V. G. Plotnichenko

Optical fibers based on As–S–Se glass system

The core-clad optical fibers with polymer coating based on As-S-Se glass have been manufactured with the aim of measuring their optical and strength parameters for potential use in the middle infrared. The glass compositions, As 40 S 30 Se 30 and As 40 S 33 Se 27 , were chosen as a core and a clad, respectively. To prepare sulfoselenide glasses and fibers we used two main variants, i.e., the direct melting of initial elements and using arsenic monosulfide as an arsenic-containing component. The core-clad-optical fibers were drawn by the double-crucible method with the ratio of core/ cladding diameters (in μm) 300/400, 200/400 and 100/400. The minimum loss measured by the two-point method was equal to 0.7 dB m 1 at 5.5 μm. It is the best result on As-S-Se core-clad fibers with comparable content of sulfur and selenium. The numerical aperture (NA), found as the sine of half of the angle of the power spatial distribution in the far zone, has also been measured in 2 fibers and is 0.35 and 0.2. The average mechanical bending strength was equal to 0.8 GPa.

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.

Optical absorption and structure of impurity Ni2+ center in tungstate–tellurite glass

Absorption spectra of Ni ions in 22WO3–78TeO2 tungstate-tellurite glass were studied and Ni extinction coefficient spectral dependence was derived in the 450 – 2700 nm wavelength range. Computer modeling of the glass structure proved Ni ions to be in trigonal-distorted octahedral environment in the tungstate-tellurite glass. Tanabe-Sugano diagram for such an environment was calculated and good description of the observed spectrum of Ni ion was obtained. Basing on both absorption spectral range width and the extinction coefficient, nickel should be considered among the most strongly absorbing impurities in the tellurite glasses.

Low-loss, high-purity (TeO2)0.75(WO3)0.25 glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO2)0.75(WO3)0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 102 cm−3, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm−1. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.

Infrared luminescence in Bi-doped Ge–S and As–Ge–S chalcogenide glasses and fibers

Experimental and theoretical studies of spectral properties of chalcogenide Ge–S and As–Ge–S glasses and fibers are performed. A broad infrared (IR) luminescence band which covers the 1.2 – 2.3 μm range with a lifetime about 6 μs is discovered. Similar luminescence is also present in optical fibers drawn from these glasses. Arsenic addition to Ge–S glass significantly enhances both its resistance to crystallization and the intensity of the luminescence. Computer modeling of Bi-related centers shows that interstitial Bi+ ions adjacent to negatively charged S vacancies are most likely responsible for the IR luminescence.

Centers of near-IR luminescence in bismuth-doped TlCl and CsI crystals

A comparative first-principles study of possible bismuth-related centers in TlCl and CsI crystals is performed and the results of computer modeling are compared with the experimental data. The calculated spectral properties of the bismuth centers suggest that the IR luminescence in TlCl:Bi is most likely caused by Bi(+)···V(Cl)(-) centers (Bi(+) ion in thallium site and a negatively charged chlorine vacancy in the nearest anion site). On the contrary, Bi(+) substitutional ions and Bi(2)(+) dimers are most likely responsible for the IR luminescence in CsI:Bi.

Preparation of single-crystal 29Si

A process has been developed for the preparation of single-crystal 29Si from 29Si-enriched silane. A silicon single crystal has been grown with a 29Si content over 99.9 at %. The oxygen and carbon concentrations in the crystal are under 1 × 1016 cm−3, and its resistivity exceeds 1 kΩ cm.

Effects of elevating temperature and high-temperature annealing upon state-of-the-art of yttia-alumino-silicate fibers doped with Bismuth

We report an experimental analysis of attenuation and fluorescence (at low-power 750-nm excitation) spectra’ transformations in yttria-alumino-silicate fiber doped with Bismuth (Bi), which occur at higher than room, but not exceeding 700°C, temperatures. As well, we address impact of elevating temperature upon the fiber’s basic characteristics, such as fluorescence/resonant-absorption saturation, fluorescence lifetime, and pump-light backscattering, given by the presence of Bi-Al related active centers (BACs). The experimental data reveals dramatic impact of heating and high-temperature annealing in excess of 500…550°C on the fiber’s state-of-the-art, expressed as significant rise of resonant absorption, enhancement of BACs NIR fluorescence, and reduction of scattering loss. In the meantime, such microscopic parameters of the fiber as BACs fluorescence lifetime and saturation power are found to be kept almost unchanged in its post-annealed state as compared to the pristine one. Possible mechanisms responsible for the phenomena and advantages of utilizing temperature-treated fiber of such type for lasing/amplifying purposes are discussed.

Specific absorption coefficient of cobalt(II) in (TeO2)0.80(MoO3)0.20 glass

We have prepared (TeO2)0.80(MoO3)0.20 glass samples containing 0.005–1.3 wt % cobalt(II) and investigated their optical transmission in the wavelength range 450–2800 nm. In this spectral region, the glasses have a strong absorption band centered at 1380 nm. From the dependence of electromagnetic radiation attenuation on cobalt concentration in the glasses, we have evaluated the specific absorption coefficient of Co2+ in the range 600–2800 nm. It has been found to be 18.4 ± 0.4 cm−1/wt % at the maximum of the 1380-nm absorption band.

Effect of Al and Ce ion concentrations on the optical absorption and luminescence in Gd3(Al,Ga)5O12:Ce3+ epitaxial films

We have studied the effect of Al and Ce ions on the optical absorption and luminescence of singlecrystal (Pb,Gd)3–yCeyAlxGa5–xO12 (x = 2.02, 2.09, 2.13, 2.17, 2.22; y = 0.02, 0.06, 0.07) films grown on (111)-oriented single-crystal Gd3Ga5O12 substrates by liquid-phase epitaxy from supercooled high-temperature solutions using solvents of the PbO–B2O3 system and growth charges containing 2.0, 2.1, or 2.2 mol % aluminum oxide and 0.03 or 0.2 mol % cerium oxide. The shift of the absorption bands of the Ce3+ 5d1 and 5d2 levels has been determined as a function of Al concentration in the films. The intensity of the Ce3+ luminescence bands of the films has been shown to increase with increasing Al and Ce concentrations.