ZnS:Mn was produced in nanocrystalline form by a chemical method using polyvinylpyroledone as a chemical capping agent. Mn was stoichiometrically substituted for Zn in ZnS. The manganese (Mn) concentration was varied over its whole solid solution limit in ZnS, i.e., from 0 to 40%. In the high concentration regime this material formed may be thus written as nanocrystalline (Zn, Mn)S. The material formed is thus a wide gap diluted magnetic semiconductor. The characterized material was in powder form. X-ray diffraction was used to estimate the crystallite size and to confirm formation of the material in single phase. The average crystallite size obtained was about 2 nm. The material remained cubic over the whole Mn solid solution range. The room temperature photoluminescence (PL) when deconvoluted using a Gaussian fit showed two extra peaks in nanocrystalline ZnS:Mn when compared to pure nanocrystalline ZnS, which had only two peaks. Mn incorporation significantly enhanced the PL intensity in nanocrystalline ZnS:Mn (400–850 nm range) thereby suggesting Mn2+ induced PL. The red shift of the two new peaks with increase in Mn2+ concentration can be attributed to the change in band structure due to the formation of ZnS:Mn alloy. These extra peaks were due to (a) various Mn2+ transitions in the ZnS host, (b) related to S as the nearest neighbor of Mn2+ ion in the nanocrystallite (due to the high concentration of Mn2+), or (c) Mn–Mn interactions at high Mn concentrations. However, our prepared pure MnS samples did not show any photoluminescence at room temperature. So it is concluded that the observed PL is Mn2+ induced in the nanocrystalline ZnS host.

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To establish a reliable procedure for the characterization of luminescence from nanomaterials, the cathodoluminescence CL observation conditions, such as the packing density of particles and the electron beam energy for irradiation, were examined by using ZnO nanoparticles. The evolutions of the intensities and peak position with the accelerating voltage are strongly affected by the packing density of particles. For the low-density specimen, the band edge emission reaches a maximum at 4 kV where the excitation of each nanoparticle becomes the most effective. On the other hand, the position of band edge emission does not shift for low-density specimen while it changes for high-density specimen. Such artifact may bring serious modifications to the CL data. This work suggests that the specimen preparation and the optimum excitation conditions are the keys for the reliable CL characterization of nanomaterials.

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Here we report the preparation of nanocrystalline silica capped yttrium silicate doped with cerium and a study on its photoluminescence (PL) properties. The preparation method presented is simple and unique and can easily be scaled up for bulk production. The material shows blue luminescence at room temperature, and it is enhanced by a few orders of magnitude upon annealing. The PL intensities of these nanocrystalline samples are much stronger than similar bulk samples. The annealing temperatures required are much less than the bulk sample formation temperatures. Such annealing related PL enhancement is attributed to the formation of the optimum nanocrystalline size required for strong luminescence from nanoparticles due to the doped rare earth ions and quantum confinement related effects. It was also suggested that nano-Y 2 SiO 5 has a relatively more intense blue emission than the nano-Y 2 Si 2 O 7 phase. This is attributed to the position of the 5d level of Ce 3+ in the energy band.

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