Conditions for the formation of Ti3+ by ion implantation of a-axis α-Al2O3

Photoluminescence (PL) studies have shown that high energy ion implantation of Ti and O into a-axis sapphire, and subsequent annealing, lead to the formation of optically active Ti3+ in the sapphire matrix. The optimum implantation and annealing conditions for this purpose were investigated and compared to previous work in c-axis sapphire. The current study showed that for anneals at 1400 °C, in a reducing environment, the ratio of O to Ti did not affect the amount of Ti3+ formed in the matrix. At this temperature, the only implantation condition to affect Ti3+ formation was the Ti dose. Below 1400 °C, the optimum O to Ti ratio was 3/2 and there is a saturation dose of Ti, about 0.1 at.%, above which roll-off in the gain is observed. Rutherford backscattering analysis revealed that anneals at 1400 °C and above result in significant redistribution of the Ti in the near-surface region. The optical anisotropy of sapphire was also investigated by Raman spectroscopy and photoluminescence. When the incoming radiation is polarised parallel to the c-axis, the Ti3+ luminescence is 5–6 times higher than when the radiation is polarised perpendicular to the c-axis.