V. O. Sokolov

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

Interstitial negative-charged bismuth dimers, Bi(-)(2) and Bi(2-)(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.

On the structure of phosphosilicate glasses

Abstract Vibrational spectra of phosphosilicate glasses with P 2 O 5 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PO 3 tetrahedra surrounded by SiO 4 ones) and by double phosphorus centers (pairs of OPO 3 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.

Cluster modeling of the neutral oxygen vacancy in pure silicon dioxide

Abstract The main results of the computer simulation of the oxygen vacancy in pure silicon dioxide are presented. The semi-empirical method, MNDO from the MOPAC package, is used. Silicon dioxide is simulated by molecular clusters of different sizes and structures. Calculated positions of the absorption and luminescence bands of the neutral oxygen vacancy are in satisfactory agreement with those of the oxygen-deficient center observed in pure silicon dioxide. The absorption and luminescence bands of the vacancy correspond to the dipole allowed one-electron transitions between two localized states with the levels in the energy gap of SiO2. The lower level is doubly occupied; the upper one is empty, resulting from the bonding and antibonding combination of sp orbitals of two silicon atoms adjacent to the vacant site, respectively.

Raman band intensities of 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.

Centres of broadband near-IR luminescence in bismuth-doped glasses

Interstitial negative-charged bismuth dimers, and , are suggested as a model of broadband near-IR luminescence centres 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 and visible luminescence observed for the first time in bismuth-doped polycrystalline magnesium cordierite and by Raman spectra measurements in optical fibres with bismuth-doped alumosilicate glass core.Interstitial negative-charged bismuth dimers, and , are suggested as a model of broadband near-IR luminescence centres 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 and visible luminescence observed for the first time in bismuth-doped polycrystalline magnesium cordierite and by Raman spectra measurements in optical fibres with bismuth-doped alumosilicate glass core.

Structure of WO3-TeO2 glasses

WO3-TeO2 glasses have been studied by quantum-chemical simulation and Raman spectroscopy. The results have been used to develop a model for the network of tungstate-tellurite glasses. The model allows one to correlate the structure and optical properties (in particular, the position and intensity of Raman bands) of the glasses with their composition. The network of the glasses is shown to be made up, for the most part, of three types of structural groups: TeO4 trigonal dipyramids, O=TeO2 pyramids, and O=WO5 octahedra. Any other structural units, in particular, WO4 tetrahedra, are unnecessary. The model for the network of WO3-TeO2 glasses can be used to analyze the vibrational spectra of tungstate-tellurite glasses in a broad composition range. In particular, using this model we assigned the Raman spectra of the tungstate-tellurite glasses in the range 550–950 cm−1.

The origin of near-IR luminescence in bismuth-doped silica and germania glasses free of other dopants: First-principle study

First-principle study of possible bismuth-related centers in SiO2 and GeO2 glass model hosts is performed and the results are compared with the experimental data. The following centers are modeled: trivalent and divalent Bi substitutional centers; BiO interstitial molecule; interstitial ion, Bi+, and atom, Bi0; Bi··· ≡Si–Si≡ and Bi··· ≡Ge–Ge≡ complexes formed by interstitial Bi atoms and glass intrinsic defects, ≡Si–Si≡ or ≡Ge–Ge≡ oxygen vacancies; interstitial dimers, Bi20 and Bi2−. Experimental data available on bismuth-related IR luminescence in SiO2:Bi and GeO2:Bi glasses, visible (red) luminescence in SiO2:Bi glass and luminescence excitation are analyzed. A comparison of calculated spectral properties of bismuth-related centers with the experimental data shows that the IR luminescence in SiO2:Bi and GeO2:Bi is most likely caused by Bi··· ≡Si–Si≡ and Bi··· ≡Ge–Ge≡ complexes, and divalent Bi substitutional center is responsible for the red luminescence in SiO2:Bi.

Semiempirical calculations of point defects in silica. Oxygen vacancy and twofold coordinated silicon atom

Abstract Structure and electronic properties of oxygen vacancy and twofold coordinated silicon atom in solid silicon dioxide are investigated in a cluster approach by MNDO semiempirical molecular orbital method. Optical absorption and photoluminescence bands are calculated. Two types of the neutral oxygen vacancy are predicted absorbing at 5.3 eV and at 7.8 eV. Calculated properties of the first vacancy agree with the experiment for oxygen-deficient centres in silica glass and may be regarded as a confirmation of corresponding model of these centres. Contradictions between recent tight-binding and ab initio calculations of the oxygen vacancy are resolved.

Near-infrared luminescence in TlCl:Bi crystal

Experimental and theoretical studies of spectral properties of crystalline TlCl:Bi are performed. Two broad near-infrared luminescence bands with a lifetime about 0.25 ms are observed: a strong band near 1.18 μm excited by 0.40, 0.45, 0.70 and 0.80 μm radiation, and a weak band at & 1.5 μm excited by 0.40 and 0.45 μm radiation. Computer modeling of Bi-related centers in TlCl lattice suggests that Bi · · ·V− Cl center (Bi in Tl site and a negatively charged Cl vacancy in the nearest anion site) is most likely responsible for the IR luminescence.Experimental and theoretical studies of spectral properties of crystalline TlCl:Bi are performed. Two broad near-infrared luminescence bands with a lifetime of about 0.25 ms are observed: a strong band near 1.18 μm excited by 0.40, 0.45, 0.70, and 0.80 μm radiation and a weak band at ≳1.5 μm excited by 0.40 and 0.45 μm radiation. Computer modeling of Bi-related centers in TlCl lattice suggests that a Bi(+)…VCl(Cl)(-) center (Bi(+) in Tl site and a negatively charged Cl vacancy in the nearest anion site) is most likely responsible for the IR luminescence.

Origin of near-IR luminescence in Bi 2 O 3 –GeO 2 and Bi 2 O 3 –SiO 2 glasses: first-principle study

First-principle study of bismuth-related oxygen-deficient centers (=Bi · · ·Ge≡, =Bi · · ·Si≡, and =Bi · · ·Bi= oxygen vacancies) in Bi2O3–GeO2, Bi2O3–SiO2, Bi2O3–Al2O3–GeO2, and Bi2O3–Al2O3–SiO2 hosts is performed. A comparison of calculated spectral properties of the centers with the experimental data on luminescence emission and excitation spectra suggests that luminescence in the 1.2 – 1.3 μm and 1.8 – 3.0 μm ranges in Bi2O3–GeO2 glasses and crystals is likely caused by =Bi · · ·Ge≡ and =Bi · · ·Bi= centers, respectively, and the luminescence near 1.1 μm in Bi2O3–Al2O3–GeO2 glasses and crystals may be caused by =Bi · · ·Ge≡ center with (AlO4) − center in the second coordination shell of Ge atom.First-principle study of bismuth-related oxygen-deficient centers (=Bi···Ge≡, =Bi···Si≡, and =Bi···Bi= oxygen vacancies) in Bi2O3–GeO2, Bi2O3–SiO2, Bi2O3–Al2O3–GeO2, and Bi2O3–Al2O3–SiO2 hosts is performed. A comparison of the calculation results with the experimental emission and excitation spectra of IR luminescence suggests that luminescence in the 1.2–1.3 μm and 1.8–3.0 μm ranges in Bi2O3–GeO2 glasses and crystals is likely caused by =Bi···Ge≡ and =Bi ···Bi= centers, respectively, and the luminescence near 1.1 μm in Bi2O3–Al2O3–GeO2 glasses and crystals may be caused by =Bi···Ge≡ center with (AlO4)− center in the second coordination shell of Ge atom.