Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat X-ray absorption spectroscopy and tunable color emission study of the Mn- co-doped BaAl 2 O 4 : Ce phosphor under synchrotron radiation Simone S. Melo ∗ , Adriano B. Andrade, Giordano F.C. Bispo, Jessica C. Carvalho, Zélia S. Macedo, Mário E.G. Valerio Laboratory of Preparation and Characterization of Materials, Physics Department, Federal University of Sergipe, 49100-000, São Cristovão, SE, Brazil ARTICLE INFO Keywords: X-ray absorption spectroscopy Mn and Ce co-coped BaAl 2 O 4 Scintillator Tuning luminescence ABSTRACT This work reports the scintillator properties of barium aluminate undoped, Ce-doped and Ce and Mn co-doped phosphors. The samples were produced using the PVA-modified sol-gel route. The oxidation states of the dopants were investigated by X-ray absorption spectroscopy in the range of excitation energies that includes Ba L III -edge, Ce L III -edge and Mn K-edge. A multiple valence mixture was observed for both cerium and manganese. The luminescent centers were investigated using X-ray excited optical luminescence (XEOL) near the absorption L III - edge of barium. The host emissions, as well as characteristic emissions from the dopants, were observed. The color of the scintillator emission was tuned by varying the co-dopant concentration. 1. Introduction The alkaline earth aluminate phosphors based on XAl 2 O 4 (X = Ba, Ca, and Sr) belong to the class of luminescent materials that exhibit persistent luminescence emission, high quantum efficiency in the visible range and radiation hardness [1–3]. The persistency of the lu- minescence displayed for these materials have been widely studied by many authors. The mostly reported materials are SrAl 2 O 4 :Eu 2+ , Dy 3+ and CaAl 2 O 4 :Eu 2+ , Nd 3+ , that can display a persistent emission for more than 24 h [4,5]. Some studies have shown that persistent emission displayed by these aluminate phosphors is very dependent on the synthesis conditions, doping concentration, and also sintering proce- dures [6–8]. Recent studies on Eu 3+ -doped BaAl 2 O 4 , Eu 3+ -doped CaAl 2 O 4 , and Eu 3+ -doped SrAl 2 O 4 have reported scintillation emission as a broad-band due Eu 2+ spanning from green to blue region when the sample was kept under X-ray exposure. In these cases, the emission was related to the Eu 3+ to Eu 2+ conversion due the ionizing radiation effect [9–11]. Besides that, these works also shown that the Eu 2+ is not stable after X-ray exposure since the photoluminescence, under excitation with UV before and after X-ray irradiation, revealed the presence of only the Eu 3+ typical 4f-4f transitions [11]. Efficient green and blue emission without persistent luminescence in BaAl 2 O 4 phosphors was reported for Mn 2+ and Ce 3+ doping, re- spectively [12]. Manganese and cerium co-doped BaAl 2 O 4 is a pro- mising phosphor for color tunable emission due the fact that cerium can efficiently sensitize the manganese luminescence by energy transferring to manganese ions [13]. Cerium is the most common dopant ion used for extrinsic scintillator materials due to their short lifetime (20–50 ns) [14,15]. Manganese luminescence has been studied in several inorganic compounds as silicates, aluminates, and sulfides for visible light emis- sion that can be in the green and red region depending on the host matrix due to the strong influence of the crystal field in the manganese 3d-3d transitions [12,16]. Mn is also an interesting dopant because it can exhibit multiple valence charge states that may produce different emitting colours, and this feature can be used to tune the radiation conversion light emission to the light detecting system used in different radiation detection devices. In the present work, Ba (1-x-y) Ce (x) Mn (y) Al 2 O 4 phosphors were stu- died, where x, y can be one of the following dopant concentration combinations 0, 0; 0.02, 0; 0.02, 0.01; 0.02, 0.005; 0, 0.02. The samples were synthesized via a modified sol-gel route using polyvinyl alcohol (PVA) as metal complexing agent [17]. Scintillator emission was in- vestigated via radioluminescence measurements. X-ray diffraction measurements were performed in order to check the crystalline phase formation. X-ray absorption spectroscopy (XAS) were used to identify the oxidation state of the doping ions and X-ray excited optical lumi- nescence (XEOL), using monochromatic X-rays from synchrotron ra- diation tuned at the Ba L III -edge, Ce L III -edge, and at the Mn K-edge, was recorded as a function of the incident X-ray photon energy. https://doi.org/10.1016/j.optmat.2019.03.052 Received 31 December 2018; Received in revised form 14 March 2019; Accepted 28 March 2019 ∗ Corresponding author. E-mail address: fisicasimone@gmail.com (S.S. Melo). Optical Materials 91 (2019) 401–407 0925-3467/ © 2019 Elsevier B.V. All rights reserved. T