Growth and optical properties of cerium dioxide nanocrystallites prepared by coprecipitation routes

Nanosized cerium dioxide (CeO2) powders have been synthesized using coprecipitation methods and cerium nitrate hexahydrate (Ce(NO3)3·6H2O) as the starting material. The growth and optical properties of nanosized CeO2 powders were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano-beam electron diffraction (NBED), high resolution TEM (HRTEM), and ultraviolet–visible (UV–vis) absorption spectrophotometry. The XRD result shows that the dried CeO2 precursor powders (both before and after calcination at various temperatures and times) contained a single crystalline phase of CeO2. In the dried precursor powders, the crystallites of CeO2 measured 10.4 nm and 66.8 nm before and after calcination at 1273 K for 240 min, respectively. The indirect band gap energy (EiEi) of CeO2 decreased from 3.03 eV to 2.68 eV as the crystallite size increased from 10.4 nm to 66.8 nm, whereas the direct band gap energy (EdEd) of CeO2 also decreased from 3.79 eV to 3.38 eV.