We report spectral characteristics of amplified spontaneous emission (ASE) from an Er-Tm co-doped silica fiber. When pumped at 980 nm, the ASE yielded a 3 dB bandwidth over 90, 1460-1550 nm. The changes in ASE with regard to temperature, pumping scheme, and fiber lengths were measured experimentally, which strongly suggest that phonon-assisted energy transfer between the sensitizing ion, Er3+, and the acceptor ion, Tm3+, plays an important role in the bandwidth increment. (C) 2002 Elsevier Science B.V. All rights reserved.