Thermal, chemical, optical properties and structure of Er 3+ -doped and Er 3+ /Yb 3+ -codoped P 2 O 5 –Al 2 O 3 –ZnO glasses S.W. Yung a, ⁎, S.M. Hsu b , C.C. Chang a , K.L. Hsu a , T.S. Chin c , H.I. Hsiang d , Y.S. Lai a a Department of Materials Science and Engineering, National United University, Miao-Li, 36003, Taiwan b Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung, Taiwan c Department of Materials Science and Engineering, Feng Chia University, Taichung, Taiwan d Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan abstract article info Article history: Received 29 June 2010 Received in revised form 26 November 2010 Available online 13 January 2011 Keywords: Phosphate glass; Er 3+ /Yb 3+ -codoping; Fluorescence; Absorption cross-section; Emission cross-section This study was explored in series of the optical, thermal, and structure properties based on 60P 2 O 5 –10Al 2 O 3 – 30ZnO (PAZ) glasses system that doped with varied rare-earth (RE) elements Yb 2 O 3 /Er 2 O 3 . The glass transition temperature, softening temperature and chemical durability were increased with RE-doping concentrations increasing, whereas thermal expansion coefficient was decreased. In the optical properties, the absorption and emission intensities also increase with RE-doping concentrations increasing, When Er 2 O 3 and Yb 2 O 3 concentrations are over than 3 mol% in the Er 3+ -doped PAZ system and Yb 3+ -doped concentration is over than 3 mol% for Er 3+ /Yb 3+ -codoped PAZ system, the emission intensity significantly decreases presumably due to concentration quenching, formation of the ions clustering, and OH - groups in the glasses network. It is suggested that the maximum emission cross-section (σ e ) is 7.64×10 -21 cm 2 at 1535 nm is observed for 3 mol% Er 3+ -doped PAZ glasses. Moreover, the maximum σ e × full-width-at-half-maximum is 327.8 for 5 mol% Er 3+ -doped PAZ glasses. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Phosphate glasses have lower glass transition temperature (T g ), lower melting temperature (T m ), higher thermal expansion coeffi- cients (α)[1–3], lower optical dispersions, and good UV transparency than most silicate glasses[4,5]. These properties make them suitable for many applications, such as waveguide amplifier [5], specialty sealing [6], nuclear waste glasses [7,8] and laser applications [5,9]. However, these glasses have a relatively poor chemical durability that often limits their usefulness [10,11]. According to previous studies, the chemical durability of phosphate glasses can be improved by the addition of various rare-earth ions such as Er 3+ and Yb 3+ ions [12,13]. Rare-earth doped phosphate glasses have been extensively investigated in recent years. In particular, erbium-doped phosphate glasses are interesting materials for amplifiers, wavelength division multiplexing and optical communication systems at 1.5 μm [14–16]. The energy levels of the Er 3+ ions for optical amplification at 1.5 μm form a three-level system which requires a high pump rate to achieve population inversion. On the other hand, the concentration of Er 3+ in the glass must be as higher as possible [17]. However, the higher non- radiative losses incur when Er 3+ concentration is beyond a critical value. In addition, the pumping efficiency and absorption cross- section of Er 3+ in glasses are rather low. Therefore, codoping with sensitizer ions is usually required [18]. Yb 3+ is a well-known sensitizer to enhance the absorption and pumping efficiency of Er 3+ doped phosphate glasses, due to the fact that 2 F 7/2 → 2 F 5/2 transition in spectral region of the Yb 3+ overlaps the 4 F 15/2 → 4 F 11/2 transition of the Er 3+ . Such an effective transfer of the excitation energy prevails from ytterbium to erbium [19,20]. At the same time, Yb 3+ ions exhibit high stimulated emission cross-section and a broad absorption band between 800 and 1100 nm [21]. Zhang et al. studied spectroscopic properties and energy transfer in Er 3+ /Yb 3+ -doped phosphate glasses [22]. They indicated that the intensity of fluorescence emission of Er 3+ /Yb 3+ -codoped phosphate glass is much higher than that of Er 3 single-doped phosphate glass. Chen et al. indicated that the Yb 3+ ions can absorb more efficiently the 980 nm light and transfer the energy to Er 3+ in heavily Er-doped silica optical fibers [23]. The phenomenon increases the population of 4 I 11/2 level and induces promotion of photo-luminescence efficiency at 1540 nm. However, in accordance with the literatures [12,23,24], excess rare-earth ions in many crystals, fiber amplifiers and glass systems causes the reduction of optical properties. This arises from two reasons, the concentration quenching and the formation of ions clustering. Therefore, the glass with optimum dopant concentration of rare-earth ions is very important. At present, several researches explored the effect of Er 3+ on optical properties and energy transfer. Up to now there are only a few researches of the effects of Er 3+ and Yb 3+ concentrations on optical properties and structure. The purposes Journal of Non-Crystalline Solids 357 (2011) 1328–1334 ⁎ Corresponding author. Tel.: + 886 37 382521. E-mail address: hwyang@nuu.edu.tw (S.W. Yung). 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.12.011 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol