Characteristics of diode-pumped Er-doped and Er–Pr-codoped ZBLAN fiber amplifiers were investigated at the $2.7–2.8\mu \mathrm{m}$ wavelength range. An amplified signal of $4.6\mathrm{W}$ was obtained from the singly Er-doped amplifier for an input signal of $110\mathrm{mW}$ , corresponding to a net gain of $16.2\mathrm{dB}$ . An amplified signal of $2.65\mathrm{W}$ was obtained from the Er–Pr-codoped amplifier for an input signal of $70\mathrm{mW}$ , corresponding to a net gain of $15.8\mathrm{dB}$ . It is found that the gain bandwidth of the singly Er-doped amplifier is much narrower than that of the Er–Pr-codoped amplifier. Small gain, no gain, or even a loss for shorter-wavelength signals propagating through the singly Er-doped amplifier should attribute for the large number residual populations in the lower laser level caused by the inefficient depopulation of the energy transfer upconversion processes.