Photoluminescence study of swift heavy ion (SHI) induced defect centers in sapphire K.S. Jheeta a , D.C. Jain a, * , Ravi Kumar b , Fouran Singh b , K.B. Garg a a Department of Physics, University of Rajasthan, Jaipur 302 004, India b Nuclear Science Center, Aruna Asaf Ali Marg, New Delhi 110 067, India Received 15 August 2005; accepted 24 January 2006 Abstract Single crystals of sapphire (Al 2 O 3 : Fe, Ti, Cr) were irradiated at room temperature with different fluence of 100 MeV Ni ions. Photoluminescence (PL) spectra of pristine and irradiated sapphires were recorded at room temperature under 2.8 eV blue excitation. A broad emission band consists of two bands centered at 516 nm corresponding to F 2 defect center and 546 nm corresponding to F 2þ 2 defect center was observed. The intensity of these defect centers was found to vary with the fluence. F 2þ 2 defect center develops at low fluence reaching maximum at 5 · 10 16 ions/m 2 and finally decreasing at higher fluence. The behavior is interpreted in terms of creation of defect centers, their clustering and annihilation. Ó 2006 Elsevier B.V. All rights reserved. PACS: 61.72.y; 61.82.Ms; 78.55.m 1. Introduction Alumina (sapphire) possesses a wide band gap and is a radiation hard insulator. It can be applied in the field of optics, fusion reactors as an insulator and for optical window [1,2]. The optical properties of this material can be modified by point and extended defects, created due to different type of particle irradiation [3–5]. The defect centers induced by ion irradiation in sapphire are mainly F center, F + center, F 2 centers, F þ 2 centers and F 2þ 2 centers. These centers are associated with luminescence bands centered at 415, 330, 518, 385 and 550 nm, respectively [4]. Understanding of radiation induced processes (light emission and defect production) is the important issue for prospective use of optical and insulating materials based on Al 2 O 3 , for exam- ple, in the diagnostic systems of fusion reactors [6]. Although, a number of such studies using low energy heavy ions irradiation in sapphire [7–9] have been made, there is a lack of sufficient and system- atic work to correlate the defects center formation due to swift heavy ions. High-energy ions upon entering a medium lose their energy initially through the process of electronic excitation and ion- ization known and at the end of its range by nuclear loss [10]. It is established that the concentration of primary defect centers (F and F + centers) increases as a result of irradiation by energetic ions [11,12]. It 0022-3115/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2006.01.017 * Corresponding author. Tel.: +91 141 2390458; fax: +91 141 2701038. E-mail addresses: kuldeep_jheeta@yahoo.com (K.S. Jheeta), dhaneshcjain@yahoo.com (D.C. Jain). Journal of Nuclear Materials 353 (2006) 190–192 www.elsevier.com/locate/jnucmat