Tellurite fibers with 7500 ppm Er3+ concentration and diverse 2500-15,000 ppm Tm3+ concentrations were manufactured, and their amplified spontaneous emission (ASE) intensities 1550 nm band around were obtained for 980 and 790 nm pump laser. Maxima 187 nm bandwidth at -3 dB points using Er3+-Tm3+ co-doped tellurite optical fibers pumping at 790 nm was obtained, and energy transfer (ET) process between I-4(13/2) Er3+ and F-3(4) Tm3+ levels related with the amplifier quantum efficiency was studied from experimental and calculated lifetime. (c) 2005 Elsevier Inc. All rights reserved.122185195