Preparation and characterization of thin optically transparent alumina and Ce-doped alumina

Transparent and porous boehmite, gamma-Al2O3 (500degreesC) and theta-Al2O3 (900degrees and 1000degreesC) thin sheets (50-100 mum) have been prepared from boehmite sols. gamma-Al2O3 shows about 48% porosity and 292 m(2)/g surface area. On transformation from gamma-Al2O3 (500degreesC) to theta-Al2O3 (900degreesC), the porosity still remains high, i.e. similar to45%; however, the surface area becomes 138 m(2)/g. The porosity and surface area of theta-Al2O3 become about 41% and 97 m(2)/g respectively on further heating to 1000degreesC. A gradual increase of average pore radius during this thermal treatment suggests that coarsening of the pore occurred during the densification process. Both gamma-Al2O3 and theta-Al2O3 show high degree of transmission from UV to NIR wavelength region. Cerium exists in +4 oxidation state in the boehmite as well as in the gamma- and theta-Al2O3. The ultraviolet absorption edge of the alumina was tailored by varying the concentration of cerium.