Structure and luminescence properties of Eu~(3+) doped TiO_2 nanocrystals and prolate nanospheroids synthesized by the hydrothermal processing

摘要

We report on a new approach to the synthesis of Eu~(3+) doped TiO_2 nanocrystals and prolate nanospheroids. They were synthesized by shape transformation of hydrothermally treated titania nanotubes at different pH and in the presence of Eu~(3+) ions. The use of nanotubes as a precursor to the synthesis of Eu~(3+) doped TiO_2 nanocrystals and prolate nanospheroids opens the possibility of overcoming the problems related to molecular precursors. The shapes and sizes of the nanotubes, Eu~(3+) doped TiO_2 nanocrystals and prolate nanospheroids were characterized by transmission electron microscopy (TEM) technique. Crystal structures of the resultant powders were investigated by X-ray diffraction (XRD) analysis. The percentage ratio of Eu~(3+) to Ti~(4+) ions in doped nanocrystals was determined using inductively coupled plasma atomic emission spectroscopy. The optical characterization was done by using fluorescence and ultraviolet-visible reflection spectroscopies. An average size of faceted Eu~(3+) doped TiO_2 nanocrystals was 13 nm. The lateral dimensions of Eu~(3+) doped TiO_2 prolate nanospheroids varied from 14 to 20 nm, while the length varied from 40 to 80 nm, depending on precursor concentrations. The XRD patterns revealed the homogeneous anatase crystal phase of Eu~(3+) doped TiO_2 nanocrystals and prolate nanospheroids independently of the amount of dopant. A postsynthetic treatment (filtration or dialysis) was applied on the dispersions of the doped nanoparticles in order to study the influence of the dopant position on photoluminescence (PL) spectra. In the red spectral region, room temperature PL signals associated with ~5D_0 -> ~7F_j (J = 1-4) transitions of Eu~(3+) were observed in all samples. The increased contribution of dopants from the interior region of dialyzed nanocrystals to photoluminescence was confirmed by the increase of R value.