Optical and selected thermal properties of samarium-doped fluorochlorozirconate (FCZ) glass-ceramics: Formation and growth of BaCl 2 nanocrystals in FCZ glass-ceramics Cyril Koughia a , Go Okada a , Dancho Tonchev a , Safa Kasap a, ⁎, Andy Edgar b , Christopher R. Varoy b , Heinz von Seggern c a Department of Electrical and Computer Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A9, Canada b School of Chemical and Physical Sciences and MacDiarmid Institute, Victoria University of Wellington, New Zealand c Institute of Materials Science, Technische Universitaet, Darmstadt, D-64287, Germany abstract article info Article history: Received 30 June 2010 Received in revised form 30 September 2010 Accepted 2 November 2010 Available online xxxx Keywords: DSC; Temperature modulated DSC; Fluorochlorozirconate glass-ceramics; Thermal properties; Photoluminescence Photoluminescence (PL) and conventional and modulated temperature differential scanning calorimetry (DSC and MDSC) experiments have been carried out on a typical fluorochlorozirconate glass and glass- ceramics doped with Sm 3+ and Sm 2+ introduced by the addition of SmF 3 and a reducing agent, NaBH 4 , into the initial mixture of constituents. The nominal FCZ composition was 53% ZrF 4 , 20% NaF, 3% AlF 3 , 3% LaF 3 , 1% SmF 3 , 1% BaF 2 , 19% BaCl 2 (molar percentages). Prior to DSC and PL measurements, some of the glasses have been heat treated (annealed at an elevated temperature) under different conditions, which has resulted in glass-ceramics containing BaCl 2 nanocrystals with a hexagonal and/or orthorhombic crystal structure, depending on the heat treatment conditions. Hexagonal nanocrystals may be obtained by a simple one step annealing process while the formation of orthorhombic crystallites requires sequential multistep annealing treatments. Long duration, low temperature annealing, required for the formation of orthorhombic BaCl 2 nanocrystals, leads to the appearance of an endothermic enthalpy peak at around 250 °C on the conventional DSC thermogram. Temperature modulated DSC experiments identify a clear glass transformation in this regions; and the endothermic peak has been attributed to the structural relaxation enthalpy in the host glass which is usually obscured by the thermal effects associated with the formation of BaCl 2 nanocrystals. The observed thermodynamic effects correlate with the suppression of the broad PL band around 900 nm, which is most likely due to Sm 2+ ions near or in the “shell-region” of the glass surrounding the nanocrystals. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Fluorochlorozirconate (FCZ) glasses are based on well known fluorozirconate (FZ) glasses. The structure of FZ glasses comprises an edge or corner-sharing ZrF n polyhedral network with associated network-modifying sodium and barium ions. The FZ glasses are well known for their ability to accommodate a high concentration of rare- earth (RE) ions. FCZ glasses are produced by partially substituting fluorine ions by chlorine ions. Although FCZ glasses have poorer thermal stability than FZ glasses, their various structural transforma- tions at different temperatures open up the possibility of preparing glass-ceramics (GCs) with interesting properties, and potential applications; Eu and Sm-doped FCZ GCs show potential as phosphors for x-ray imaging. When suitably annealed, FCZ glasses show the precipitation of barium chloride (BaCl 2 ) nanocrystals in two different structural phases, depending on the annealing conditions; the two crystalline phases correspond to the orthorhombic and hexagonal structures. The FCZ GCs have a continuous glass matrix with embedded BaCl 2 crystallites. Certain RE ions such as Eu 2+ and Sm 2+ become embedded in BaCl 2 crystallites upon the formation of these crystallites during annealing at a high temperature. Further, these glass-ceramics are also highly transparent, which reduces light scattering, and hence makes these phosphors potentially interesting for practical applications, including x-ray imaging [1,2]. The most popular rare-earth ion used in FCZ glass-ceramics is Eu 2+ (e.g. [3,4]). It is known to emit light in the blue-violet region, which is an excellent match to most popular photomultipliers. As we have already mentioned, the structure of BaCl 2 nanocrystals embedded in the FCZ glass may be hexagonal or orthorhombic. The glass-ceramics with the orthorhombic BaCl 2 nanocrystals are known to possess a strong photo-storage effect whereas those with hexagonal crystallites seem to have scintillating properties [5–7]. Unlike Eu 2+ -doped FCZ glass-ceramics, there have been only very limited studies of Sm 2+ Journal of Non-Crystalline Solids xxx (2010) xxx–xxx ⁎ Corresponding author. E-mail addresses: cyril.koughia@usask.ca (C. Koughia), safa.kasap@usask.ca (S. Kasap). NOC-15184; No of Pages 6 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.11.079 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol Please cite this article as: C. Koughia, et al., Optical and selected thermal properties of samarium-doped fluorochlorozirconate (FCZ) glass- ceramics: Formation and growth of BaCl 2 nanocrystals..., J. Non-Cryst. Solids (2010), doi:10.1016/j.jnoncrysol.2010.11.079