Size-dependent optical properties of nanocrystalline CeO2 :Er obtained by combustion synthesis

Abstract

Nanocrystalline Er-doped CeO₂ phosphors with an average crystallite size of 18, 38, and 70 nm were prepared by glycine–nitrate solution combustion synthesis. The particle size of the resultant powders is tied up with the combustion flame temperature, which can be controlled by adjusting the ratio of glycine to nitrate. The microstructure and morphology of the CeO₂ :Er materials were investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM). It is found that nanocrystalline CeO₂ :Er is surrounded by amorphous phase, and that the area of the amorphous phase increases with the decrease of the particle size. The photoacoustic spectra (PAS) show the particle-size dependence of the optical properties. With the decrease of the particle size, a blue shift of the PAS absorption peak and an enhancement of the exciton absorption are observed, which result from a quantum size effect. The photoluminescence of the CeO₂ :Er materials was measured. When the nanoparticle size decreases, the red-to-green ratio of the Er³⁺ emission becomes high. This means that there is a stronger interaction and a more efficient energy transfer between the Er³⁺–Er³⁺ dopants in smaller CeO₂ :Er nanocrystals.