Enhanced 2.7 \mu m emission is obtained in Er3+/Tm3+ and Er3+/Ho3+ codoped ZBYA glasses. Absorption and emission spectra are tested to characterize the 2.7 \mu m emission properties of Er3+/Tm3+ and Er3+/Ho3+ doped ZBYA glasses and a reasonable energy transfer mechanism of 2.7 \mu m emission between Er3+ and Tm3+Ho3+) ion is proposed. Codoping of Tm3+ or Ho3+ significantly reduces the lifetime of the Er3+: 4I13/2 level due to the energy transfer of Er3+:4I13/2 ?Tm3+:3F4 or Er3+:4I13/2 ?Ho3+: 5I7. Thus, the 2.7 \mu m emission is strengthened and the 1.5 \mu m emission is decreased accordingly especially in the Er3+/Tm3+ sample. The upconversion effects between the Er3+/Tm3+ and Er3+/Ho3+ doped ZBYA glasses are different attribute to the different energy transfer efficiencies. Both of the two codoped samples possess nearly equal large emission cross section (16.6 \times 10-21 cm-2) around 2.7 \mu m. The results indicate that this Er3+/Tm3+ or Er3+/Ho3+ doped ZBYA glass has potential applications in 2.7 -m laser.