Synthesis and luminescence investigation of Tb 3 þ –Yb 3 þ codoped CdF 2 single crystals A. Cheddadi a , H. Boubekri a , K. Labbaci a,b,c , M. Diaf a,n , L. Guerbous b , T. Duvaut c , J.P. Jouart c Q1 a Laboratory of Laser Physics, Optical Spectroscopy and Optoelectronics (LAPLASO), Badji Mokhtar Annaba University, POB 12, 23000 Annaba, Algeria b Laser Department, Nuclear Technique Division, Nuclear Research Center of Algiers, 02 Bd Frantz Fanon, 16000 Algiers, Algeria c ECATHERM/GRESPI, Reims Champagne-Ardenne University, France article info Article history: Received 15 April 2013 Received in revised form 7 November 2013 Accepted 1 December 2013 Keywords: CdF 2 Terbium Judd–Ofelt theory Optical absorption Terbium green emission Fluorescence decay abstract Tb 3 þ (1%), Yb 3 þ (5%):CdF 2 single crystals with good optical quality are grown by the standard Bridgman method. The crystal structure is checked by means of X-ray diffraction analysis. Absorption, excitation and fluorescence spectra are carried out at room temperature. The standard Judd–Ofelt (JO) model is applied to absorption intensities of Tb 3 þ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are Ω 2 ¼2.40, Ω 4 ¼2.03 and Ω 6 ¼3.60 in 10 –20 cm 2 units, with root mean square of δ ¼0.1  10 –20 cm 2 . These JO intensity parameters are then applied to determine the radiative transition probabilities (A JJ 0 ), radiative lifetimes (τ rad ) and branching ratios (β JJ 0 ) of Tb 3 þ transitions. We focused on the blue and green transitions from 5 D 3 and 5 D 4 levels which occur with relatively high transition probabilities and branching ratios. The fluorescence spectrum exhibits two groups of lines well resolved from 5 D 3 and 5 D 4 manifolds ( 5 D 3 , 5 D 4 - 7 F J , J ¼6, 5, 4, 3, 2). This spectrum is characterized by two strong lines corresponding to 5 D 3 - 7 F 5 (violet/blue line) and 5 D 4 - 7 F 5 (green line) transitions. For the main transitions, there is a good agreement between the fluorescence spectrum and the spontaneous emission probabilities given by the JO analysis. We also performed fluorescence decay spectra and measured the lifetime of 5 D 3 and 5 D 4 levels. This have led us to obtain the quantum efficiency of the two transitions 5 D 3 , 5 D 4 - 7 F 5 . For the green transition, the value of radiative quantum efficiency obtained is high, which reflects that multiphonon relaxation is limited. The reduced quantum efficiency of the transition from 5 D 3 manifold shows the happening of a cross relaxation process between Tb 3 þ ions as follows: 5 D 3 þ 7 F 6 - 5 D 4 þ 7 F 0 , because of the closely matched energy difference between ( 5 D 3 , 5 D 4 ), and ( 7 F 6 , 7 F 0 ) levels. These parameters suggest that the studied host has the potential to produce intense green emission. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Fluoride materials, such as crystals or glasses, are of great impor- tance in the development of high performance new optical materials for visible and infrared optical applications, mainly due to their high transparency over a large electromagnetic domain and relatively low phonon energies. They have also the ability to incorporate rare earth ions as luminescent centers even in high concentrations. Doped with one or more rare earth, they show excellent optical properties varied enough that enable a lot of applications in various areas of every- day life such as laser technology, display panels, vacuum fluorescent displays, solar cells. MF 2 difluoride crystals (M¼ Alkaline earth element, Cd or Pb) with fluorite structure are of great interest as materials for photonics. Doped with trivalent rare earth ions, they are the basic materials for many applications in laser technology. The CdF 2 crystals occupy a specific place among those MF 2 crystals. They are transparent in the Near UV, visible and infrared electromagnetic domain and can exhibit semiconducting behavior under special conditions. CdF 2 and PbF 2 are used as main constituents of many fluoride glasses, material for laser arrays and infrared detectors and medium for optical information processing systems [1]. They are good competitors for this kind of applications [2]. Moreover, several reports have confirmed the use of trivalent terbium (Tb 3 þ , 4f 8 ) as an active ion in laser medium. In particular, there has been an interest in terbium for its stimulated green emission through the 5 D 4 - 7 F 5 (544 nm) transition. Among the other rare earths, terbium has been studied very little at first but in recent years it has been the subject of several studies which reported specially that it is used as a potential active element in mid- and far infrared laser and as a probe of cluster formation [3,4]. These studies also mentioned a room temperature pulsed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 Contents lists available at 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.2013.12.001 n Corresponding author. Tel.: þ213 551348316. E-mail address: diafma@yahoo.fr (M. Diaf). Please cite this article as: A. Cheddadi, et al., Physica B (2013), http://dx.doi.org/10.1016/j.physb.2013.12.001i Physica B ∎ (∎∎∎∎) ∎∎∎–∎∎∎