Figure 3

PL excitation/emission spectra of the specimens. (a) PL excitation/emission spectra of 0.10% Cu-doped specimens. The monitored and excitation wavelength were 440Â nm and 260Â nm, respectively. PL spectrum of (b) Cu(0.10%)-Ar and (c) Cu(0.10%)-air specimens fitted by double gaussians. (d) Ratio of the spectral area with a peak at 424Â nm to the spectral area with a peak at 467Â nm.