Egg white synthesis and photoluminescence of platelike clusters of CeO2 nanoparticles

This paper reports the synthesis of platelike CeO2 nanoparticles by a simple, cost-effective, and environmentally friendly method using cerium(III) acetate hydrate and freshly extracted egg white (ovalbumin) in an aqueous medium. A platelike structure of CeO2 nanoparticles having the particle size of 6-30 nm was obtained by calcining the precursors in air at 400, 500, and 600 degrees C, for 2 h. Results from XRD, Raman spectroscopy, and SAED analysis indicated that the synthesized CeO2 nanoparticles have the fluorite structure of the bulk CeO2. All samples show a strong UV-vis absorption below 400 nm (3.10 eV) with a well-defined absorbance peak at around 284 nm (4.37 eV). The estimated direct band gaps are 3.61, 3.59, and 3.57 eV for the samples calcined at 400, 500, and 600 degrees C, respectively. These band gaps are 0.42, 0.40, and 0.38 eV higher than that of bulk CeO2, indicating the quantum confinement effect of the nanosize particles. The 400 and 500 degrees C calcined samples exhibited similar emission peaks of room-temperature photoluminescence. However, the sample calcined at 600 degrees C exhibited the strongest UV emission band at 392 nm (3.17 eV) because of its better-defined crystallinity compared to the other two samples calcined at 400 and 500 degrees C.