Near-infrared luminescence in bismuth-doped TlCl 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 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.

Possible centers of broadband near-IR luminescence in bismuth-doped solids: $Bi^{+}$, Bi$_5^{3+}$, and Bi$_4^0$

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.

Optical absorption and structure of impurity Ni$^{2+}$ center in tungstate-tellurite glass

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.