Surface versus volume effects in luminescent ceria nanocrystals synthesized by an oil-in-water microemulsion method

Abstract

Pure and europium (Eu(3+)) doped cerium dioxide (CeO(2)) nanocrystals have been synthesized by a novel oil-in-water microemulsion reaction method under soft conditions. In-situ X-ray diffraction and RAMAN spectroscopy, high-resolution transmission electron microscopy, UV/Vis diffuse-reflectance and Fourier transform infrared spectroscopy as well as time-resolved photoluminescence spectroscopy were used to characterize the nanaocrystals. The as-synthesized powders are nanocrystalline and have a narrow size distribution centered on 3 nm and high surface area of ~250 m(2) g(-1). Only a small fraction of the europium ions substitutes for the bulk, cubic Ce(4+) sites in the europium-doped ceria nanocrystals. Upon calcination up to 1000 °C, a remarkable high surface area of ~120 m(2) g(-1) is preserved whereas an enrichment of the surface Ce(4+) relative to Ce(3+) ions and relative strong europium emission with a lifetime of ~1.8 ms and FWHM as narrow as 10 cm(-1) are measured. Under excitation into the UV and visible spectral range, the europium doped ceria nanocrystals display a variable emission spanning the orange-red wavelengths. The tunable emission is explained by the heterogeneous distribution of the europium dopants within the ceria nanocrystals coupled with the progressive diffusion of the europium ions from the surface to the inner ceria sites and the selective participation of the ceria host to the emission sensitization. Effects of the bulk-doping and impregnation with europium on the ceria host structure and optical properties are also discussed.

One‐Pot Synthesis of Mn‐Doped CeO2 Nanospheres for CO Oxidation

“…[21,[28][29][30] Figure 2 illustrates the contrastive Raman spectra of the pure, undoped CeO 2 sample ( -1 is related to the first order F 2g Raman active mode of the CeO 2 fluorite structure, which can be regarded as a symmetric breathing mode of the oxygen ions around each Ce 4+ cation. [31,32] The absence of the Mn-O characteristic peak (in the range 620-660 cm -1 ) is indicative of the formation of solid solutions as indicated by the XRD results. [14] However, in contrast with pure CeO 2 , slight shifts towards lower frequency and broadening of the F 2g Raman peaks of doped samples evidence local structure distortion on embedding manganese ions into the lattice sites of CeO 2 .…”

New Trends on the Synthesis of Inorganic Nanoparticles Using Microemulsions as Confined Reaction Media

“…In a more recent study by the same group (Tiseanu et al, 2011), Eu-doped luminescent CeO 2 nanocrystals were prepared by the same method. Several characterization techniques ( X-ray diffraction, RAMAN spectroscopy, UV-Vis diffuse-reflectance, FTIR as well as time-resolved photoluminescence spectroscopy) were used to characterize the nanocrystals, and it was shown that there was a surface enrichment of Eu 3+ , which diffused progressively to the inner Ceria sites upon calcination.…”

Defect Chemistry and Vacancy Concentration of Luminescent Europium Doped Ceria Nanoparticles by the Solvothermal Method

“…31,55 Figure 6a shows the excitation spectra for emission at 608 nm of undoped and europium doped CeO2…”

“…18 This property promotes charge transfer from oxygen ions through the lattice oxide and provides the material with high oxygen ion conductivity. 19 If energy is transmitted from this charge transfer state to lanthanide ions characteristic emissions are expected to be observed.…”