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Luminescent materials have found a wide variety of applications as phosphors for fluorescent lighting, display devices, X-ray monitoring and imaging, scintillators, and biomedical imaging. Indeed, the research in nanosciencehasbeen especially dedicated to the development of synthesis routes with the ability to synthetizenew material structures for industrial applications [1]. Fervent research in nanostructured materials has resulted in the development of novel synthetic methods to prepare pure and doped luminescent materials, and strategies to control the incorporation of dopant ions in nanoparticles. Hafnium oxide (HfO2) is considered as an attractive material because of its excellent physical and chemical properties, such as its high dielectric constant and insulating characteristics, which allow its application as a dielectric material with relatively high refractive index and wide band gap, as well in the field of optical coatings and next generation metal-oxide semiconductor devices. Moreover in recent investigations, nanometric hafnia when properly doped by rare earths (RE) ions has been also considered for optical applications [2]. Given the importance of HfO2 as host material for RE, its intrinsic optical response is also worth of investigation. In this work, we propose the study of the luminescent properties of undoped HfO2nanoparticles (NPs), achieved through a non-aqueous sol-gel process. The optical properties were studied by photo- and radio-luminescence considering the effect ofthe size and of the crystal phase. A broad composite emission was observed in the visible range, potentially correlated to intrinsic surface defects. A spectral analysis was performed, and the luminescence efficiency was compared to that of standard luminescent materials. Our studies reveal that HfO2 nanopowders may represent an interesting system in both phosphor technology and scintillation applications.

Silica–natural rubber nanocomposites were obtained through a novel non-aqueous in situ sol–gel synthesis, producing the amount of water necessary to induce the hydrolysis and condensation of a tetraethoxysilane precursor by esterification of formic acid with ethanol. The method allows the synthesis of low hydrophilic silica nanoparticles with ethoxy groups linked to the silica surface which enable the filler to be more dispersible in the hydrophobic rubber. Thus, high loaded silica composites (75 phr, parts per hundred rubber) were obtained without using any coupling agent. Transmission Electron Microscopy (TEM) showed that the silica nanoparticles are surrounded by rubber layers, which lower the direct interparticle contact in the filler–filler interaction. At the lowest silica loading (up to 30 phr) silica particles are isolated in rubber and only at a large amount of filler (>60 phr) the interparticle distances decrease and a continuous percolative network, connected by thin polymer films, forms throughout the matrix. The dynamic-mechanical properties confirm that the strong reinforcement of the rubber composites is related to the network formation at high loading. Both the improvement of the particle dispersion and the enhancement of the silica loading are peculiar to the non-aqueous synthesis approach, making the method potentially interesting for the production of high-loaded silica–polymer nanocomposites.

In this work a strategy for the control of structure and optical properties of inorganic luminescent oxide-based nanoparticles is presented. The nonaqueous sol-gel route is found to be suitable for the synthesis of hafnia nanoparticles and their doping with rare earths (RE) ions, which gives rise to their luminescence either under UV and X-ray irradiation. Moreover, we have revealed the capability of the technique to achieve the low-temperature stabilization of the cubic phase through the effective incorporation of trivalent RE ions into the crystal lattice. Particular attention has been paid to doping with europium, causing a red luminescence, and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol %, for either Lu3+ or Eu3+. The optical properties of the nanopowders were investigated by room temperature radio- and photoluminescence experiments. Specific features of Eu3+ luminescence sensitive to the local crystal field were employed for probing the lattice modifications at the atomic scale. Moreover, we detected an intrinsic blue emission, allowing for a luminescence color switch depending on excitation wavelength in the UV region. We also demonstrate the possibility of changing the emission spectrum by multiple RE doping in minor concentration, while deputing the cubic phase stabilization to a larger concentration of optically inactive Lu3+ ions. The peculiar properties arising from the solvothermal nonaqueous synthesis here used are described through the comparison with thermally treated powders. © 2013 American Chemical Society.

A time-dependent study on the formation of LiFePO 4 with olivine-type structure is presented. The material is synthesized through a non-aqueous route in benzyl alcohol assisted by microwave radiation. The LiFePO 4 forms with an anisotropic morphology of microscale stick-like particles. The detailed structure of these particles and their evolution with reaction time is revealed by transmission electron microscopy; a 3D reconstruction of a particle by electron tomography provides insight into the formation mechanism of these sticks. Without applying a thermal post-annealing treatment or a carbon coating, the electrochemical behavior of the LiFePO 4 microsticks is assessed for the preparation of cathodes in lithium-ion batteries. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.