The influence of site occupancy of Li+, including substitutional and interstitial sites, on the upconversion emissions of Er3+ doped Y3Al5O12 powders is reported. The intensity of green emission increases slightly when the Li+ occupies substitutional site, but when the Li+ enters into interstitial site it enhances drastically accompanied with a change of emission spectra. These phenomena originate from the increase, induced by interstitial Li+, in the lifetime of I-4(11/2) level, the ratio of radiation rate in green emission and the absorptivity at 980 nm. (C) 2010 Elsevier B.V. All rights reserved.