Study On Bi-doped Tantalum Germanate Glasses With Near-infrared Luminescence

With the development of the information society, data are playing a more and more important role in human society. People’s requirement for data is more exigent than any times before. So, more researches are focusing on high-speed and large-capacity optical fiber communication system. Broadband optical fiber amplifier is the key component to large-capacity optical fiber communication system. However, traditional rare earth ion-doped fiber amplifiers have inevitable defect, such as limited bandwidth which is difficult to surpass 100 nm. Compared with rare earth ion, bismuth can show broadband near-infrared(NIR) emission(1000~1600 nm) in various glass matrix which can completely cover the silica fiber low loss communication window. So, NIR emitting bismuth-doped glass is considered as one promising candidate material for broadband optical fiber amplifier.In this paper, we have systematically studied bismuth-doped tantalum germanate glass which has strong NIR emission as previous reports suggest.We have studied the influence of melting time on the homogeneity and NIR fluorescence of bismuth-doped tantalum germanate glass. Prolonging the glass melting time can improve sample’s homogeneity and also cause enhanced bismuth volatilization in the meantime. So to reduce bismuth volatilization, we introduce alkali metal oxide to lower melting temperature. However, as alkali metal oxide concentration increases, glass phase separation happens to the samples. In the same time, alkali metal oxide makes the glass microstructure change and sample NIR emission intensity decrease. Here we have studied the relation between alkali metal oxide concentration, glass microstructure and sample NIR fluorescence.As bismuth NIR fluorescence is sensitive to composition, its emission wavelength varies with sample composition. We have established quantitative empirical prediction laws which enable to predict the frequency shift of NIR luminescence from bismuth-doped tantalum germanate glasses with different Ta2O5 and Bi2O3 concentration. This is a good guide to the composition design of bismuth-doped glasses.Base on excitation and emission spectra of different samples, we have also discussed bismuth NIR luminescence mechanism. We found that the NIR luminescence of bismuth-doped glasses come from different bismuth active-centers.Considering the environment in which the bismuth-doped glass materials are used in the future, we have studied the impact of high temperature on the NIR fluorescence of bismuth-doped tantalum germanate glass. In the samples with different Ta2O5 or Bi2O3 concentration, the attenuation of NIR emission intensity caused by high temperature can recover as temperature drops. However, the recovery gradually becomes impossible as Li2 O concentration increases.To explore the feasibility of fiber fabrication of bismuth-doped tantalum germanate glass using rod-in-tube fiber drawing technique, we have studied the thermal property of the glass. As heat treatment temperature increases, Ta2O5 and Ge O2 crystal successively appear in the tantalum germanate glass. The softening temperature of tantalum germanate glass is high. So we introduce Li2 O to reduce glass softening temperature. However, thermal stability of bismuth active-centers decreases as Li2 O concentration increases.