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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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