2D- and 3D-Photoluminescence Imaging of Eu(Ⅲ) Embedded in CeO_2 Nanomatrix

摘要

2D- and 3D-photoluminescence characteristics of Eu(III) doped in CeO_2 nanoparticles were fully imaged for the first time. Their fundamental natures were also examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) crystallography, and UV-visible absorption spectroscopy. The magnetic dipole ~5D_0 → 7F_1 transition was dominated by an indirect transition associated with a O~(2-)-Ce~(4+) charge-transfer band of CeO_2. The electric dipole ~5D_0 → ~7F_2 transition was dominated by a direct transition of Eu(Ⅲ), indicating that Eu (Ⅲ) replaces Ce(Ⅳ) at octahedral sites (O_h and O) with and without an inversion center. Upon annealing, the photolumines-cence intensity caused by direct transition was dramatically decreased, whereas that induced by indirect transition was greatly enhanced. These findings indicate that charge transfer to the Eu(Ⅲ) at the octahedral (O_h) site with the inversion center is more efficient than that to the Eu(Ⅲ) site without an inversion center. The absolute quantum yield for the 10 mol% Eu(Ⅲ)-CeO_2 was found to be Φ= 0.007 at an excitation wavelength of 350 nm. The photoluminescence of Tb-doped CeO_2 was briefly discussed for comparison.