Optical and physical properties of Er 3+ -doped oxy-fluoride tellurite glasses E.F. Chillcce a,⇑ , I.O. Mazali b , O.L. Alves b , L.C. Barbosa a a Instituto de Física GlebWataghin, Universidade Estadual de Campinas-UNICAMP, Campinas, SP 13083-970, Brazil b Instituto de Química, Universidade Estadual de Campinas-UNICAMP, Campinas, SP, Brazil article info Article history: Received 10 July 2010 Received in revised form 21 September 2010 Accepted 27 September 2010 Available online 20 October 2010 Keywords: Oxy-fluoride tellurite glass Optical and physical properties Thermal stability Rayleigh scattering loss Erbium-ion emission cross section properties abstract In this manuscript we present the effects of ZnF 2 concentration on the optical and physical properties of Er 3+ -doped oxy-fluoride tellurite glasses (7500 ppm Er 2 O 3 -(80x)TeO 2 -xZnF 2 -20ZnO, where x = 5, 10, 15, 20, 25 and 30 mol%). In general, as the concentration of ZnF 2 increases: (i) the thermal stability, the opti- cal transparency window, and the lifetime of the 4 I 13/2 level increase; (ii) the density, the linear refractive index, the Rayleigh scattering loss, and the OH  ion concentration decrease; and (iii) the Er 3+ ion emission cross section spectrum is quenched and the bandwidth is reduced. The 4 I 13/2 level lifetime increase may be associated with the luminescence re-absorption and the radiative transition ( 4 S 3/2 ? 4 I 13/2 ) processes, since both processes may contribute to the 4 I 13/2 level population. The Er 3+ ion emission cross section spectrum (at around 1550 nm) of oxy-fluoride tellurite glass containing 30 mol% of ZnF 2 was very similar to those of Fluoride glasses. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction Tellurite glasses present interesting and important optical prop- erties such that interest in their potential applications has in- creased considerably over the last few years. Indeed, numerous devices including optical amplifiers (based on Raman and Brillouin effects), planar waveguides and nanowires have been fabricated using tellurite glasses [1–6]. One of the main problems concerning the use of this kind of material in optical fiber applications has been its high optical attenuation (>1 dB/m), although an optical fi- ber based on TeO 2 -Bi 2 O 3 -ZnO-Na 2 O glass has been recently re- ported with an attenuation of 20 dB/km [7]. On the other hand, rare earths show very high solubility in tellurite glasses [8], and this allows the material to be co-doped with several rare earths simultaneously [9]. In this context, tellurite fibers co-doped with Er 3+ and Tm 3+ ions show broadband emission spectra with band- widths of 160 nm around the 1550 nm band [10]. Unfortunately, the lifetime of the 4 I 13/2 ? 4 I 15/2 transition correlated with this broadband is associated with energy transfer from (Er 3+ ) 4 I 13/2 and (Tm 3+ ) 3 F 4 levels [11], and the lifetime is short in glasses co- doped with these rare earths. Although the deleterious effect of this energy transfer mechanism cannot be avoided, the lifetime of the 4 I 13/2 ? 4 I 15/2 transition may be increased in order to enhance the efficiency of optical fiber devices within the optical communication window. Indeed, optical fiber amplifiers with long 4 I 13/2 level lifetimes could be used as active systems because they present low power saturation [12], avoiding up-conversion processes. The lifetime of the 4 I 13/2 level may be increased by reducing the OH  ions content in the tellurite glass matrix. This OH  ions reduc- tion was made possible by injecting oxygen gas during the melting process [13–15]. Since many of the OH  overtones around the 1550 nm band coincide with the 4 I 13/2 ? 4 I 15/2 transition of Er 3+ - ions, the depletion of OH  ions causes a reduction in the energy transfer between (Er 3+ ) 4 I 13/2 and OH  . An alternative method to increase the lifetime of the 4 I 13/2 level involves the introduction of high concentrations of ZnF 2 in the glass matrix. It was originally reported that tellurite glasses doped with high concentrations of ZnF 2 presented long lifetimes of transitions between Nd 3+ -ion lev- els [16,17]. Subsequently, it was found that the lifetimes of transi- tions between Er 3+ ion levels in Er 3+ -doped tellurite glasses were also long due to the high concentrations of ZnF 2 [18,19]. In general, the lifetime of the 4 I 13/2 level is mainly influenced by the following mechanisms: (i) the up-conversion processes related to the pump laser power [20], (ii) the red-shift or the re-absorption processes related to the fiber length [21], and (iii) the band broad- ening (or narrowing) caused by the change in the environment of the Er 3+ ions distributed within the glass structure [13]. It is well-known that Er 3+ -doped oxy-fluoride tellurite glasses containing high concentrations of ZnF 2 present: (i) a low density, (ii) a low linear refractive index, (iii) a low OH  ions concentration, (iv) a long 4 I 13/2 level lifetime, and (v) a wider transparency 0925-3467/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2010.09.027 ⇑ Corresponding author. Tel.: +55 19 3521 4135; fax: +55 19 3521 5428. E-mail address: chillcce@ifi.unicamp.br (E.F. Chillcce). Optical Materials 33 (2011) 389–396 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat