Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol Copper nanoparticles enhanced luminescence of Eu 3+ doped lead tellurite glass ceramics Razvan Stefan a,b , Liviu Calin Bolundut c , Lidia Pop c , Gheorghe Borodi d , Eugen Culea c, ⁎ , Petru Pascuta c, ⁎ a University of Agricultural Science and Veterinary Medicine, 3-5 Calea Manastur, 400372 Cluj-Napoca, Romania b Life Sciences Institute, 3-5 Calea Manastur, 400372 Cluj-Napoca, Romania c Technical University of Cluj-Napoca, 103-105 Muncii Avenue, 400641 Cluj-Napoca, Romania d National Institute for Research and Development of Isotopic and Molecular Technologies, 65-103 Donath, 400293 Cluj-Napoca, Romania ARTICLE INFO Keywords: Lead-tellurite glass ceramics XRD UV-VIS Photoluminescence EPR Magnetic susceptibility ABSTRACT Structural, optical and magnetic properties of some lead tellurite glass ceramics doped with europium(III) ions and co-doped with fixed amounts of metallic copper nanoparticles (CuNPs) or copper(II) ions (via CuO) were investigated. Samples in the (Eu 2 O 3 ) x ·(TeO 2 ) 80 ·(PbO) (19.7-x) ·(CuNPs) 0.3 and (Eu 2 O 3 ) x ·(TeO 2 ) 80 ·(PbO) (19.7- x) ·(CuO) 0.3 systems with 0 ≤ x ≤ 10 mol% were obtained and investigated for the first time. Several techniques such as X-ray diffraction, UV-VIS, EPR and luminescence spectroscopies and density and magnetic susceptibility measurements were used in order to characterize the samples. XRD data show that the samples with low Eu 2 O 3 contents (x ≤ 1 mol%) are amorphous while for higher europium oxide contents (x > 1 mol%) are glass cera- mics. They also reveal that increasing the Eu 2 O 3 content of samples the symmetry around the europium ions changes from face centered cubic to monoclinic. These symmetry changes are confirmed by the photo- luminescence data. In addition, photoluminescence data show that the co-doping with metallic copper nano- particles enhances the emission peaks of europium ions. UV-VIS absorption spectra show the presence of six coordinated copper (II) ions located at sites with a distorted octahedral symmetry. The EPR data confirm the presence of copper (II) ions in all the studied samples. Magnetic susceptibility measurements suggest the pre- sence of europium ions in both their 3+ and 2+ valence states and evidence an important clustering tendency of europium ions even for low Eu 2 O 3 contents. 1. Introduction Nowadays, lead-tellurite glasses and glass ceramics doped with rare earth ions cause a high interest due to their important properties such as their optical and electrical behavior [1–5], photoluminescence [6,7], low melting point and large thermal expansion coefficient [8,9], etc. In addition, the tellurite glass matrix has an interesting vitrogenic ability leading to multiple glass or glass-ceramic structures [10]. These reasons explain the intense use of tellurite materials doped with rare-earth ions for the production of sensors, color displays [11,12] and high definition TV screens [13,14], lasers, optical fibers and amplifiers [15–18], de- vices for biomedical diagnostics, etc. Since europium is one of the most utilized rare earths in such technologies, the study of luminescence properties of europium ions became very important. These properties are based on f-f type transitions of the electrons. Some recent studies shown that addition of copper nanoparticles to the glass matrix may enhance the luminescence of rare earth ions [19] and also may induce antibacterial and antifungal properties [20]. In this article we report the preparation of new lead-tellurite glass ceramics doped with europium ions and co-doped with copper nano- particles or copper ions. Their structural, optical, luminescence and magnetic properties were studied by using X-ray diffraction (XRD), UV- VIS, EPR and luminescence spectroscopies and density and magnetic susceptibility measurements. The goal was to obtain information con- cerning the influence of the dopant level (europium) and the co-dopant nature (cooper ions or copper nanoparticles) on both structural and behavioral properties of the studied lead-tellurite glass ceramics. 2. Experimental Samples of the (Eu 2 O 3 ) x ·(TeO 2 ) 80 ·(PbO) (19.7-x) ·(CuNPs) 0.3 (noted EuTePbCuNPs) and (Eu 2 O 3 ) x ·(TeO 2 ) 80 ·(PbO) (19.7-x) ·(CuO) 0.3 (noted https://doi.org/10.1016/j.jnoncrysol.2018.10.031 Received 1 September 2018; Received in revised form 22 October 2018; Accepted 23 October 2018 ⁎ Corresponding author. E-mail addresses: Eugen.Culea@phys.utcluj.ro (E. Culea), Petru.Pascuta@phys.utcluj.ro (P. Pascuta). Journal of Non-Crystalline Solids 505 (2019) 9–17 0022-3093/ © 2018 Elsevier B.V. All rights reserved. T