Sintering of a ZnO–SnO2
mixture under argon flow leads to the growth of microrods on the sample surface, which are
formed by oriented stacks of nanoplates. Energy dispersive spectroscopy and
cathodoluminescence (CL) in the scanning electron microscope show that the
stacks of nanoplates consist of Sn doped ZnO. The stacks of nanoplates have well
defined orientations relative to the growth axis of the rod. The formation of the
nanoplates, which is not observed when undoped ZnO is used in the same process, is
attributed to the stresses generated by the presence of Sn atoms in the rods.
W and W alloys containing 0.5 wt% Y 2 O 3 , x wt% Ti and (x wt% Ti + 0.5 wt% Y 2 O 3 ) have been prepared, x 2 or 4. Elemental powders were blended or ball milled, canned, degassed and finally consolidated by a two stage HIP process under a pressure of 195 MPa. It is found that Ti addition favours the densification attaining a fully dense material. XRD, SEM and EDX analyses of the material with Ti addition reveal the formation of a microstructure consisting of tungsten particles embedded in a W Ti matrix. The microhardness of these materials increased noticeably with the titanium content.
Rare-earth (RE) ions are widely investigated luminescent centers because their intraionic-4f transitions generate narrow and intense emission lines. In this work Eu doped ZnO nanoneedles have been grown, by a thermal evaporation-deposition method, and structural and luminescence characterization has been carried out. Mixtures of ZnO and Eu2O3 or of ZnS and Eu2O3 powders were used as precursors. Annealing of the compacted powder mixtures leads to the growth of nanoneedles and nanoneedle networks, as well as rods. EDS and CL measurements enable to detect the incorporation of Eu in these structures. The choice of precursor, ZnO-Eu2O3 or ZnS-Eu2O3 influences the morphology as well as the luminescence properties of the obtained nanostructures. In particular, while in the samples obtained from ZnO, the defect green luminescence band is practically absent, the band is present in the ZnO nanoneedles obtained from ZnS. Besides the broad deep level band, a series of well-separated narrow-peaks characteristic of the intrinsic red luminescence of Eu+3 ions are observed in all cases, whose relative intensities vary from one set of samples to the other. The results suggest that the Eu3+ ions have at least, two possible configurations in the ZnO lattice with different symmetry in the nanoneedles.
Al doped ZnO arrays of nanoplates and of ordered nanoneedles have been grown by a thermal evaporation-deposition method. The nanoplates, which have mainly triangular shape. Interpenetrating triangles and crossing of the triangles with other planar arrangements form a structure consisting of arrays of microboxes. The influence of Al on the luminescence of the nanostructures has been studied by cathodoluminescence ͑CL͒ in the scanning electron microscope. Intense CL emission from the internal faces of the microboxes is related to the presence of deep level defects.
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