Effect of swift heavy ion irradiation on the optical properties of sapphire

Single crystals of sapphire (Al 2 O 3 ; Fe, Ti, Cr) were irradiated with 100 MeV Ti and 100 MeV Ni swift heavy ions (SHI) at fluence 1 × 10 12 , 5×10 12 and 1×10 13 ions/cm 2 . Photoluminescence (PL) spectra of pristine and irradiated sapphires were recorded at room temperature under 2.8 eV blue excitation. A broad band consisting of two emission bands centered at 2.48 and 2.30 eV corresponding to F 2 and F 2 2+ defect centers, respectively, were observed. The concentration of these centers increases monotonically with the Ti ions fluence. While in Ni irradiated sapphires, it increases up to 5×10 12 ions/cm 2 and then showed a decreasing trend at fluence 1×10 13 ions/cm 2 . The changes in concentration of these defect centers are explained in term of creation of new defect centers (oxygen vacancies), cluster formation and quenching of these defect centers and are correlated with the nature of ions.