Effect of Al/Sr ratio on the luminescence properties of SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphors Selvin Yes ¸ilay Kaya a, * , Erkul Karacaoglu b , Bekir Karasu b a Anadolu University, Faculty of Fine Arts, Department of Glass, Eskisehir, Turkey b Anadolu University, Faculty of Engineering and Architecture, Department of Materials Science and Engineering, Eskisehir, Turkey Received 14 December 2011; accepted 4 January 2012 Available online 21 January 2012 Abstract Recent studies have brought out many phosphors like Eu 2+ , Dy 3+ -doped alkaline earth aluminates. The trivalent Dy 3+ ions as co-dopants greatly enhance the duration and intensity of persistent luminescence. These phosphors show excellent properties, such as high quantum efficiency, long persistence of phosphorescence, good stability and suitable color emission. In this work the effect of Al/Sr ratio on the afterglow and phosphorescence decay properties of Eu 2+ and Dy 3+ co-activated strontium aluminates synthesized by a solid-state process has been investigated. The luminescence properties of samples were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis. A variety of strontium aluminates, such as SrAl 2 O 4 , Sr 4 Al 2 O 7 , Sr 3 Al 2 O 6 , Sr 3 Al 2 (Eu, Dy, Y)O 7.5 , Al 5 (Eu, Dy, Y)O 12 , Sr 4 Al 14 O 25 , SrAl 12 O 19 and (Eu, Dy, Y)AlO 3 have been identified in the samples prepared from starting precursors with Al/Sr mole ratios ranging from 0.44 to 5. The afterglow decay rate was found to be the fastest for sample with Al/Sr ratio of 4.18, in which SrAl 4 O 7 phase was dominant. The afterglow decay rate for phosphor with Al/Sr ratio of 2, in which SrAl 2 O 4 phase was dominant, was detected to be slow. Moreover, the emission spectra of the samples shift to yellow-green long wavelength from bluish-green-ultraviolet short wave with the increase of Al/Sr ratios resulting from the change in the composition. # 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Long persistence phosphorescence; Strontium aluminates; Al/Sr ratio; Crystal 1. Introduction In general, a phosphor is a solid that converts certain types of energy into electromagnetic radiation over and above the thermal radiation. The term luminescence, which includes both fluorescence and phosphorescence, is defined as a phenomenon, in which the electronic states of substance is excited by some kind of external energy and the excitation energy is given off as light of various wavelengths [1]. In 1990s, Matsuzawa reported a new type of long persistent phosphor, SrAl 2 O 4 :Eu 2+ /Dy 3+ , with a strong emission centered at 520 nm (green). The persistent time of this SrAl 2 O 4 :Eu 2+ /Dy 3+ phosphor was found to be longer than 16 h [2–4]. Double oxides containing strontium and aluminum have become of interest in material science since they exhibit excellent properties, such as high quantum efficiency, long persistence of phosphorescence, safety and good stability when compared with classical sulfide phosphorescent phosphors. Based on these properties, some strontium aluminates have found themselves many application fields [5–9]. The Al/Sr ratio in the strontium aluminates phosphors can affect the long duration phosphorescence [10]. In SrA- l 2 O 4 :Eu 2+ , Dy 3+ , the long duration phosphorescence was also reported to be affected by chemical composition [11,12]. However, the compositional variation of SrAl 2 O 4 :Eu 2+ , Dy 3+ in terms of phosphorescence is not so drastic. So, its effects on the long duration phosphorescence have, therefore, not been fully understood. In order to clarify this effect on the long duration phosphorescence, one must conduct researches on the crystals with wider variation in composition. Sakai et al. reported such effects in BaAl 2 O 4 :Eu 2+ , Dy 3+ . They indicated that the Al/Ba ratio has great influence on the long afterglow properties of the phosphors since Al-rich compounds have much better phosphorescence properties than Ba-rich compounds [13,14]. www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 38 (2012) 3701–3706 * Corresponding author. Tel.: +90 222 3350580x4237; fax: +90 222 3351290. E-mail addresses: selvin.yesilay@gmail.com, syesilay@anadolu.edu.tr (S. Yes ¸ilay Kaya). 0272-8842/$36.00 # 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2012.01.013