Regulating the Bi NIR luminescence behaviours in fluorine and nitrogen co-doped germanate glasses

Abstract

Bi-Doped nitridated germanate glasses covering the whole NIR region from 800–1600 nm have attracted considerable attention due to their potential application in tunable fiber lasers and optical amplifiers. However, it remains challenging to regulate the luminescence behaviour of Bi because of the coexistence of multi-centers in the glasses. Here, we successfully regulated multi Bi NIR centers to obtain a flatter and ultra-broadband emission in nitridated germanate glasses. By varying the alkaline earth metal fluorides from MgF₂ to BaF₂, the glass structures were gradually depolymerized. A looser glass network, on one hand, promoted Bi in lower valences to be oxidized into Bi²⁺ and Bi³⁺, thus reducing the NIR emission intensity at ∼1150 and ∼1260 nm; on the other hand, it also enhanced the energy transfer from Bi⁺ to Bi⁰, which resulted in a relatively flatter emission band. In addition, the depolymerised glass structure could facilitate more nitride bonds, which are favorable for dispersing and stabilizing the new Bi NIR active centers related to germanate for ∼930 and ∼1490 nm emission. This investigation offers an efficient way to manipulate the multi-center luminescence behaviour of Bi in nitridated germanate glasses, and is beneficial to understand the mechanism of Bi NIR emission centers in glasses.