New Journal of Glass and Ceramics, 2012, 2, 65-74 http://dx.doi.org/10.4236/njgc.2012.22010 Published Online April 2012 (http://www.SciRP.org/journal/njgc) 65 Thermal and Structural Characterization of Transparent Rare-Earth Doped Lead Fluoride Glass-Ceramics Chaouki Bensalem 1,2 , Michel Mortier 1* , Daniel Vivien 1 , Patrick Gredin 1 , Gilles Patriarche 3 , Madjid Diaf 2 1 Laboratoire de Chimie de la Matière Condensée de Paris, UPMC, Chimie ParisTech, Paris, France; 2 Département de Physique, Univer- sité d’Annaba, Annaba, Algérie; 3 Laboratoire de Photonique et Nanostructures, Marcoussis, France. Email: * michel-mortier@chimie-paristech.fr Received December 1 st , 2011; revised January 9 th , 2012; accepted January 22 nd , 2012 ABSTRACT The devitrification of glasses with composition 50GeO 2 -40PbO-10PbF 2 -xREF 3 , RE = Gd, Eu, 0 < x ≤ 2, leads to glass ceramics made of RE 3+ : β-PbF 2 nanocrystals embedded in a glassy oxide matrix. This transformation is investigated using thermal analysis, X-ray diffraction and electron microscopy. A comparison with RE 3+ : β-PbF 2 ceramics prepared by standard ceramic techniques is performed. The Rare Earth cations show a strong nucleating effect for the precipita- tion of the RE 3+ : β-PbF 2 nanocrystals. The evolution of the unit cell parameters of the REF 3 : β-PbF 2 solid solution re- sults from a combined effect of Pb 2+ -RE 3+ substitution and interstitial F – introduction. In the glass ceramics, RE 3+ : β-PbF 2 nanocrystals are constrained by the glassy matrix when they form with a pressure equivalent to 1.6 GPa. The constrained nanocrystals can return to a relaxed state by chemical dissolution of the embedding glassy matrix, fol- lowed by thermal treatments. Keywords: Glass-Ceramic; Rare-Earth; Thermal Analysis; Devitrification; Nanocrystallite; X-Ray Diffraction 1. Introduction Transparent oxyfluoride nano-glass-ceramics made pho- toluminescent by doping with Rare-Earth (RE) ions have been shown recently to be promising materials for new optical devices such as bulk laser media and amplifying laser fibers for optical communications [1-7]. These ma- terials are easier to prepare than single crystals and can be made in a wide variety of shape and size. They are obtained by casting of a glass, using standard glass tech- nology, followed by an appropriate heat treatment to ge- nerate the precipitation of fluoride nanocrystallites in the remaining oxide glass. Transparent glass-ceramics have interesting optical properties, since they exhibit narrower emission linewidths and higher emission crosssection than their parent glasses [4]. Therefore, they combine the processing ability of the glasses with the outstanding op- tical properties of the crystals. For about ten years, we are engaged in the investiga- tion of lanthanide-activated transparent oxyfluoride glass- ceramics prepared by annealing of glasses with typical composition 50GeO 2 -40PbO-10PbF 2 -xREF 3 , in which the doping ions, which act as nucleating agents, are confined in β-PbF 2 nanocrystals [5,8-10]. Recently, we have reported optical investigation of EuF 3 doped lead fluorogermanate glasses [11], revealing that Eu 3+ ions are not statistically distributed in the glass, but incorporated in fluorine rich islands separated by chains of GeO 4 anions linked together. We have also compared the transparent glass-ceramic containing Eu 3+ : β-PbF 2 nanocrystallites obtained by devitrification of the above mentioned glass with the europium activated β-PbF 2 ceramics [12]. It has been shown that their optical properties are almost identical and that, in these materials, europium ions are not isolated but engaged in dimers and higher nuclearity clusters. Furthermore, in co-doped Gd 3+ : Eu 3+ : β-PbF 2 ceramics, efficient energy transfer from Gd 3+ to Eu 3+ occurs [12]. This property might be used for in- stance for making photon-cutting phosphors for solar energy conversion and mercury-free fluorescent lamps [13,14]. The present paper is devoted to the investigation of the transition between the glass and glass-ceramic in RE doped lead fluorogermanate glass, RE = Eu or Gd. It reports also the study of the lead fluoride nanoparticles of the glass-ceramic using both electron microscopy and X- ray diffraction. It will be shown that these nanocrystals are constrained, with a unit cell parameter decrease that can reach about 1% with respect to this of the ceramic of * Corresponding author. Copyright © 2012 SciRes. NJGC