Page 139 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Rare Earth Doped Yttrium Oxide Nanophosphors Synthesis and Engineering- Controllable Photoluminescence Properties
Figure 7.3 FTIR spectra of (a) the dried Y(OH)3 and Y(OH)3:5%Eu3+; (b) Y2O3 and Y2O3:5%Eu3+ nanoparticles annealed at 600 °C.
Figure 7.4(a-d) show TEM images of 5% Eu3+ doped yttria nanophosphors with heat treatment at temperature range of 600~1200 °C. It is seen that products are in nanoscale, with irregular shapes being aggregated together. Their size and size distributions undergo an apparent increasing trend with temperature (Supplementary Material Figure S1). This is due to the enhanced Ostwald ripening process at higher calcination temperature, where larger particles are more energetically stable than smaller ones. The result suggests that this technique is capable to produce nano-sized phosphors without any stabilizers or surfactants. A reasonable explanation is the mild hydrolyzing process induced by the plasma. In contrast to conventional wet chemistry methods by adding supersaturated alkali precipitants, hydroxyl radicals are smoothly released from water to homogenously form ultra-small sediments in a “bottom-up” manner, avoiding vigorous hydrolyzing reactions. Furthermore, the crystalline structure of nanophosphors heat-treated at 1200 °C is examined by SAED and HRTEM. The regular arrangement of the diffraction spots that forming concentric diffraction rings suggests their crystalline nature. Moreover, particles exhibit clear lattice fringes, with different crystal planes being observed. An estimation of the interplanar distance (d-spacing) of a typical nanoparticle by measuring the distance across 10 atomic planes deduces ~4.6 Å, a slightly larger than the (211) plane of yttria nanoparticle (~4.3 Å). This can be explained by the substitution of yttrium ions (r=0.89 Å) for larger europium ions (r=0.95 Å), which in turn, revealing that Eu3+ ions have been doped into the yttria lattice.14
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