Upconversion fluorescence of bismuth doped silica fibers

We investigated the upconversion fluorescence characteristics of bismuth doped silica fibers with and without Al co-dopant (BA fiber and BI fiber). Unusual upconversion fluorescence was discovered in both of these fibers when excited by pump lasers. After more experiments, it was found that the BI fiber showed a more complicated and distinct upconversion spectrum than the BA fiber, but with different and weaker NIR emission, as we reported before. Moreover, it was implied that the upconversion fluorescence must be mainly responsible for the Bi2+ ions in which the BI fiber was rich. Thus, properly improving the Al co-doping concentration could alleviate the upconversion fluorescence, thus improving the efficiency of the NIR band fluorescence. Besides, the complicated upconversion fluorescence bands may be helpful to clarify the energy levels of the Bi ions in silica materials.