Characterization and optical properties of Eu-doped cubic nano ceria synthesized by using the co-precipitation-hydrothermal route

Abstract

A series of nano ceria samples containing 0 to 2 mol% europium were synthesized following the co-precipitation hydrothermal technique. The X-ray diffraction patterns showed peaks corresponding to the fluorite structure of cubic ceria with shifting of the peak positions, but did not show any Eu-related peaks. The fourier transform infrared (FTIR) spectra of all the samples showed four bands that could be attributed to Ce-O stretching vibrations, formation of nano-crystalline particles, -HOH bending, and -OOH and -OH stretching vibrations. The Raman spectra of all the samples showed a sharp and intense Raman shift at around 460–462 cm⁻¹ corresponding to the triplydegenerate F _2g mode. The intensity of the Raman peaks showed variations in intensities. The transmission electron microscope (TEM) images of typical samples revealed that the shapes and the sizes of the particles were not much affected after Eu doping in the studied range though Eu doping resulted in agglomerations of nanoparticles. Broad absorption peaks centered at 292, 332, 336, 310, and 294 nm were observed for 0, 0.25, 0.5, 1, and 2 mol % Eu-doped ceria in the UVVis spectra with direct band gaps of 3.6, 2.75, 2.75, 2.75, and 3.25 eV, respectively. The smaller values of the indirect band gap indicated that Eu-doped nanoparticles were available to assist the indirect electron transition from the valence band to the conduction band. The emission peaks for the spectra obtained by exciting at 300 nm were observed at 355, 405, 396, 387, and 380 nm for pure ceria sample and 0.25, 0.5, 1, and 2 mol% Eu-doped samples, confirming the red shift in all the doped samples. The spectra for Eu-doped samples obtained by exciting at 500 nm showed three peaks in the orange-red region corresponding to the 5D₀ → 7F _j (j = 0 − 4) transitions of Eu³⁺.