Coloration of Ti-doped sapphire grown by the Flame-Fusion Method

• Coloration of Ti-doped sapphire grown by the Flame-Fusion Method was examined.
• By UV irradiation, TiAlIV+ changed into TiAlIII× and hole (h+).
• The hole was trapped in VAl3−, and the resultant color center caused brown coloration.
• (Ti–Fe) and (Ti–Mg) co-doping was affected to prevent the coloration by UV.

Coloration of Ti-doped sapphire grown by the Flame-Fusion Method was examined here in detail. The as-grown sapphire was slightly colored with pink caused by Ti3+. After annealing in the air, the pink color faded away because Ti3+ oxidized to Ti4+. The colorless sapphire was colored anew into brown by ultraviolet (UV) irradiation. This coloration was discussed based on some defects in Al2O3. By UV irradiation, TiAlIV+ changed into TiAlIII× and hole (h+). The hole was trapped in VAl3−, and the resultant color center caused brown coloration. In order to prevent the valence change, co-doping with (Ti–Fe) and (Ti–Mg) was attempted. Then, the brown coloration decreased successfully.