| Rare earth doped yttria nanoparticles were synthesized with a pulsed laser ablation technique. The effects of dopant concentration, starting materials, and post-ablation processing on the luminescent and structural properties were investigated. Increasing the amount of Tb in the yttria particles from 5% to 10% decreased the luminescence, contrary to what would be expected if more luminescent species (Tb3+ ions) were being added. However, using Tb2O3 instead of Tb4O 7 as the starting material did slightly increase the luminescence intensity of the Tb3+ emission. X-ray diffraction showed that the Tb:Y 2O3 samples were a mixture of the monoclinic Y2O 3 and anorthic TbO1.81 crystal structures. For the Eu:Y 2O3 nanoparticles, annealing the powder after the ablation synthesis improved the crystallinity of the particles, decreased the luminescence emission associated with Eu3+ in a monoclinic crystal structure and increased the emission associated with the cubic structure.; Rare earth oxide (Ho2O3, Er2O3 , Tm2O3, Yb2O3) nanoparticles were synthesized in two crystal structures through a combustion process. The temperature of the hydrogen flame, regulated by the composition of the supporting gas, determined the phase of the materials; higher flame temperature produced monoclinic rare earth oxide particles, and lower temperature produced cubic particles. The set of eight rare earth oxide nanoparticles---four different compositions, each in two phases---were examined with transmission electron microscopy, electron energy loss spectroscopy (EELS), and x-ray absorption spectroscopy (XAS). The EELS and XAS oxygen K edges for the sesquioxides in both phases were systematically analyzed. This work presents the first EELS and XAS study of the uncommon monoclinic phase in these materials and the first systematic comparative study between the monoclinic and cubic phases across a range of rare earth sesquioxides. For both phases, the usual double-peak structure of the oxygen K edge typically seen for oxygen atoms tetrahedrally surrounded by metal atoms was observed, but the details of the near edge structure to differ between the two phases. These results indicate a greater peak separation for the cubic than for the monoclinic phase. A trend of increasing peak separation with increasing atomic number was also noted for both phases in the series. |
