Interstitial BiO molecule as a center of broadband IR luminescence in   bismuth-doped silica glass
  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 
V.O.Sokolov, V.G.Plotnichenko, E.M.Dianov
cond-mat.mtrl-sci physics.optics