  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.
