摘要： Nanocrystalline Eu3+:CeO2-SiO2 powder samples were prepared by sol-gel technique. This technique is suitable for large-scale production and it is also a cost effective process. The prepared samples were annealed at different temperatures which were characterized by many complementary techniques. The formation of cubic fluorite structure of CeO2 nanocrystal with a uniform distribution was confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The average nanocrystalline size has been calculated as 3, 7 and 15 nm using Debye-Scherrer formula for different annealed samples. The calculated nanocrystalline sizes were compared with W-H plot and TEM histograms. It was investigated that FWHM of diffraction peaks decreases with increase in temperature results in increase nanocrystalline size. The FTIR spectroscopy provides the valuable information and identification of different chemical group/bonds present in the prepared samples. It is found that if we fixed the dopant concentration, then particle size, morphology and band gap energy of prepared nanopowder can be tailored by applying the annealing conditions. Comparative studies of absorption spectra and corresponding band gap energies have been done and a red shift has been observed in absorption spectra with thermal treatment. The shift of the optical absorption edge of prepared nanopowder towards lower energies increases its utilization in the visible region specially photocatalytic activity.