IR luminescence in bismuth-doped germanate glasses and fibres

We have studied the optical properties of lightly bismuth doped (<= 0.002 mol%) germanate glasses prepared in an alumina crucible. The glasses are shown to contain bismuth-related active centres that have been identified previously only in bismuth-doped fibres produced by MCVD. With increasing bismuth concentration in the glasses, their luminescence spectra change markedly, which is attributable to interaction between individual bismuth centres.