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Pure and Dy-doped ZnNb2O6 nanoparticles have been prepared by a sol−gel combustion method using citric acid as a fuel and complexing agent and nitrates as oxidants at a relatively low temperature as compared to solid-state reaction methods. X-ray diffraction patterns of the pure ZnNb2O6 samples show that the ZnNb2O6 nanoparticles exhibit an orthorhombic phase. Photoluminescence (PL) properties of all the undoped and Dy-doped samples are studied in detail. For the pure ZnNb2O6 samples, a strong blue emission band centered at 445 nm and two weak emission bands centered at 525 and 625 nm, respectively, can be observed. For Dy-doped ZnNb2O6 samples, the luminescence of Dy3+ is observed with the host blue emission remaining and the host emission intensity varying with the Dy-doping concentrations. This novel PL characteristic of the doped samples may be attributed to the energy transfer between Dy3+ and niobate groups (NbO6).

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YNbO 4 and YNbO 4 :RE (RE ) Er 3+ , Sm 3+ , Tb 3+ , and Tm 3+ ) nanophosphors have been prepared using a citrate-gel combustion procedure. The results of X-ray diffraction reveal that the YNbO 4 samples crystallized in both monoclinic and tetragonal phases in the investigated temperature range. The excitation spectra of the undoped YNbO 4 samples exhibit a red-shift as annealing temperature or time increases, and the emission spectra show a broadband around 400 nm, corresponding to the self-activated luminescence center of YNbO 4 . Upon UV excitation of the niobate host, characteristic emissions from f-f transitions of the RE ions were observed. The luminescence covers the blue (Tm 3+ ), green (Er 3+ , Tb 3+ ), and orange-red (Sm 3+ ). The mechanism of the energy transfer between the niobate host and the RE ions was deduced.

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Chalcopyrite CuInS2 is an important photovoltaic material. CuInS2 hollow nanospheres with diameters of 80−100 nm have been synthesized by a surfactant-assisted solution-chemical route. Structural characterization indicated that shells of the hollow spheres are composed of CuInS2 nanoparticles of about 10 nm in size. A vesicle-template mechanism was proposed to explain the formation process of the hollow structure, during which amorphous hollow structures are first formed on the surfactant template and then crystallize in the refluxing process.

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