The sol-emulsion-gel method is used for the preparation of Er3+ doped ZrO2 nanocrystals. The luminescence spectra and lifetime of the excited state I-4(13/2) of Er3+ ions in ZrO2 nanocrystals are found to be sensitive to the crystal structure and dopant concentration. It is found that the luminescence lifetimes of 1.0 mol% Er3+ doped ZrO2 nanocrystals are 1.94 and 3.36 ms for 800 and 1000 degreesC heat-treated samples, respectively. The analysis suggests that modification of relaxation mechanism is due to the crystal structure of the host and concentration of ions. (C) 2004 Elsevier B.V. All rights reserved.