Influence of high-temperature oxidation on photoluminescent properties of white SiOC(–H) ceramics

• Oxidation resistance of SiOC(–H) ceramics strongly depends on the H/C ratio.
• At a high H/C ratio, blue PL rapidly disappears during oxidation.
• At a low H/C ratio, white PL gradually decreases during oxidation.
• Intensity of phosphorescence decreases at relatively low oxidation temperature.

SiOC(–H) ceramics were prepared by pyrolyzing densely cross-linked polysiloxane particles in hydrogen at temperatures of 800, 900 and 1100 °C. Thermogravimetric–differential thermal analysis (TG–DTA) curves of these SiOC(–H) ceramics in an air flow revealed that the oxidation resistance strongly depended on the decarbonization temperature. On the other hand, these decarbonized samples were oxidized in dry air flow at temperatures of 300, 500, 700, 1000 and 1200 °C. After the oxidation in air, photoluminescent (PL) spectra and Fourier transform infrared (FTIR) spectra of the oxidized samples were investigated. In partly organic SiOC(–H) ceramics with high H/C ratios, the intensity of blue PL simultaneously decreased with rapid oxidation. Residual weak PL peaks are probably assigned to defects in silica formed on particle surfaces. In dense SiOC(–H) ceramics with a relatively low H/C ratio, the intensity of white PL gradually decreased with moderate oxidation and the PL peak position shifted to longer wavelengths. Intensity of phosphorescence of the dense SiOC(–H) ceramics was also weakened after oxidation. The decrease of phosphorescence intensity, however, began at a rather low temperature range as compared with that of the apparent PL.