Optical property changes in sapphire induced by triple-energy Cu and O implantation

Triple-energy Cu and O ions were implanted into sapphire, changing the ratios of Cu and O doses and the implantation sequence as follows: Cu only (1:0); Cu+1/2O (1:0.5); Cu+O (1:1); 1/2O+Cu (0.5:1); and O+Cu (1:1) at room temperature (300 K). Optical property changes induced by the ion implantations and successive heat treatments were studied. Specific optical absorption is clearly observed at approximately 590 nm, which is attributed to Cu nano-particles, for Cu-implanted sapphire after annealing at 1070 and 1270 K. The intensity is drastically changed between 1070 and 1270 K. A broad absorption centered at approximately 300 nm is also observed for samples annealed at 770 and 1070 K. For Cu and O co-implantation, an increase in O dose leads to lower absorption on the whole. The absorption at approximately 590 nm is observed after annealing at 1070 or 1270 K for Cu+1/2O and Cu+O, but not for 1/2O+Cu and O+Cu implantation. In general, optical absorption of sapphire increases after annealing, especially in the short-wavelength region, and this can be attributed to copper oxide formation. The formation of Cu, Cu2O and CuO nanoparticles was confirmed by XRD measurements. CuO and Cu2O are easily formed at a lower annealing temperature, whereas Cu nanoparticle formation requires a higher annealing temperature. The sequence of ion implantation for Cu and O affects the optical absorption and nanoparticle formation.