Engineering Rare Earth Ion Doped Metal Oxide Core-Shell Nanostructures

Rare earth doped yttrium oxide (Y2O3) and lanthanum phosphate (LaPO4) core nanostructures were synthesized using either the molten salt method or the hydrothermal method, followed by the addition of a thickness-controlled shell layer by the sol-gel synthesis. The hydrothermal growth and dehydration process of Y(OH)3 nanotubes was studied in order to understand the formation process to scale up the synthesis for commercial applications. The synthesis process was probed using synchrotron in situ extended X-ray absorption fine structure spectroscopy and X-ray diffraction characterization methods for high resolution analysis. Both characterizations methods indicated the nanotubes were fully formed after a 7 hr hydrothermal reaction and a stable YOOH intermediate was formed between 300-400°C, after which the desired Y2O3 from is obtained.;With the ability to accurately control the morphology and architecture of the phosphor nanostructure, the electromagnetic interactions of the RE ions were probed using the luminescence spectrum. The Era3+ doped Y2O3 and Yb3+, Era3+ co-doped Y2O3 systems were studied to assess the effect of surface passivation using either an active or inert shell on the luminescence spectrum, emission lifetimes, and upconversion luminescence. A 5 nm Y 2O3 shell layer was shown to increase the crystal field splitting, visible through the Stark splitting, while simultaneously increasing the 4S3/2-4I15/2 emission lifetimes by up to 53% above that of the Er3+:Y2O3 core. Additionally, the shell layer reduced the upconversion photon requirement from 3 to 2, due to the excited state absorption probability being higher than the energy dissipation to phonons and surface hydroxyl groups. Furthermore, the blue Tm3+ upconversion emission spectrum was observed by selectively exciting the spatially controlled Yb3+ within the nanostructure using a 980 nm laser diode.;Finally, a core-multi-shell system was synthesized to generate white light from a multi-doped phosphor using a single excitation wavelength. The position of Eu3+, Dy3+, Tb3+, and Ce3+ were spatially controlled in a LaPO4 host lattice by the complex multi-shell structuring which serves to not only mitigate parasitic energy transfer events between the active ions but also promote the sensitization effect of Ce3+. In order to quantify the phosphor architectures, the CIE coordinates and lifetimes were measured. When excited with 365 nm photons, the optimum phosphor architecture, EulCe, Dy|Tb:LaPO 4, resulted in a CIE coordinates of (0.34, 0.35) and a 16 %, 31 %, and 36 % increase in lifetimes over the RE3+:LaPO4 reference phosphors, where RE= Eu, Dy, and Tb, respectively. By understanding the interatomic RE energy transfer events, it was possible to design a high quality, high efficiency white light phosphor, suitable for application in LED devices as a replacement for incandescent and fluorescent lighting.