Structural and luminescence behavior of lead fluoroborate glasses containing Eu 3 þ ions S. Arunkumar a , K. Venkata Krishnaiah b , K. Marimuthu a,n a Department of Physics, Gandhigram Rural University, Gandhigram 624302, India b Department of Physics, Sri Venkateswara University, Tirupati 517502, India article info Article history: Received 29 December 2012 Received in revised form 12 February 2013 Accepted 13 February 2013 Available online 24 February 2013 Keywords: Raman spectra Phonon side band Judd–Ofelt parameters Branching ratios Stimulated emission cross-section Lifetime abstract Structural and luminescence behavior of lead fluoroborate glasses prepared with the chemical composition (50 x)B 2 O 3 þ20PbO þ20PbF 2 þ10ZnOþxEu 2 O 3 (where x ¼0.05, 0.1, 0.5, 1, 2 and 3 in wt%) have been studied by varying the trivalent europium ion content. Structural behavior of the prepared glasses has been explored through XRD, FTIR and Raman spectral analysis. Optical characterization has been made using UV–vis–NIR absorption, excitation, luminescence and decay curves of the present glasses. Through the absorption spectra, bonding parameters ( b and d) have been determined and the positive value of d indicates the covalent nature. The band gap values are found to decrease with increasing Eu 3 þ ion concentration whereas Urbach’s energy values are found to increase. The PSB associated with the 7 F 0 - 5 D 2 excitation transition is used to determine the electron–phonon coupling constant and the local structure of the Eu 3 þ ions with its surrounding ligands. The luminescence intensity ratio of the 5 D 0 - 7 F 2 to 5 D 0 - 7 F 1 transition has been calculated to estimate the local site symmetry around the Eu 3 þ ions. Judd–Ofelt (J–O) intensity parameters O l (l ¼2,4,6) were obtained from the emission spectra and the same is used to estimate the transition probability (A), stimulated emission cross-section ðs E P Þ and branching ratios (b R ) for the excited levels of the Eu 3 þ ions. The decay profiles were found to be single exponential for all the title glasses. The higher values of A, s E P and b R corresponding to the 5 D 0 - 7 F 2 emission level at 614 nm confirm the potential of the present glasses as a red laser active medium. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Over the past few decades, research on structural and optical properties of rare earth (RE) doped oxyfluoride glasses gained lot of interest due to their technological applications in the field of photonics and optoelectronics, as display devices, optical ampli- fiers, laser materials, sensors, high density optical memory devices, solid state lasers and amplifiers for fiber-optic commu- nication [1,2]. In addition to that, glasses containing heavy metal oxides (HMO) such as Pb, Cd and Bi have also become of vital importance due to their low phonon energies, high refractive indices, low transition temperature, high polarizability and good rare-earth ions solubility and hence it significantly increases the optical and electronic properties such as radiative properties, quantum efficiencies and electrical conductivity of these glasses [3,4]. Further, fluoride glasses offer lower phonon energy than oxide matrices, whereas the oxide matrices possess advantages like higher mechanical strength, chemical durability and thermal stability [5]. In general, host glasses with low phonon energy provide less non-radiative relaxation rates and high quantum efficiencies. Transparent oxyfluoride glasses combine the advan- tages of both the fluoride and oxide matrices and are considered to be a good choice as hosts for RE ions and thus turned to be one of the most promising optical materials. Among the lanthanides, trivalent europium ion Eu 3 þ has been chosen as a probe to explore the optical behavior of the lead fluoroborate glasses due to the fact that Eu 3 þ (4f 6 ) ion possess narrow band emission, almost monochromatic light and longer lifetime of the optically active state. Also the local structure around Eu 3 þ ions can be obtained from the f–f transition spectra. The non-degenerate 7 F 0 ground state and the 5 D 0 excited state of the Eu 3 þ ions are highly suitable for studying the symmetry and in-homogeneity in the host matrix [6,7]. The Eu 3 þ ions doped into several glasses and crystals have been investigated in order to obtain the strong red luminescent materials because of its hypersensitive radiative emission transition at 616 nm corre- sponding to the 5 D 0 - 7 F 2 transition and non-radiative emission transition at 593 nm corresponding to the 5 D 0 - 7 F 1 transition [8]. Thus the radiative to the non-radiative luminescence intensity ratio is widely used to investigate the chemical bond of anions Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physb.2013.02.022 n Corresponding author. Tel.: þ91 451 2452371; fax: þ91 451 2454466. E-mail address: mari_ram2000@yahoo.com (K. Marimuthu). Physica B 416 (2013) 88–100