Figure 1: (a) PL emission of samples is annealed at 1100°C for 1 h in reducing atmosphere (red solid curve), and in Ar gas (black dashed curve), and then is annealed at 510°C in reducing atmosphere (blue dotted curve). (b) PL from a sample is annealed at 1100°C in reducing atmosphere for 1 h (red solid curve) and then for 1 h (green dotted curve) and 2 h (blue dashed curve). The excitation wavelength was 250 nm.