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The influence of site occupancy of Li(+), including substitutional and interstitial sites, on the upconversion emissions of Er(3+) doped Y(3)Al(5)O(12) 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 (4)I(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.