JOURNAL OF RARE EARTHS, Vol. 31, No. 7, July 2013, P. 685 * Corresponding author: S. Hraiech (E-mail: sanahraiech@gmail.com; Tel.: +216-79 32 52 50) DOI: 10.1016/S1002-0721(12)60343-3 Structural and optical studies of Yb 3+ , Er 3+ and Er 3+ /Yb 3+ co-doped phosphate glasses S. Hraiech 1,* , M. Ferid 1 , Y. Guyot 2 , G. Boulon 2 (1. Physical Chemistry Laboratory of Mineral Materials and Their Applications, National Center of Research in Materials Science, Technologic Park of Borj Cedria B.P. 73, 8020 Soliman, Tunisia; 2. Physical Chemistry of Luminescent Materials (LPCML), University of Lyon, Claude Bernard/Lyon 1 University, UMR 5620 CNRS, La Doua, 69622 Villeurbanne, France) Received 18 January 2013; revised 16 May 2013 Abstract: Phosphate glass samples with various Yb 2 O 3 and Er 2 O 3 contents were synthesized by the conventional melt quenching technique and characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy. The absorption, emission spectra and fluorescence decay studies were carried out both at low and room temperatures. Results showed the existence of several sites occupied by the rare earth ions in the phosphate glass. Up-conversion and cooperative fluorescence were also discussed. Keywords: Yb 3+ /Er 3+ co-doped; phosphate glass; energy transfer; upconversion; co-operative fluorescence; rare earths In recent years, glasses doped with rare-earth ions have drawn much attention due to their potential applica- tions in solid-state lasers, optical amplifiers and three- dimensional displays [1–4] . Recently, phosphate glasses have received a great deal of attention due to their poten- tial applications in optical data transmission, detection, sensing and laser technologies [5] . Among different glass hosts such as silicate, borate, etc., phosphate glasses have their unique characteristics that include high transpar- ency, low melting point, high thermal stability, high gain density that is due to high solubility for lanthanide (Ln) ions, low refractive index and low dispersion [6,7] . Among rare earth ions, attention has been focused on Yb 3+ and Er 3+ ions. Among rare earth ions, attention has been focused on Yb 3+ and Er 3+ ions. Yb 3+ ion has high quantum yield, strong mission intensity in the NIR do- main, and long fluorescence lifetime. Erbium doped glasses have been widely employed for several optical applications, especially in the field of optical amplifiers for fiber communications [8] and eye-safe lasers [9,10] . In addition, when the host is doped with Yb 3+ /Er 3+ couple, visible up-conversion emissions can be enhanced due to higher absorption cross section of Yb 3+ and energy transfer processes from Yb 3+ to Er 3+ ions [11–15] . Intense studies have been carried out upon Yb 3+ doped, Er 3+ doped and Yb 3+ /Er 3+ co-doped phosphate [16–18] , borogermanate [19] and tellurite [20] glasses. In this work, the Yb 3+ , Er 3+ and Er 3+ /Yb 3+ co-doped phosphate glasses were prepared, and the infrared ab- sorption, Raman, upconversion and cooperative fluores- cence, as well as the energy transfer processes, of the RE ions were studied. 1 Experimental All samples were prepared from the starting chemical constituents Na 3 P 3 O 9 , B 2 O 3 , Yb 2 O 3 and Er 2 O 3 (all from Aldrich 99.99% pure). One un-doped sample, four sam- ples doped with 0.5 mol.%, 1.0 mol.%, 1.5 mol.% and 2 mol.% of Yb 2 O 3 . Another three samples were prepared for 0.5 mol.%, 1.0 mol.% and 1.5 mol.% of Er 2 O 3 and three samples co-doped with 0.5 mol.% of Er 2 O 3 and 0.5 mol.%, 1.0 mol.% and 1.5 mol.% of Yb 2 O 3 . Calculated quantities of the chemical components were mixed and melted in an electric furnace at 900 °C for 2 h in plati- num crucibles so that a homogeneously mixed melt was obtained. The melts was then cast into a steel mould which was annealed at 300 °C; the glass was cooled slowly at room temperature. The amorphous nature of the glasses was confirmed through X-ray diffraction (XRD) studies by a BRUKER ® D8 Advance diffractometer equipped with a goniometer with geometry BRAGG-BRENTANO using Cu Kα ra- diation (λ=0.15406 nm). FT-IR has been a powerful tool to characterize phosphate glasses. FTIR spectra of the glasses were recorded with a NICOLET 560 spectrometer in the wavenumber range 400–1400 cm –1 at room temperature. Sample pellets were prepared by mixing and grinding a small quantity of glass powder with KBr powder and then compressing the mixtures to form thin pellets for testing. All measure- ments were run at 1 cm −1 resolutions.