Uniform square-shaped Y4O(OH)(9)(NO3) nanoplates with side length of about 300 nm and thickness of tens of nanometers have been successfully prepared by an ionic liquid-assisted mixed solvothermal route. Y2O3 nanoplates with similar size were obtained after calcining the Y4O(OH)(9)(NO3) nanoplates at 800 degrees C. The products were analyzed by powder X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM (HRTEM), and electron diffraction (ED). The effects of reaction time, composition of solvents, and the molar ratio of reagents on the morphology of the products have been investigated. The possible formation mechanism of the Y4O(OH)(9)(NO3) nanoplates was also discussed. Y2O3:Eu3+ nanoplates were also synthesized and their photoluminescent properties were examined. (C) 2014 Elsevier Ltd. All rights reserved.