Bismuth (Bi)-doped NIR glass that can cover the entire optical communication window (850, 1310 and 1550 nm) has become the subjective of an entensive research for developing novel photonic devices, particularly, tunable fiber laser and ultra-broadband optical amplifier. However, the realization of highly efficient NIR luminescence from Bi-doped glass is still full of challenge. Notably, due to the co-existence of multiple Bi NIR centers in the glass, the origin of newly generated Bi NIR emission peaks at ~930 and ~1520 nm is still controversy. Here, we report a new Bi-doped nitridated germanate glass with tunable ultra-broadband NIR emission (850-1700 nm) and high external quantum efficiency (EQE) of ~50%. A series of studies including spectra analysis, NMR, and others provide powerful evidence for the mechanism of luminescence enhancement and tunability, and make reasonable inferences about the origin of the new emission bands at ~930 and ~1520 nm. We believe that the results discussed above would enrich our understanding about multiple Bi NIR emission behaviours and contribute to design and fabrication of highly efficient Bi-doped ultra-bradband wavelength-tunable optical glass fiber amplifiers and lasers in the future.