Mechanochemical and Combustion Syntheses of Cerium-Doped Lutetium Oxyorthosilicate Powders and Preliminary Studies into the Syntheses of Optically-Active Beta-Germanium(IV) Oxide and Alpha-Quartz Nanoparticles

Abstract

Lu2SiO5:Ce powders were produced using solvent-free mechanochemistry. The Burgio-Rojac model for the planetary ball mill was used to conduct a parametric study of this synthesis, investigating the effect of varying the powder mass, the vial and ball density, the number of balls, the diameter of the balls, and the rotation rate of the mill on reaction time. The influence of additives was researched with Zn possibly leading to increased reduction of Ce4+ to Ce3+ and with various solvents hindering or preventing Lu2SiO5:Ce production. The solution and gel combustion syntheses of Lu2SiO5:Ce powders were executed using the fuels urea and hexamethylenetetramine both individually and as a mixture. The mixed-fuel solution combustion method successfully produced LSO:Ce powder with excellent replicability. This method produced LSO:Ce powders with a combination of the P 1 21/c 1and C 1 2/c 1 space groups, which were compared to mechanochemically-produce LSO:Ce powders with C 1 2/c 1 symmetry. Lu2SiO5:Ce powders produced by each method were sintered using either a microwave or a furnace. While furnace sintering increased intensity in their photoluminescence excitation and emission spectra, the intensity was decreased with microwave sintering. By furnace sintering the previously microwaved-sintered powder in air, it was determined that oxygen vacancies created during microwave sintering caused the loss of photoluminescence intensities. Preliminary studies were conducted to synthesize optically-active α[alpha]-quartz nanoparticles using optically-active β[beta]-GeO2 nanoparticles as a template. Templating optical activity in β[beta]-GeO2 nanoparticles using L-lysine and (R)-(+)-1,2-diaminopropane as templating agents was attempted. No optical activity was observed in polarimetry and circular dichroism measurements, which was most likely due to insufficient capping agent adsorption. Rac-β[beta]-GeO2 nanoparticles were used to attempt to template α[alpha]-quartz at room temperature as well as when heated in NaOH, NH4OH, Ba(OH)2, and CsOH solutions. α[alpha]-Quartz did not form in any powders although the silica may have dissolved during the heating