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~$\mu$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. 
V. G. Plotnichenko, D. V. Philippovskiy, V. O. Sokolov, M. V.   Sukhanov, A. P. Velmuzhov, M. F. Churbanov, and E. M. Dianov
cond-mat.mtrl-sci physics.optics