Journal of Alloys and Compounds 490 (2010) 184–189 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Spectroscopic studies of the Pr 3+ -doped borovanadate glass M. El Okr a , M. Farouk a,∗ , M. El-Sherbiny a , M.A.K. El-Fayoumi b , M.G. Brik c a Department of Physics, Faculty of Science, Al Azhar University, Cairo 11884, Egypt b Department of Physics, Faculty of Science, Beni-Sueif University, Egypt c Institute of Physics, University of Tartu, Riia 142, Tartu 51014, Estonia article info Article history: Received 24 June 2009 Received in revised form 8 July 2009 Accepted 8 July 2009 Available online 18 July 2009 Keywords: Rare earth doped glasses Judd–Ofelt theory abstract Praseodymium-doped borovanadate glasses were prepared by conventional quenching melt technique. The prepared composition was [90 Na 2 B 4 O 7 –(10 - x)V 2 O 5 –x Pr 6 O 11 ], x =0, 0.5, 1, 2, 4, 6, 8 and 10mol%. Optical absorption spectra have been investigated in the spectral range from 195 to 2500 nm. Experimental oscillator strengths of the observed bands have been estimated and used for calculating the Judd–Ofelt (JO) intensity parameters. Radiative transition probabilities as well as branching ratios were calculated. The radiative lifetime of the 1 D 2 and 3 P 0 levels was varied from ca. 344 to 808 s and ca. 30 to 63 s respectively. The optimum Pr concentration at which the branching ratios have the maximum values was obtained at 1 mol%. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Rare earth (RE) doped crystals and glasses are widely studied due to numerous applications of these systems (active media for solid state lasers, optical telecommunication, non-linear optical materials, etc.) ([1,2] and references therein). A very attractive fea- ture of the RE ions is that they have a large number of energy levels in the infrared, visible and ultraviolet spectral domains. Positions of the energy levels arising from the 4f electronic configurations of RE ions are slightly influenced by the environment due to the screening effects produced by the completely filled outer 5s and 5p electron shells. Among the RE ions, Pr 3+ ion is of particular interest, since its electron configuration (4f 2 ) is, on one hand, quite simple, and, on the other hand, it gives rise to a number of energy levels in a rather wide spectral region from near infrared to ultraviolet. In addi- tion, its energy level scheme allows for efficient energy transfer and up conversion processes, thus enlarging the possible areas of Pr 3+ applications. Many spectroscopic studies on Pr 3+ activated crys- tals and glasses have been reported in literature by several authors [3–12]. The Judd–Ofelt (JO) [13,14] theory has been proved to be a powerful tool which is widely used for an analysis of the optical spectra of RE ions in various media. The three JO intensity parameters ˝  ( = 2, 4, 6) depend on chemical bonding between the RE ions and their nearest envi- ronment. These parameters (from the physical reasons) should be positive, but quite often the second rank intensity parameter ˝ 2 ∗ Corresponding author. Tel.: +20 2 22615836; fax: +20 2 22629356. E-mail address: mf egypt22375@yahoo.com (M. Farouk). was reported to have a negative value, which is uncommon and physically meaningless within the frame of JO theory [15,16]. The main reason for such a non-physical result is the noticeable mix- ture of the 4f and 5d electronic configurations (for Pr 3+ the lowest 5d level lies at about 33,000 cm -1 ). To overcome this problem, some modifications of the conventional JO theory were suggested, related either to inclusion of a correction related to the 5d configuration [17,18], or calculations of the odd rank intensity parameters [19,20]. The present work aims to study the dependence of the experimen- tal absorption spectra and radiative transition probabilities in the borovanadate glass on varying Pr 3+ concentration. The phenomeno- logical intensity parameters ˝ 2 , ˝ 4 and ˝ 6 were determined using the least square fitting procedure. The values obtained were used to calculate the lifetimes of the Pr 3+ excited levels and the branching ratios of the photoluminescence transitions, in order to determine the optimized level of Pr 3+ concentration. 2. Sample preparation and absorption spectra measurements Alkali borovanadate glasses with the molar compositions of [90 Na 2 B 4 O 7 –(10-x)V 2 O 5 –x Pr 6 O 11 ], x =0.5, 1, 2, 4, 6, 8 and 10mol% were prepared. Approximately 25 g of the batch chemical composi- tion was mixed in an agate mortar and melted in a porcelain crucible at 1150 ◦ C for 2 h in an electrical furnace. The melt was poured onto a preheated brass plate and pressed with another brass plate. The obtained glasses were annealed at 350 ◦ C for 3 h to remove mechanical stress. After annealing, they were polished and the opti- cal absorption spectra were recorded in the spectral range from 195 to 2500nm using the JASCO – V570 spectrophotometer. 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.07.059