Thermal behavior of NIR active centers in Bi-doped optical fibers
  The temperature dependences of optical loss and luminescence spectra have been measured in visible and NIR spectral range for Bi-doped silica and Bi-doped germanosilicate fibers for the first time. The temperature dependence of luminescence lifetime for Si-associated active bismuth centers in germanosilicate fiber was measured. It has been revealed, that distribution of Bi3+ ions across the fiber preform is essentially different as compared to that of NIR active bismuth centers. Data received indicates that NIR-active centers are associated with the low oxidation state of bismuth ion and/or oxygen deficient center of the glass structure. 
D.A. Dvoretsky, I.A. Bufetov, V.V. Vel'miskin, A.S. Zlenko, V.F.   Khopin, S.L. Semenov, A.N. Guryanov, L.K. Denisov, E.M. D...
physics.optics cond-mat.mtrl-sci