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

We present the results of photoluminescence (PL) measurements on 100 MeV Ni(8+) ion irradiated Al(2)O(3) single crystals in the fluence range 1x10(11) to 5x10(12) ions/cm(2). A sharp PL peaks at approximately 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 R(2) and R(1) lines of Cr(3+) ions, and they are related to the transition from (2)E(g)-->(4)A(2g). The weaker sharp peaks called N lines appear at approximately 707 nm and its origin is ascribed due to closely coupled pairs of Cr(3+) ions. The longer wavelength part of the PL spectra at approximately 730 nm may be due to increase of groups of more than two Cr(3+) 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 F(2)(+), F(2) and F(2)(2+) defect center, respectively. It is observed that the PL intensity of F(2), F(2)(2+), R and N lines increases with Ni(8+) ion fluence. This can be attributed to increase in concentration of color centers responsible for luminescence through radiative recombination.