Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol Nd/La, Nd/Lu-co-doped transparent lead fluoroborate glass-ceramics O.B. Petrova a , D.A. Velichkina a , M.P. Zykova a , A.V. Khomyakov a , M.A. Uslamina b , K.N. Nischev b , A.A. Pynenkov b , R.I. Avetisov a , I. Ch. Avetissov a, ⁎ a Department of Chemistry and Technology of Crystals Mendeleev University of Chemical Technology of Russia, Miusskaya sq. 9, Moscow, 125047, Russia b Institute of Physics and Chemistry N.P. Ogarev Mordovia State University, Bolshevistskaya Str., 68, Saransk, Republic of Mordovia, 430005, Russia ARTICLE INFO Keywords: Oxyfluoride glass Glass-ceramic Lead fluoride Fluorescence Neodymium ABSTRACT The glasses in PbF 2 –B 2 O 3 -REF 3 (RE = Nd, Nd+La, Nd+Lu) system have been synthesized. The initial glasses were doped with several RE's (0.2–3.0 at%), one of which had no luminescent f–f transitions (La, Lu) and performed only the function of the stabilizer of the cubic phase PbF 2 , and the other (Nd) played the role of a luminescence center. Glass-ceramics have been obtained by the controlled crystallization of glasses with for- mation of Pb 1-x La/Nd x F 2+x or Pb 1-x Lu/Nd x F 2+x solid solutions. The luminescence spectra of co-activated glass- ceramics as well as crystalline samples demonstrated a splitting of the «0–0» line for the 4 F 3/2 → 4 I 9/2 transition. It has been shown that it is possible to stabilize a cubic phase based on PbF 2 by several RE co-doping and to obtain glass-ceramics with a crystalline phase in which the concentration quenching was reduced compared to glass- ceramics doped with a single activator. 1. Introduction Glass ceramic materials (GC's) despite a long history of production, remain extremely promising for various fields of technology and are actively explored to the date [1]. One of the main task within the frame of luminescent and laser materials development is the production of a highly transparent GC with luminescent properties close to the corre- sponding crystalline phase. To achieve high transparency of the GC we need the concurrent existence of three following parameters: crystallite sizes of 20–100 nm, the minimum difference in refractive indices be- tween the residual glass phase and crystallites at a level of 0.01, and the structure of the crystalline phase, which excludes birefringence, i.e. cubic structures [2]. Oxyfluoride GC's combine the best properties of crystalline fluorides and oxide glasses, which make them promising for doping with rare- earth (RE) ions and creating novel laser materials [3–5]. The high lu- minescence efficiency of oxyfluoride GC's is associated with the fact that the RE activator is mainly located in a crystalline fluoride en- vironment with a low phonon energy of the crystal lattice, which suppresses nonradiative relaxation [6]. The phonon energy decreases with an increasing mass of the cation; therefore, GC's with the crys- talline phase based on lead fluoride are being intensively investigated. Thus, the maximum phonon energy in the β-PbF 2 crystal is 250 cm -1 [7], while in other cubic crystals with the same structure it is much higher, namely, 466 cm -1 in CaF 2 , 366 cm -1 in SrF 2 , and 319 cm -1 in BaF 2 [8], and the phonon energy in oxide glass is about 1500 cm -1 [7]. So, the lead oxyfluoride glasses, whose composition may vary within a wide range, are good precursors for GC's. Lead oxyfluoride GC's have been made in silicate [6–7,9–11], borate [12–17], germanate [18], phosphide [19], and telluride [20,21] systems. In the most cases in silicate [7,9–10] and borate [12–17] glass systems one has obtained a high-temperature cubic β-PbF 2 phase (Fm3m fluorite type) doped with RE ions. However, sometimes the low- temperature rhombic α-PbF 2 phase (Pnma cotunnite type) precipitated and RE did not intercalate into these precipitates [14]. α-PbF 2 phase is a birefringent phase which causes parasitic scattering and transparency losses in GC. It is known that stabilization of the cubic β–PbF 2 phase is possible by the formation of solid solutions based on bivalent metal fluorides with an isostructural crystal lattice (CdF 2 [6,11], BaF 2 [12]). But the usage of CdF 2 results to the decrease of isomorphic capacity of RE and reduced the chemical resistance [11]. At the same time. there is a possibility of heterovalent stabilization of high-temperature cubic β- PbF 2 phase by trivalent rare-earth ions [13], which are also introduced as activators in laser materials. https://doi.org/10.1016/j.jnoncrysol.2019.119858 Received 25 October 2019; Received in revised form 25 November 2019; Accepted 8 December 2019 ⁎ Corresponding author. E-mail address: aich@muctr.ru (I. Ch. Avetissov). Journal of Non-Crystalline Solids 531 (2020) 119858 0022-3093/ © 2019 Elsevier B.V. All rights reserved. T