Photoluminescence studies of 100Â MeV Ni8+ ion irradiated Al2O3 single crystals

We present the results of photoluminescence (PL) measurements on 100 MeV Ni8+ ion irradiated Al2O3 single crystals in the fluence range 1 × 1011 to 5 × 1012 ions/cm2. A sharp PL peaks at ∼693, 695, 707 and 730 nm are recorded with an excitation of 442 nm He-Cd laser beam. The sharp emission peaks at 693 and 695 nm are attributed to R2 and R1 lines of Cr3+ ions, and they are related to the transition from 2Eg → 4A2g. The weaker sharp peaks called N lines appear at ∼707 nm and its origin is ascribed due to closely coupled pairs of Cr3+ ions. The longer wavelength part of the PL spectra at ∼730 nm may be due to increase of groups of more than two Cr3+ ions. It is observed that the broad emission band (450-650 nm) consists of four bands centered at 470, 518, 547 and 618 nm, respectively. The 470, 518 and 547 nm bands are corresponding to F2+, F2 and F22+ defect center, respectively. It is observed that the PL intensity of F2, F22+, R and N lines increases with Ni8+ ion fluence. This can be attributed to increase in concentration of color centers responsible for luminescence through radiative recombination.