Effects of Eu3+ concentration on structural, optical and vibrational properties of multifunctional Ce(1-x)Eu(x)O2-delta) nanoparticles synthesized by thermolysis of 2,4-pentanedione complexes.

The 5-10 nm Ce(1-x)Eu(x)O(2-delta) (0 < or = x < or = 0.30) nanoparticles with fluorite structure were synthesized by thermal decomposition of Eu- and Ce-2,4-pentanedione complexes mixtures. X-ray line broadening analysis of mixed samples Ce(1-x)Eu(x)O(2-delta) (0.05 < or = x < or = 0.30) showed that the crystallite size was lower and root mean square strain higher than in pure ceria. However, within mixed samples Ce(1-x)Eu(x)O(2-delta) (0.05 < or = x < or = 0.30) crystallite size and root mean square strain were independent of Eu3+ concentration. Raman spectroscopy results indicated that europium ions yield disorder by breaking the phonon propagation and therefore making the non-centre Brillouin zone modes Raman active. The absorption bands in the spectra of mixed oxides were blue-shifted in comparison to pure CeO(2-delta) nanopowder. The samples show red emission typical for Eu ions. The biggest photoluminescent intensity was observed for the highest Eu3+ concentration (x = 0.30) and further enhanced with the increase in crystallinity.

Enhanced structural and magnetic properties of fcc colloidal crystals of cobalt nanoparticles.

We report the elaboration of supercrystals made up of dodecanoic acid-coated 8.1 nm-Co nanocrystals with controlled supercrystallinity, morphology and magnetic properties. Supercrystal growth is controlled using a solvent-mediated ligand-ligand interaction strategy. Either face-centered cubic supercrystalline films or single colloidal crystals composed of cobalt nanocrystals are obtained. The change in supercrystal morphology is explained by Flory-type solvation theory using Hansen solubility colloidal parameters. The use of the same batch of Co nanocrystals for the fabrication of supercrystalline films and colloidal crystals enables accurate comparative structural and magnetic studies using (high-resolution) transmission electron microscopy, field emission gun scanning electron microscopy, grazing incidence small-angle X-ray scattering and vibrating sample magnetometry. The nearest neighbor distance between nanoparticles is interpreted using theoretical models proposed in the literature. We evidence the increase in both geometric anisotropy and magnetic dipolar interactions for colloidal crystals compared to supercrystalline films.

Phonon confinement in SiC nanocrystals: comparison of the size determination using transmission electron microscopy and Raman spectroscopy.

Silicon carbide fibers of different generation/processing routes (NLM-Nicalon and Tyranno SA3) were thermally treated to trigger the growth of nanocrystals, which were analyzed using Raman spectroscopy and transmission electron microscopy (TEM). The nanocrystals were also aged in molten sodium nitrate to investigate their reactivity. The spatial correlation model has been used to model the Raman spectra and extract accurate and statistical information on the nanocrystallites' structure and dimension. For the NLM fibers, an average size of 2.5 to 7.0 nm was calculated, which was in good agreement with TEM observations. For the Tyranno SA3 fiber, despite the heavily faulted stacking sequence, the Raman peaks remained sharp, indicating that the crystallite dimension calculated from the Raman spectra is only dependent on the actual size of the nanocrystals and is not affected by the sequence of the stacking faults.

CdSxSe1-x quantum dots as colouring agents of Art Nouveau and contemporary stained glass: a combined transmission electron microscopy and Raman study.

The use of cadmium chalchogenide nanoprecipitates to obtain brightly coloured glasses enormously expanded by the beginning of the twentieth century, when the production of cadmium-based pigments was already well established. Six historical stained glass pieces produced between the late 1920s and modern days have been investigated in order to delineate the average size and the elemental composition of the nanocrystals. As non-invasive conditions are now mandatory when considering objects belonging to cultural heritage, Raman spectroscopy is used to measure the (average) elemental composition of the nanoparticles. Zinc substitution is also detected by the shifting of the Raman peak position. Moreover, a tentative evaluation of size distribution and crystallinity of the nanoparticles has been performed considering those parameters that are mainly influenced by the disorder of the system, such as Raman band width, surface phonons and the ratio between second and first order band intensities. A confirmation of the above-mentioned conclusion is searched by means of transmission electron microscopy (TEM) and local elemental analysis. Raman investigations allowed identifying a different and more pronounced disorder characterizing the oldest glasses, also verified by TEM observations, suggesting a different manufacture.This article is part of the themed issue 'Raman spectroscopy in art and archaeology'.

Lattice distortions, magnetoresistance and hopping conductivity in LaMnO(3+δ).

Structural and transport properties of ceramic LaMnO(3+δ) are investigated for δ = 0-0.154. According to x-ray diffraction measurements at room temperature the crystal structure of this compound varies from orthorhombic (Pbnm) for δ = 0 to rhombohedrally distorted cubic (Pm3m) for δ = 0.065-0.112 and to rhombohedral ([Formula: see text]) crystal symmetry for δ = 0.125-0.154. These structural modifications are confirmed by the Raman micro-spectroscopy measurements. The resistivity displays in the range δ = 0-0.154 an activated behaviour both above and below the paramagnetic (PM) to ferromagnetic transition temperature, T(C). In the field of 8 T the relative magnetoresistance, Δρ(B)/ρ(0), reaches at δ = 0.154 the values of -88% near T(C) and -98% at [Formula: see text] K. The resistivity of the PM phase of LaMnO(3+δ) with δ = 0.100-0.154 satisfies the Shklovskii-Efros-like variable-range hopping (VRH) conductivity law between [Formula: see text] K and the VRH onset temperature [Formula: see text] K. The resistivity is governed by a complex energy dependence of the density of the localized states near the Fermi level, comprising a soft Coulomb gap [Formula: see text] eV and a rigid gap [Formula: see text] eV, the latter being connected to formation of small polarons.

Portuguese tin-glazed earthenware from the 17th century. Part 1: pigments and glazes characterization.

Two sherds representative of the Portuguese faience production of the first and second halves of the 17th century were studied carefully with the use of non-invasive spectroscopies, namely: Ground State Diffuse Reflectance Absorption (GSDR), micro-Raman, Fourier-Transform Infrared (FT-IR), Laser Induced Luminescence (LIL) and Proton Induced X-ray (PIXE). These results were compared with the ones obtained for a Chinese Ming porcelain, Wanli period (16th/beginning of the 17th centuries), which served as an influence for the initial Lisbon's faience production. By combining information of the different non-destructive spectroscopic techniques used in this work, it was possible to conclude that: Co(3)O(4) (Co II and Co III) can be found in the silicate matrix and is the blue pigment in the "Especieiro" sample (1st half of the 17th C.). Cobalt olivine silicate (Co(2)SiO(4), Co II only) was clearly identified as the blue pigment in "Aranhões" sample (2nd half of the 17th C.) - 824 cm(-1) band in the micro-Raman-spectrum. Cobalt aluminate (CoAl(2)O(4), Co II only) is the blue pigment in the Wanli plate - 203 and 512 cm(-1) bands in the micro-Raman spectrum. The blue pigment in the 1st half 17th century of Lisbon's production was obtained by addition of a cobalt ore in low concentrations, which gives no specific Raman signature, because of complete dissolution in the glass. However, in most cases of the 2nd half 17th century, the Raman signature was quite evident, from a cobalt silicate. These findings point to the use of higher temperature kilns in the second case.