When Er-doped materials are pumped by 980nm laser, they can emit the light at 1550nm as well as green light due to the energy transfer between different energy level. When all the emission energy come from the pump light, the up-conversion green light should be suppressed in order to maximize the emission energy at 1550nm which is the important for optical amplification at telecommunication wavelength. The question is thus that, how to suppress the up-conversion emission in Er-doped materials and therefore most of the pump energy can be converted into 1550nm?