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A study used multinuclear solid-state NMR spectroscopy and powder X-ray diffraction (XRD) experiments to characterize a series of pure and lanthanide-doped La[F.sub.3] nanoparticles (NPs) that are capped with di-n-octadectyldithiophosphate ligands, as well as correlated bulk microcrystalline materials. The results reveal that [super 19]F-[super 31]P cross-polarization (CP)/magic-angle spinning (MAS) and [super 1]H MAS experiments have shown that ligands are coordinated to the NP surface.

Present study has been carried out to develop a facile synthetic methodology for preparing single phase monoclinic and triclinic forms of GdBO3, a potential phosphor material. This is achieved by varying annealing temperatures and annealing steps. Detailed structural studies, using X‐ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopic techniques confirmed that, Gd3+‐boric acid complexes formed initially at low temperatures (300 °C or less) get converted to monoclinic and triclinic forms of GdBO3 depending upon annealing temperatures, annealing steps and heating rates. Multiple steps with slow heating rates (∼3 °C/min) lead to the formation of single phase triclinic form of GdBO3. Two step heating with relatively faster heating rates (5 °C/min and above) results in single phase monoclinic GdBO3. FTIR and Raman studies also confirmed that boron exists only as BO4 structural units (in the form of B3O93− rings) in monoclinic GdBO3 and as BO3 structural units in triclinic GdBO3. Luminescence studies carried out with Eu3+ as a probe species confirmed more covalent nature around Eu3+/Gd3+ ions with improved red colour emission from triclinic form of GdBO3 compared to the monoclinic form. [ABSTRACT FROM AUTHOR]

Barium sodium borosilicate glasses containing different amounts of uranium oxides were prepared by conventional melt quench method and investigated for their structural aspects by 29 Si and 11B MAS NMR technique combined with steady-state luminescence and lifetime measurements. Based on MAS NMR studies, it is confirmed that uranium ions act as network modifier up to 15 wt% and beyond which a separate uranium containing phase is formed. From the luminescence studies, it is inferred that uranyl species is in a highly distorted environment. For more than 15 wt% uranium oxide incorporation, weaker U-O-U linkages are formed at the expense stronger U-O-Si/B linkages, as suggested by the excited state lifetime value of the uranyl species as well as red shift in emission peak maximum. For glass samples containing more than 25 wt% uranium oxides, crystalline barium uranium silicate gets phase separated from glass matrix as confirmed by XRD studies. [ABSTRACT FROM AUTHOR]

BaTiO3 and BaSnO3 samples doped with Eu3+ ions were prepared using glycine-nitrate gel combustion method. Relative intensities and line shapes of magnetic dipole allowed 5D0 → 7F1 and electric dipole allowed 5D0 → 7F2 transitions of Eu3+ from the hosts, BaTiO3 and BaSnO3, are significantly different. Based on detailed structural investigations, it is confirmed that synthesized BaTiO3 sample is tetragonal with no center of symmetry around Ba2+ ions. Unlike this BaSnO3 is cubic with centrosymmetric Ba2+ site. From X-ray diffraction and experimentally obtained Judd-Ofelt parameters (Ω2 and Ω4 values), it is confirmed that in BaTiO3 there is a decrease in the average Ba- O and Ba- Ba distances compared with that in BaSnO3. This leads to higher Eu- O bond polarizability and adds to the distortion in its environment around Eu3+ in BaTiO3: Eu compared with BaSnO3: Eu. This is responsible for the observed difference in the luminescence properties. [ABSTRACT FROM AUTHOR]

The structural and photoluminescence properties of Eu3+-doped Y2Sn2O7 nanoparticles have been systematically studied as a function of heat treatment temperature. Crystalline Y2Sn2O7:Eu nanoparticles with sizes in the range of 2-5 nm were prepared at the relatively low temperature of 700 °C. Based on the Rietveld refinement of powder X-ray diffraction patterns, it was confirmed that the YO8/EuO8 polyhedra in the Y2Sn2O7:Eu lattice become more symmetric as the annealing temperature increases. The extent of distortion of the YO8/EuO8 polyhedra is reflected in the luminescence parameters Ω2 and Ω4, which are a measure of the polarizability of Y-O and Eu-O bonds in the lattice. There are a significant number of surface Eu3+ ions in the nanoparticles annealed at 700 °C and the emission intensities of the Eu3+ ions in the nanoparticles are mainly decided by the surface Eu3+ ions, the concentration of which decreases with increasing temperature. Incorporation of the nanoparticles in a poly(methyl methacrylate) (PMMA) matrix leads to a decrease in the 5D0 lifetime and this has been attributed to the quenching of the excited states of surface Eu3+ ions through the vibrations of different structural units in PMMA. [ABSTRACT FROM AUTHOR]

GaPO4 nanoparticles having hexagonal structure with different amounts of Eu3+ ions were prepared at 130°C based on precipitation method in glycerol medium. The interaction between GaPO4 nanoparticles and Eu3+ ions has been investigated using Eu3+ luminescence and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. Based on these studies, it is established that Eu3+ ions up to 2.5 at.% replace the protons of the hydroxyl groups attached on Ga3+ ions present on the surface of the nanoparticles and above 2.5 at.%, a separate EuPO4 phase is formed. The anisotropy parameters derived from the side band intensities of the 31P MAS NMR patterns from these samples confirmed the surface ion exchange at low Eu3+ concentration (2.5 at.%) and EuPO4 phase formation at high Eu3+ concentration (5 at.% and more). The increase in anisotropy at high Eu3+ contents has been attributed to the presence of paramagnetic EuPO4 phase. [ABSTRACT FROM AUTHOR]

Nanoparticles of Eu3+-doped BaTiO3 having a hexagonal structure, which is a thermodynamically stable phase above 1432°C, have been prepared at a low temperature of 110°C based on the coprecipitation of Ti4+, Ba2+, and Eu3+ in ethylene glycol medium by adding urea. Based on differential thermal analysis studies, it is inferred that the as-prepared hexagonal phase of BaTiO3:Eu3+ is unstable and decomposes to the anatase form of TiO2 and barium carbonate above 420°C. Luminescence properties of the hexagonal form of BaTiO3:Eu3+ nanoparticles have been compared with cubic BaTiO3:Eu3+ nanoparticles prepared by the combustion method. Based on the detailed luminescence studies of Eu3+ in both cubic and hexagonal form of BaTiO3 samples, it is inferred that Eu3+ ions mainly occupy the Ti4+ sites in hexagonal BaTiO3 and both Ba2+ and Ti4+ sites in cubic BaTiO3. A comparison of the luminescence properties of Eu31 in hexagonal and cubic form of BaTiO3 suggested that there is increased distortion around Eu3+ in hexagonal BaTiO3 phase compared with cubic BaTiO3 phase, and this has been explained in terms of the distorted environment created around larger ionic radii Eu3+ ions occupying the smaller ionic radii Ti4+ site. There is a significant difference in the decay constant for 5D0 level of Eu3+ for these two forms of BaTiO3:Eu31 nanoparticles. [ABSTRACT FROM AUTHOR]

119Sn and 29Si solid-state nuclear magnetic resonance studies on lead silicate glasses containing different amounts of SnO2 confirmed that tin exists in the glass as distorted SnO6 polyhedra and there is no direct interaction between tin and silicon structural units. Transmission electron microscopic studies have established that tin structural units are uniformly distributed in the glass. Significant changes in the values of glass transition temperature, microhardness, and thermal expansion coefficient with SnO2 incorporation into the glass have been attributed to the increased rigidity of the glass network brought about by the replacement of weaker Pb–O linkages with stronger Sn–O linkages. [ABSTRACT FROM AUTHOR]

BaTiO3 and BaSnO3 samples doped with Eu3+ ions were prepared using glycine-nitrate gel combustion method. Relative intensities and line shapes of magnetic dipole allowed 5D0 → 7F1 and electric dipole allowed 5D0 → 7F2 transitions of Eu3+ from the hosts, BaTiO3 and BaSnO3, are significantly different. Based on detailed structural investigations, it is confirmed that synthesized BaTiO3 sample is tetragonal with no center of symmetry around Ba2+ ions. Unlike this BaSnO3 is cubic with centrosymmetric Ba2+ site. From X-ray diffraction and experimentally obtained Judd-Ofelt parameters (Ω2 and Ω4 values), it is confirmed that in BaTiO3 there is a decrease in the average Ba- O and Ba- Ba distances compared with that in BaSnO3. This leads to higher Eu- O bond polarizability and adds to the distortion in its environment around Eu3+ in BaTiO3: Eu compared with BaSnO3: Eu. This is responsible for the observed difference in the luminescence properties. [ABSTRACT FROM AUTHOR]

Bright blue-light emission at 410 nm is observed from Mg(2+)-doped GaN nanoparticles prepared by the nitridation of Ga(2)MgO(4) nanoparticles at 950 degrees C. The sintering of these nanoparticles during high-temperature nitridation was prevented by mixing the Ga(2)MgO(4) precursor nanoparticles with La(2)O(3) as an inert matrix before the nitridation process. The Mg(2+)-doped GaN nanoparticles were isolated from the matrix by etching with 10 % nitric acid. The Mg(2+)-doped GaN nanoparticles were characterized by photoluminescence, atomic force microscopy, X-ray diffraction, and IR analyses.