Effect of rare-earth oxide additives on transparency and fluorescence of a-SiAlON ceramics

Recently, novel transparent and fluorescent materials are in demand for various optical applications such as lasers, scintillators, and solid-state lighting. alpha-SiAlON, which has excellent thermal and mechanical properties, also exhibits photoluminescence depending on the stabilized doped rare-earth ions. Its transparency and fluorescence depend on the rare-earth oxide added as a raw material, particularly in conventional powder processing. In this study, we fabricated alpha-SiAlON ceramics by adding various rare-earth oxides to elucidate their effects on the transparency and fluorescence of these ceramics. High-transparency alpha-SiAlON ceramics were fabricated by adding rare-earth oxides whose rare-earth ions have small ionic radii: Y2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3. Because the fraction of alpha-SiAlON was high, the relative density was high, and the microstructure was composed of fine grains. In particular, alpha-SiAlON ceramics prepared by adding Ho2O3 showed lower light scattering than the other fabricated alpha-SiAlON ceramics because of the smaller alpha-SiAlON grains, resulting in higher in-line transmittance (48% at 600 nm). Furthermore, these transparent alpha-SiAlON ceramics exhibited fluorescence corresponding to the activated rare-earth ions: Ho3+, Er3+, Tm3+, and Yb3+ or Yb2+.