Photoluminescent and structural properties of ZnO containing Eu³⁺ using PEG as precursor

Abstract

Abstract ZnO powders containing different concentrations of Eu³⁺ synthetized using polyethylenoglycol (PEG) as precursor are reported. The viscous solutions were obtained and heated-treated at different temperatures to obtain materials in powder form in order to analyze the influence of temperature on photoluminescent and structural properties. The synthesis proposed in this paper enable the fabrication of the zinc oxide material containing Eu³⁺ with high relative concentrations. TG and DTA analyses allowed the behavior of the decomposition of precursors used in the synthesis to be observed. PEG used as precursor proved to be a very interesting molecule, producing materials with good photoluminescent properties. The structural characteristics of the material were evaluated by X-ray diffraction, followed by a Rietveld refinement. The results obtained show that is possible to incorporate Eu³⁺ in a ZnO host matrix with relatively high concentrations. The cell parameters showed minimal distortion and were independent of Eu³⁺ concentration. From calculation of the band gap, the difference of energy between HOMO and LUMO of 3.28 eV was determined which is in accordance with the literature. The presence of Eu³⁺ makes the material a red emitter and the color of emission is dependent on wavelength of excitation (294 or 463 nm). The excitation at 294 nm promotes the photoluminescence emission in the visible region with large band assigned to the defects present in the ZnO host matrix. However when the material is excited at 463 nm (exactly on Eu³⁺ energy level) bands with intense emission around 612 nm are observed and assigned to the hypersensitive intraconfigurational transition of Eu³⁺ and the large band below that wavelength it is observed. The presence of a large band emission when the samples are excited at 463 nm is an indication of the energy transfer from Eu³⁺ to the ZnO host matrix. The results obtained demonstrate that with this synthesis, the structural and photoluminescent properties of the product make it a potential candidate for applications in solar cells.