Analysis of the distribution of Tm 3+ ions in LaF 3 containing transparent glass-ceramics through X-ray absorption spectroscopy A. de Pablos-Martín a,c, ⁎, M.A. García a , A. Muñoz-Noval b , G.R. Castro b , M.J. Pascual a , A. Durán a a Instituto de Cerámica y Vidrio (CSIC), C/Kelsen 5, Campus de Cantoblanco, 28049 Madrid, Spain b Spanish CRG Beamline at the ESRF, Instituto de Ciencia de Materiales de Madrid SpLine, F-38043 Grenoble, Cedex 09, France c Fraunhofer Institute for Mechanics of Materials IWM, Walter-Hülse-Str. 1, D-06120 Halle, Germany abstract article info Article history: Received 30 November 2012 Received in revised form 18 June 2013 Available online 21 September 2013 Keywords: X-ray absorption spectroscopy; Oxyfluoride glass-ceramics; Fluoride crystals; Rare earths Incorporation of rare-earth (RE) ions in the fluoride crystals of oxyfluoride glass-ceramics greatly improves the optical properties of these materials, such as the up-conversion emission. In this work, we present a study of this incorporation using X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. Both techniques allow quantifying the distribution of these ions in the glass matrix and the fluoride crystals. We found that 27% of Tm 3+ ions are incorporated in LaF 3 nano-crystals. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The preparation of rare-earth (RE) ions-doped oxyfluoride transpar- ent glass-ceramics has been successfully used to obtain crystalline phases with very low phonon energies, like LaF 3 [1], NaLaF 4 [2] and NaYF 4 [3], by heat treatments at temperatures slightly above the transi- tion temperature (T g ) of the precursor glasses. Alumosilicate oxyfluoride glasses combine the superior optical performance of low phonon energy phases, as fluorides, with the high mechanical, chemical and thermal stability of oxide silicates [4]. It is well known that the partial distribution of the doping RE ions in the fluoride crystalline phase of the glass-ceramic enhances the radiative optical emission processes currently focused on up- and down- conversion emissions [5]. For this reason, a key point to confirm the suitability of these glass- ceramics for optical applications is to identify and quantify the inclusion of rare earth ions in the fluoride precipitated phases. From previous studies about NaLaF 4 and LaF 3 crystallisation in oxyfluoride glass-ceramics [1,2], the crystallisation mechanism of fluo- ride species was deduced to take place as follows. Initially La-enriched droplets are present in the parent glass. Upon heating, these droplets crystallise inducing a variation of the chemical composition in the inter- face between the formed crystals and the residual glassy matrix, which becomes enriched in SiO 2. This silica enriched shell acts as a diffusion barrier leading to a strong reduction of the crystal-growth rate. Thus, an effective process of nano-crystallisation is obtained. For initial glass composition of 70 SiO 2 ⋅ 7 Al 2 O 3 ⋅ 8 Na 2 O ⋅ 8K 2 O ⋅ 7 LaF 3 mol. % doped with Tm 2 O 3 , we found that NaLaF 4 nano-crystals with sizes below 30 nm precipitate during the heat treatment slightly above T g [6]. X-ray diffraction (XRD) patterns showed that the NaLaF 4 cell parameters a and c in the glass-ceramics decrease with increasing Tm 2 O 3 content from 0.1 to 0.7 mol. %, indicating a major substitution of Tm 3+ for La 3+ in the NaLaF 4 lattice with increasing Tm 2 O 3 concentra- tion. Upon excitation at 488 nm, the photoluminescence emission spec- tra of these glass-ceramics exhibit additional and narrower bands compared with those of the base glass, indicating the partial incorpora- tion of Tm 3+ into the surrounding crystalline NaLaF 4 . Moreover, under excitation at 790 nm, the up-conversion emission spectra of the glass- ceramic exhibits a much higher blue emission intensity at 450 nm with respect to that of the parent glass [7], likely due to the partial incorpora- tion of Tm 3+ ions in the NaLaF 4 nanocrystals. Further evidence of a partial incorporation of the rare earth ions into fluoride nano-crystals in oxyfluoride glass-ceramics was obtained by photoluminescence spectra [8]. In this work, a glass of composition 55 SiO 2 ⋅ 20 Al 2 O 3 ⋅ 15 Na 2 O ⋅ 10 LaF 3 mol. % doped with 1 mol. % Tm 2 O 3 was investigated. LaF 3 nano-crystals of 20 nm precipitated during the heat treatment of the parent glass. Similar to NaLaF 4 glass-ceramics mentioned above, the differences between glass and glass-ceramic photoluminescence spectra pointed out that Tm 3+ ions are partially incorporated in the LaF 3 nano-crystals. As in the previous case, Tm 3+ up-conversion spectra under 790 nm excitation present a higher blue emission at 450 nm intensity in the glass-ceramic compared with that in the glass, related with the partial distribution of Tm 3+ ions in the Journal of Non-Crystalline Solids 384 (2014) 83–87 ⁎ Corresponding author at: Instituto de Cerámica y Vidrio (CSIC), C/Kelsen 5, Campus de Cantoblanco, 28049 Madrid, Spain. Tel.: +34 917355840. E-mail address: araceli.pablos@icv.csic.es (A. de Pablos-Martín). 0022-3093/$ – see front matter. © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnoncrysol.2013.07.021 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol