to 15 mol% are investigated by the methods of Raman spectroscopy and quantum-chemical modeling. We have found that the Raman band at 1320 cm−1 characteristic for such glasses is not simple and may be decomposed into two components with frequencies at ≈1317 and ≈1330 cm−1 caused in our opinion by single phosphorus centers (OPO3 tetrahedra surrounded by SiO4 ones) and by double phosphorus centers (pairs of OPO3 tetrahedra bonded by a common oxygen atom). In the investigated phosphosilicate glasses manufactured by MCVD and SPCVD methods the ratio of concentrations of single and double centers varies from 1:5 to 1:2. A novel interpretation of the Raman bands distinct from the traditional one is suggested. The approach to the Raman spectra analysis developed in this article can be applied for control and optimization of manufacturing process of phosphosilicate and similar glasses as well as optical fibers.

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On the structure of phosphosilicate glasses

A continuous network model of x WO 3 –(1 −  x )TeO 2 glasses is developed, based on quantum-chemical calculation and Raman spectra analysis, in order to relate the structural and vibrational properties with glass composition. The tungstate–tellurite glass network is shown to be formed mainly by structural units of three types, TeO 4 trigonal bipyramids, O TeO 2 trigonal pyramids, and WO 6 octahedra with O W double bonds. Most of the W atoms are found to be incorporated into single O WO 5 octahedra, with no more than several percents of these atoms occurring in 2[O WO 5 ] paired tungstate centers. The structural and vibrational properties of tungstate–tellurite glasses of several compositions are analyzed by application of the model and a novel interpretation of the Raman spectra is suggested.

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On the structure of tungstate–tellurite glasses

Raman spectra of TeO2-based glasses doped with WO3, ZnO, GeO2,TiO2,MoO3, and Sb2O3 are measured. The intensity of bands in the Raman spectra of MoO3–TeO2 and MoO3–WO3–TeO2 glasses is shown to be 80–95 times higher than that for silica glass. It is shown that these glasses can be considered as one of the most promising materials for Raman fiber amplifiers.

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Raman band intensities of tellurite glasses

The IR absorption spectra of the high-purity commercial silica glasses KU, KV., KUVI, KI, and KS-4V., containing from 10-1 to 103 ppm hydroxyl groups, were measured. Based on the experimental data and quantum-chemical calculations, a new approach to the description of the OH incorporation in the glass network was proposed. Our results suggest that, in high-purity SiO2, the OH groups exist as isolated units, rather than as bonded pairs, and a fraction of the OH groups are hydrogen-bonded to bridging oxygens, in contrast to what was generally believed earlier. A new decomposition of the fundamental OH-stretching band is proposed.

V. O. Sokolov

Papers

Origin of broadband near-infrared luminescence in bismuth-doped glasses

On the structure of phosphosilicate glasses

On the structure of tungstate–tellurite glasses

Raman band intensities of tellurite glasses

Hydroxyl groups in high-purity silica glass