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First-principle study of bismuth-related oxygen-deficient centers ($=$Bi$\cdots$Ge$\equiv$, $=$Bi$\cdots$Si$\equiv$, and $=$Bi$\cdots$Bi$=$ oxygen vacancies) in Bi$_2$O$_3$-GeO$_2$, Bi$_2$O$_3$-SiO$_2$, Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$, and Bi$_2$O$_3$-Al$_2$O$_3$-SiO$_2$ 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 $\mu$m and 1.8-3.0 $\mu$m ranges in Bi$_2$O$_3$-GeO$_2$ glasses and crystals is likely caused by $=$Bi$\cdots$Ge$\equiv$ and $=$Bi$\cdots$Bi$=$ centers, respectively, and the luminescence near 1.1 $\mu$m in Bi$_2$O$_3$-Al$_2$O$_3$-GeO$_2$ glasses and crystals may be caused by $=$Bi$\cdots$Ge$\equiv$ center with (AlO$_4$)$^-$ center in the second coordination shell of Ge atom., Comment: 5 pages, 3 figures, 25 references

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~$\mu$m range with a lifetime about 6~$\mu$s 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., Comment: 7 pages, 4 figures

Experimental and computer-modeling studies of spectral properties of crystalline AgCl doped with metal bismuth or bismuth chloride are performed. Broad near-IR luminescence band in the 0.8--1.2mkm range with time dependence described by two exponential components corresponding to the lifetimes of 1.5 and 10.3mks is excited mainly by 0.39--0.44mkm radiation. Computer modeling of probable Bi-related centers in AgCl lattice is performed. On the basis of experimental and calculation data a conclusion is drawn that the IR luminescence can be caused by Bi^+ ion centers substituted for Ag^+ ions., Comment: 5 pages, 5 figures

First-principle study of possible bismuth-related centers in SiO2 and GeO2 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, Bi^0; 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, Bi0 and Bi_2^-. Experimental data available on bismuth-related IR luminescence in SiO2:Bi and GeO2:Bi glasses, visible (red) luminescence in SiO2:Bi glass and the luminescence excitation are analyzed. Comparison of the calculated spectral properties of the bismuth-related centers with the experimental data shows that 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 probably responsible for the red luminescence in SiO2:Bi., Comment: 12 pages, 7 figures

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 observed in TlCl:Bi is most likely caused by Bi--Vac(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 observed in CsI:Bi., Comment: 8 pages, 4 figures

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 mkm excited by 0.40, 0.45, 0.70 and 0.80 mkm radiation, and a weak band at > 1.5 mkm excited by 0.40 and 0.45 mkm 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., Comment: 5 pages, 3 figures

IR luminescence and absorption in bismuth-doped silica glass-core fibers observed recently (see [arXiv:1106.2969v1 [physics.optics]) are argued to be caused by transitions in interstitial BiO molecules, Comment: 4 pages, 3 figures, 8 references

Subvalent bismuth centers (interstitial $Bi^{+}$ ion, Bi$_5^{3+}$ cluster ion, and Bi$_4^0$ cluster) are examined as possible centers of broadband near-IR luminescence in bismuth-doped solids on the grounds of quantum-chemical modeling and experimental data., Comment: 9 pages, 8 figures, 50 references

Precise measurement of the refractive index of stable silicon isotopes $^{28}$Si, $^{29}$Si, $^{30}$Si single crystals with enrichments above 99.9 at.% and a silicon single crystal $^{nat}$Si of natural isotopic composition is performed with the Fourier-transform interference refractometry method from 1.06 to more than 80 mkm with 0.1 cm$^{-1}$ resolution and accuracy of $2 \times 10^{-5} ... 1 \times 10^{-4}$. The oxygen and carbon concentrations in all crystals are within $5 \times 10^{15}$ cm$^{-3}$ and the content of metal impurities is $10^{-5} ... 10^{-6}$ at.%. The peculiar changes of the refractive index in the phonon absorption region of all silicon single crystals are shown. The coefficients of generalized Cauchy dispersion function approximating the experimental refractive index values all over the measuring range are given. The transmission and Raman spectra are also studied.

Absorption spectra of Ni$^{2+}$ ions in 22WO$_3$--78TeO$_2$ tungstate-tellurite glass were studied and Ni$^{2+}$ extinction coefficient spectral dependence was derived in the 450 -- 2700 nm wavelength range. Computer modeling of the glass structure proved Ni$^{2+}$ 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$^{2+}$ 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.

Absorption, luminescence and Raman spectra of interstitial bismuth atoms, $\mathrm{Bi}^{0}$, and negatively charged dimers, $\mathrm{Bi}^{2-}$, in alumosilicate, germanosilicate, phosphosilicate and phosphogermanate glasses networks are calculated by time-dependent density functional method. On grounds of this calculation an extension of our previously suggested model of broadband near-IR luminescence in bismuth-doped glasses is put forward., Comment: 14 pages, 5 figures, 1 table