Layered Rare-Earth Hydroxide Nanosheets Of The Y/Eu Binary System:Low-Temperature And One-Step Synthesis,Interlayer Anion Exchange, Thermal Decomposition,and Their Oxide Materials Of Optical Functionality

This dissertation focuses on the studies of nitrate-type layered rare-earth hydroxides (LRHs), including low-temperature synthesis, interlayer anion exchange, structure characterization, and optical functionality explorations. Thermal decomposition behavior of the NO3--LLnH, SO42- -LLnH and F- -LLnH was studied in detail, and the phase, morphology evolutions and luminescence properties upon calcination in the temperature range 500-1100 ? were also investigated. The transparent ceramics were prepared using the oxides nano-powders calcined from the precursors synthesized via low-temperature precipitation. Crystal structures and physical properties of the materials are investigated in detail by the combined techniques of XRD, DTA/TG, FT-IR, FE-SEM, TEM, and PLE/PL spectroscopies.Ultra-thin (3-5 nm thick) LLnH (Ln=Y and Y0.95Eu0.05) nanosheets were successfully synthesized in one step via low-temperature (4-5?) chemical precipitation using ammonium hydroxide as precipitant. In situ and complete exchange of the interlayer NO3- with SO42- and F" were achieved by adding a proper amount of (NH4)2SC4 and NH4F solution into the suspensions of LRHs formed in a very short time, respectively. Calcining NO3- -LLnH at 600 ? and SO42- -LLnH at 1000? respectively both yield -60 nm single crystals of oxides. However, the resultant phosphors of Y2O3:Eu3+ calcined from NO3- -LLnH exhibit higher red emission intensity. The exchange of interlayer NO3- with F- induces a shrink of interlayer distance (c/2) manily due to the replacement of interlayer NO3- and part replacement of OH-in host layer by F-, but no obvious variations can be observed for the particle moophology. The F- -LLnH precursor decompose to (Y0.95Eu0.05)203 at 1100? via the intermediate phases (Y0.95Eu0.05)2O2.5F (at 6008) and mixture of (Y0.95Eu0.05)203 and (Y0.95Eu0.05)OF (at 750?) respectively. Enhanced photoluminescence intensity and decreased fluorescence lifetime can be observed for above oxides derived from the precursors with higher fluoride content. The transparent ceramic, possessing an average density of 5.018 g·cm-3 and a relative density of 99.7%, was prepared by pressure forming, isostatic cool pressing, presintering at 1300?, and sintering in vacuum at 1700?, using the obtained nano-powders as starting materials. In-line transmittance of the transparent ceramic in visible and near infrared regions is 25-40% and 54-67% respectively. Compared to Y2O3:Eu3+ powder, the Y2O5:Eu3+ transparent ceramic exhibit a higher red emission at 616 nm.