Origin of broad NIR photoluminescence in bismuthate glass and Bi-doped glasses at room temperature

Bi-doped glasses with broadband photoluminescence in the near-infrared (NIR) spectral range are presently receiving significant consideration for potential applications in telecommunications, widely tunable fiber lasers and spectral converters. However, the origin of NIR emission remains disputed. Here, we report on NIR absorption and emission properties of bismuthate glass and their dependence on the melting temperature. Results clarify that NIR emission occurs from the same centers as it does in Bi-doped glasses. The dependence of absorption and NIR emission of bismuthate glasses on the melting temperature is interpreted as thermal dissociation of Bi₂O₃ into elementary Bi. Darkening of bismuthate glass melted at 1300°C is due to the agglomeration of Bi atoms. The presence of Bi nanoparticles is confirmed by transmission electron microscopy, high-resolution energy dispersive x-ray spectroscopy and element distribution mapping. By adding antimony oxide as an oxidation agent to the glass, NIR emission centers can be eliminated and Bi ³⁺ is formed. By comparing with atomic spectral data, absorption bands at ∼320, ∼500, 700, 800and 1000nm observed in Bi-doped glasses are assigned to Bi⁰ transitions, and respectively, and broadband NIR emission is assigned to the transition .