Abnormal NIR photoemission from bismuth doped germanophosphate photonic glasses

Abstract

Bismuth (Bi)-activated glasses show great potential in novel optical amplifiers and tunable fiber lasers in a new region due to their super broadband NIR emission. However, the understanding of Bi NIR emission behaviors is still insufficient, which makes it challenging to manipulate Bi NIR emission in photonic glasses for efficient Bi-doped fibers and fiber lasers. Here, we report an unusual NIR luminescence behavior in Bi-doped germanophosphate glasses. Strong Bi NIR emission was observed in aluminophosphate and aluminogermanate glasses, while only weak NIR emission was observed in Bi-doped germanophosphate glasses, which is highly different from earlier reports. Detailed analysis on the optical and structural properties reveals that the changes in the Bi valence and distribution brought about by the addition of germanium are responsible for this. Moreover, the Bi ions tend to reside in the gap of the local glass network resulting from the depolymerization of the glass network, which leads to the aggregation of the Bi ions and consequent quenching of the Bi NIR emission. This work could enrich our understanding on Bi NIR emission behaviors in multi-component glasses. And Bi active centers with ultra-sensitive features may serve as optical probes for glass structures.