Journal of Luminescence 109 (2004) 19–24 Luminescence channels of manganese-doped spinel Ayana Tomita a , Tokushi Sato a , Kensuke Tanaka a , Yutaka Kawabe a,b , Masanobu Shirai b,c , Kouichirou Tanaka b,c , Eiichi Hanamura a,b, * a Chitose Institute of Science and Technology, 758-65 Bibi, Chitose 066-8655, Japan b Japan Science and Technology Corporation, 758-65 Bibi, Chitose 066-8655, Japan c Department of Physics, Kyoto University, Kyoto 606-8224, Japan Received 24 September 2003; received in revised form 1 December 2003; accepted 16 December 2003 Abstract Two independent luminescence channels are observed from manganese-doped spinel Mn:MgAl 2 O 4 . The luminescence around 520 nm is assigned to transition from the lowest electronic excited state 4 T 1 to the ground state 6 A 1 of Mn 2+ (3d) 5 ion by analyzing the excitation spectrum and electron spin resonance measurement. The emission at 650 nm is triggered by the band edge excitation and is assigned similarly to the charge-transfer process associated with the manganese ion. r 2004 Elsevier B.V. All rights reserved. PACS: 76.30.Fc; 76.30.Mi; 78.47.+p; 78.55.m Keywords: d–d Transition; Charge-transfer excitation; Manganese-doped spinel; Color center; Mn:MgAl 2 O 4 1. Introduction Sapphire crystals doped with transition metal such as Ti:Al 2 O 3 and Cr:Al 2 O 3 are famous laser materials, while optical properties of Cr 2 O 3 with the same corundum structure as Al 2 O 3 have been studied experimentally and theoretically. The optical responses of both these doped and pure crystals have been successfully analyzed by the localized model of electronic excitation between 3d-orbitals of the transition metal [1, 2]. Hereafter we call them d–d transitions. On the other hand, optical properties of perovskite structure such as YFeO 3 [3] and La 2 CuO 4 [4] are quite different from those of the corundum. In the perovskite, 3d- orbitals of the transition metal extend toward the O-2p s orbital so that both of them are well hybridized. As a result, the oscillator strength of this charge transfer excitation which is distributed in visible region becomes larger than that of d–d transition by two or three orders of magnitude. It is also noted that this excitation can propagate in the perovskite but the d–d transition is well localized at the transition metal in the corundum. Optical properties of spinel crystals MgAl 2 O 4 have been studied, e.g., on persistent phosphorescence [5], ARTICLE IN PRESS *Corresponding author. Chitose Institute of Science and Technology, Bibi, Chitose 066-8655, Japan. Tel./fax: +81-123- 27-6171. E-mail address: hanamura@photon.chitose.ac.jp (E. Hanamura). 0022-2313/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2003.12.049