Characterization of Eu 3+ -doped fluorophosphate glasses for red emission R. Balakrishnaiah a , R. Vijaya a , P. Babu b , C.K. Jayasankar a, * , M.L.P. Reddy c a Department of Physics, Sri Venkateswara University, Tirupati 517 502, India b Department of Physics, Government Degree College, Wanaparthy 509 103, India c Regional Research Laboratory, C.S.I.R., Thiruvananthapuram 695 019, India Available online 26 March 2007 Abstract Fluorescence spectra and decay curves of the 5 D 0 level for different concentrations of Eu 3+ (4f 6 ) ions in K–Ba–Al fluorophosphate glasses have been measured at room temperature and are analyzed. The Judd–Ofelt intensity parameters X 2 and X 4 have been determined from the intensity ratios of emission peaks corresponding to 5 D 0 ! 7 F J (J = 2 and 4) to 5 D 0 ! 7 F 1 transitions for 1.0 mol% glass. The intensity parameters thus obtained are in turn used to calculate the radiative properties of the fluorescent levels of Eu 3+ ions. Second and fourth rank crystal-field parameters have been evaluated by assuming a C 2V site symmetry for the local environment of Eu 3+ ions to estimate the crystal-field strength experienced by Eu 3+ ions in the present host. The decay profiles of the 5 D 0 ! 7 F 2 transition of Eu 3+ ions in the present glasses are found to be single exponential for all the studied Eu 3+ ion concentrations. A marginal increase in lifetime of the 5 D 0 level has been noticed with Eu 3+ ion concentration up to 2.0 mol% and then the lifetime marginally decreases for higher Eu 3+ ion concentrations. Ó 2007 Elsevier B.V. All rights reserved. PACS: 79.60.Ht; 78.55.Àm; 71.70.Ch; 42.70.Ce Keywords: Optical properties; Luminescence 1. Introduction Alkali aluminometaphosphate glasses are the promising hosts among oxide glasses for lanthanide (Ln) ions due to their relatively higher refractive indices, lower dispersion, larger stimulated emission cross-sections, higher gain, bet- ter chemical durability and lower thermo-optical qualities when compared with many other hosts such as silicates [1]. They are very easy to prepare in various compositions in bulk form and they preserve useful properties upon the introduction of a significant amount of Ln ions. Addition of fluoride contents will further improve the radiative prop- erties by reducing the number of hydroxyl (OH À ) groups in the glass network [2]. Among Ln ions, trivalent europium (Eu 3+ ) ion is the best candidate to be used as a probe to investigate the local structure around Ln ions in condensed matter. This is because, the low lying energy level scheme of Eu 3+ ions is simple and the transition between 7 F 0 and 5 D 0 non-degen- erate levels is convenient to apply the fluorescence line nar- rowing technique to analyze changes from site to site through energy level scheme analysis [3]. Also Eu 3+ -doped materials are frequently used in photonic applications as red phosphors for field emission technology due to the nar- row and monochromatic emitting nature of the 5 D 0 ! 7 F 2 transition of Eu 3+ ions at 610 nm. The present work reports the fluorescence and local field properties of differ- ent concentrations of Eu 3+ ions in K–Ba–Al fluorophos- phate glass. 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.10.063 * Corresponding author. Tel.: +91 877 2248033; fax: +91 877 2225211. E-mail address: ckjaya@yahoo.com (C.K. Jayasankar). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 1397–1401