Radiative and non radiative spectroscopic properties of Er 3+ ion in tellurite glass G.A. Kumar a , E. De la Rosa b, * , H. Desirena b a Department of Materials Science and Engineering, Rutgers-The State University of New Jersey, 607 Taylor Road, Piscataway, NJ 08854, USA b Centro de Investigaciones en Optica, Advanced Photonics Materials Lab (APML), Lomas del Bosque 115, A.P. 1-948, Leo ´ n Gto 37160, Mexico Received 28 June 2005; received in revised form 13 October 2005; accepted 26 October 2005 Abstract We have investigated in detail the mechanism of infrared emission and upconversion emission of Er 3+ in tellurite glass as a function of the dopant concentration. Both the infrared and upconversion emissions are competing processes and the efficiency of infrared emission at 1534 nm is 100% at the lowest Er content (0.5 mol%) and reduces to 50% at higher dopant concentration (>2 mol%). The green upcon- version emission at 548 nm is mainly due to the excited state absorption (ESA) from 4 I 11/2 , which populate the 4 F 7/2 level. In addition to this, the possible energy transfer (ET) through Er 3+ ( 4 I 11/2 ) + Er 3+ ( 4 I 11/2 ) ! Er 3+ ( 4 F 7/2 ) + Er 3+ ( 4 I 15/2 ) can also results in the green emis- sion as is noticed from the concentration dependent efficiency change of the green emission. The fluorescence quenching of green emis- sion with Er concentration may be related with the cross relaxation (CR) process 2 H 11/2 + 4 I 15/2 ! 4 I 9/2 + 4 I 13/2 . The red emission is due to the combined effect of the ESA from level 4 I 13/2 to 4 F 9/2 , the energy transfer process described by Er 3+ ( 4 I 13/2 ) + Er 3+ ( 4 I 11/2 ) ! Er 3+ ( 4 F 9/2 ) + Er 3+ ( 4 I 15/2 ) and the cross relaxation process. Ó 2005 Elsevier B.V. All rights reserved. Keywords: Upconversion; Tellurite glass; Spectroscopy; Er 3+ ; Luminescence; Judd–Ofelt theory; Visible emission 1. Introduction Trivalent Er is well know for its potential applications in many photonics devices including fiber amplifiers, lasers, display, data storage, biomedical imaging, etc. [1–8]. With the high demand for high transmission capacity wavelength division multiplexing (WDM), Er 3+ doped tellurite glasses and tellurite based fiber amplifiers have attracted consider- able attention [9,10]. Tellurite glass, because of its high density, mechanical strength, thermal stability, and chemi- cal durability has been considered as a suitable host for rare earth from many years back [11]. It has the lowest maximum phonon energy among oxide glasses and the largest refractive index values, both of which are beneficial for high radiative transition rates of rare earth ions [12,13]. Since both the 1534 nm and the visible upconversion emis- sions in Er 3+ are competing processes a systematic study is needed to understand the relationship between two in terms of the dopant concentration and the pump power, both of which are the controlling factors of the emission. In this sense, the aim of the present work is to characterize the infrared and upconversion spectral properties of Er 3+ in tellurite glass as a function of the Er 3+ concentration and determine the optimum concentration to obtain the highest quantum efficiency. 2. Experimental 2.1. Sample preparation The glass compositions employed were 75TeO 2 – (15  x)ZnO–10Na 2 O–xEr 2 O 3 (x = 0.5, 1, 2, 3). All samples were prepared from the starting chemical constituents TeO 2 , ZnO, Na 2 O and Er 2 O 3 (all from Aldrich 99.99% pure). Calculated quantities of the chemicals were mixed 0030-4018/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2005.10.081 * Corresponding author. Tel.: +52 477 441 4200; fax: +52 477 441 4209. E-mail address: elder@cio.mx (E. De la Rosa). www.elsevier.com/locate/optcom Optics Communications 260 (2006) 601–606