Effect of the PVA (polyvinyl alcohol) concentration on the optical properties of Eu-doped YAG phosphors Daniela A. Hora a , Adriano B. Andrade a , Nilson S. Ferreira b , Ver ^ onica C. Teixeira c, * , Marcos V. dos S. Rezende d a Departamento de Física, Universidade Federal de Sergipe, 49100-000, S~ ao Crist ov~ ao, SE, Brazil b Departamento de Física, Universidade Federal do Amap a, 68902-280, Macap a, AP, Brazil c Laborat orio Nacional de Luz Síncrotron, Centro Nacional de Pesquisa em Energia e Materiais, P.O. Box 6192,13084-971, Campinas, SP, Brazil d Grupo de Nanomateriais Funcionais (GNF), Departamento de Física, Universidade Federal de Sergipe, 49500-000, Itabaiana, SE, Brazil article info Article history: Received 6 July 2016 Received in revised form 22 August 2016 Accepted 6 September 2016 Keywords: PVA based sol-gel XEOL Luminescence Phosphors Eu-doped YAG abstract The influence of the polyvinyl alcohol (PVA) concentration on the synthesis and structural, morpho- logical and optical properties of Y 3 Al 5 O 13 : Eu (Eu-doped YAG) was systematically investigated in this work. The final concentration of PVA in the preparation step influenced the crystallite size and also the degree of particle agglomeration in Eu-doped YAG phosphors. X-ray excited optical luminescence (XEOL) emission spectra results indicated typical Eu 3þ emission lines and an abnormally intense 5 D 0 / 7 F 4 . The intensity parameters U 2 and U 4 were calculated and indicated the PVA concentration affects the ratio U 2 :U 4 . X-ray absorption spectroscopy (XAS) results showed Eu valence did not change and the symmetry around the Eu 3þ is influenced by the PVA concentration. XEOL-XAS showed the luminescence increases as a function of energy. © 2016 Elsevier B.V. All rights reserved. 1. Introduction Yttrium aluminate garnet (Y 3 Al 5 O 12 -YAG) has been largely investigated for application as a host to prepare photonic sources. It has a high thermal stability and its crystalline structure present two trivalent cationic sites able to accommodate doping ions such as rare earths, which are, for example, responsible for luminescence properties [1e5]. Doped YAG has been applied in X-ray tubes, low voltage field emission displays (FEDs), vacuum fluorescent displays [6e10], X-ray digital imaging detectors, X-ray micro-radiography and it is also suitable for X-ray imaging with high spatial resolu- tion [11e 13]. Particularly, Eu-doped YAG has been cited as a red emitter phosphor, which has potential applications in photonics, mainly in optical display and lighting, such as light emitting diodes (LEDs), plasma panel displays (PDPs), FEDs [3,14e16], fluorescence thermometry [17], etc. YAG is a versatile host, which can be obtained as crystal or ceramic powders [18e20]. In both cases, it is possible to manipulate its properties by the insertion of impurities on the host structure. However, the ceramics can be produced by simpler methods than the crystals and their characteristics may be strongly affected by the way they are grown. For example, for nanosized grains, when compared to the bulk ones, they can present completely new properties [21]. In this case, the surface/volume ratio is high and the surface effects, which come from the surface dangling bonds, or quantum confinement effects may determine the material prop- erties [21,22]. Several works report methodologies to synthesize luminescent materials in ceramic powder form, for example, solid state reaction [23], co-precipitation [24], solvothermal [25], combustion [26], glycothermal treatment [27], spray pyrolysis [28], conventional sol- gel [29], sol-gel assisted by organic molecules, polymers [30e35], etc. The conventional solegel route uses alkoxides for the hydro- lysis and condensation of the precursors. However, this method has been recently modified by the use of other organic agents con- taining alcohol and/or carboxylic acid groups, such as ethylene glycol, coconut water [30,31], natural organic matter [32], PVA (polyvinyl alcohol) [33e36], etc. The sol-gel assisted by PVA, [C 2 H 4 O] n , for example, has been used in order to produce magnetic, biocompatible, and luminescent materials [33e36] and this method was employed to produce the Eu-doped YAG phosphors * Corresponding author. E-mail address: veronica.teixeira@lnls.br (V.C. Teixeira). Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat http://dx.doi.org/10.1016/j.optmat.2016.09.011 0925-3467/© 2016 Elsevier B.V. All rights reserved. Optical Materials 60 (2016) 495e500