White light emission from spin coated Gd2O3:Dy nano phosphors synthesized using polyol technique.

Water dispersible Gd2O3:Dy3+ (2%) nanophosphors were synthesized through a facile polyol process and characterized by using X-ray diffraction (XRD), transmission electron microscopy (TEM), Dynamic Light Scattering (DLS) and photoluminescence (PL) spectrophotometry. The results of XRD, TEM and DLS show that resultant nanoparticles are single phasic and have spherical shape with 17 to 22% dispersibility. An efficient energy transfer was observed from host to the dopant ions. Characteristic blue and yellow emissions from Dy3+ ions were observed. The CIE coordinates of the nanophosphor lie in the white light region of the chromaticity diagram. Spin coating of the nanophosphor was done on quartz substrate. Bright white luminescence of this film was observed under ultraviolet light with lamda exc = 310 nm.

Nanocrystalline gadolinium doped ceria: combustion synthesis and electrical characterization.

Twenty mol% gadolinium doped ceria powders were prepared by citrate-nitrate combustion synthesis technique. Two different sources of cerium viz. cerium nitrate and ammonium ceric nitrate were used in different oxidant-to-fuel ratios. The crystallite size of the synthesized powders ranged 5-27 nm was obtained depending on the preparation conditions with average particle size in the range 0.64-1.26 microm. Although, the powders were found to be agglomerated in nature, these powders were highly sinter-active as they showed very high sintered density (> or = 95%) when sintered at 1250 degrees C having grain size in the range of 200-500 nm. The electrical conductivity was found to depend on the temperature with two distinct regimes at a transition point of 350 degrees C. The grain boundary showed a significant role in the total conductivity with its activation energy dependent on the material preparation conditions. The activation energy of total conduction was found to be significantly low (-0.5 eV) in the temperature range of 400-700 degrees C, this property is unique for application as an electrolyte for solid oxide fuel cell operating in the low temperature range. It was found that a fuel-deficient combustion reaction using cerium nitrate as the oxidant yielded the best quality powder which showed a maximum electrical conductivity of -1.74 x 10(-2) S/cm at 600 degrees C.

Nanocrystalline HoCrO4: facile synthesis and magnetic properties.

Nanocrystalline HoCrO4 powder was synthesized by a combustion technique using glycine and citric acid as the fuels in different oxidant-to-fuel ratios. Fuel-deficient glycine-nitrate combustion reaction resulted in zircon type HoCrO4 free from HoCrO3 phase. The crystallite size for the phase pure product after calcination at 575 degrees C in oxygen atmosphere was found to be 34 nm by X-ray line broadening. The TEM observations showed highly porous structure. Magnetic measurements reveal the ferromagnetic nature of HoCrO4 nano particles with Tc = 18 K. The compound shows high remanence of 30.4 emu x g(-1) and low coercivity of -0.0343 T.

Rare-earth doped gadolinia based phosphors for potential multicolor and white light emitting deep UV LEDs.

Gadolinium oxide host and europium/dysprosium/terbium doped gadolinium oxide nanoparticles were synthesized using the sonochemical technique. Gadolinium oxide nanocrystals were also co-doped with total 2 mol% of Eu(3+)/Dy(3+),Eu(3+)/Tb(3+),Dy(3+)/Tb(3+), and also Eu(3+)/Dy(3+)/Tb(3+) ions, by the same method. The nanoparticles obtained were characterized using powder x-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) techniques. The size of the particles ranged from 15 to 30 nm. The triple doped samples showed multicolor emission on single wavelength excitation. The photoluminescence results were correlated with the lifetime data to get an insight into the luminescence and energy transfer processes taking place in the system. On excitation at 247 nm, the novel nanocrystalline Gd(2)O(3):RE (RE = Dy, Tb) phosphor resulted in having very impressive CIE chromaticity coordinates of x = 0.315 and y = 0.316, and a correlated color temperature of 6508 K, which is very close to standard daylight.

Nano crystalline ceria-neodymia solid solutions by combustion route: effect of agglomeration on powder properties.

About 8 compositions in the system Ce(1-x)Nd(x)O(2-x/2) (0.0 < or = x < or = 0.50) were prepared by the combustion process using glycine as a fuel and corresponding metal nitrates as the oxidants. The oxidant-to-fuel ratio was taken as 1:1.0. The products were characterized by X-ray diffraction (XRD), surface area, scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering, sinterability etc. The crystallite size of powders, as obtained by the line broadening method, was typically in the range of 7 to 16 nm. The deagglomeration studies carried out showed that the average agglomerate size of these powders increases with increasing content of Nd in CeO2. The powders were sintered at 1200 degrees C to yield densities in the range of 80-95% of theoretical densities. This wide variation in the sintered density was explained based on the powder properties. An interesting observation was that the nature and size of the agglomerates plays an important role in governing properties such as sintered density and in turn ionic conductivity of nano ceramics.