Preparation and optical properties of transparent zirconia sol-gel materials

Both optical properties and morphology of zirconia hybrid sol-gel materials strongly depend on the addition of modifying agents like acetylacetone and acetic acid. Acetylacetone leads to the formation of yellow-brown complexes with high absorption, acetic acid / nitric acid addition results in transparent, colorless gels. The optical band gap (4.84 ± 0.29 eV) of zirconia gels obtained without protection agents is close to that of yttrium doped zirconia single crystals. Acetic acid / nitric acid and acetylacetone addition decrease the band gap down to 4.41 ± 0.185 eV and 2.97 ± 0.45 eV, respectively, due to complex formation with zirconium. Detailed UV/Vis/NIR analysis turns out to be a useful method for understanding the physical nature of processes, including complex forming modifying agents in sol-gel chemistry.