Enhanced spatial energy transfer in Er-doped silica glasses F.A.M. Marques a, * , A.F.G. Monte a , E.O. Serqueira a , P.C. Morais b , N.O. Dantas a a Universidade Federal de Uberlândia, Instituto de Física, Uberlândia MG 38400-902, Brazil b Universidade de Brasília, Instituto de Física, Núcleo de Física Aplicada, Brasília DF 70910-900, Brazil article info Article history: Received 29 July 2009 Received in revised form 16 April 2010 Accepted 18 April 2010 Available online 21 May 2010 Keywords: Energy transfer Silica glasses Erbium Microluminescence abstract Energy transfer processes and the related photon diffusion have been investigated in Er-doped silica glasses. The spatial distribution of the luminescence on the sample surface was scanned by the spa- tially-resolved microluminescence technique for several samples with different Er 3+ -ion concentrations. Efficient long-range photon diffusion for the 1.54 lm emission was found at 1.85 wt.%. We propose an energy transfer process between erbium ions randomly distributed throughout the glass medium. Each ion acts as absorbers and emitters in such a way that the energy is spatially transferred. Ó 2010 Elsevier B.V. All rights reserved. 1. Introduction The addition of some impurities in glass matrix has attracted many studies due to wide advanced applications. Silica glasses have been shown to be highly versatile for rare-earth host [1]. The intra-4f-shell transitions from Er 3+ are responsible of a strong luminescence at 1.54 lm which is an interesting wavelength for transmissions in silica-based optical fibers. Erbium-doped fiber amplifiers are essential to the expansion and development of the worldwide telecommunications network since they provide the means of amplifying signals in optical fibers at 1.5 lm telecommu- nications band [2,3]. In addition, the coherence properties of er- bium materials may enable all-optical signal routing, correlating, and processing at 1.5 lm to provide new capabilities and enhanced performance for the telecommunications industry. Rare-earth doped glasses have demonstrated technological interest, aiming optical device applications, such as active media for solid-state la- sers and optical amplifiers [4–8]. In this paper, the energy transfer process has been studied for Er-doped silica glasses as a function of Er 3+ concentration. This pro- cess was studied by scanning the 4 I 13/2 ? 4 I 15/2 transition of micro- luminescence (ML) at 1.54 lm [9]. The dependence of the photon effective diffusion length (L eff ) on the Er 3+ -ion concentration dem- onstrates that an optimum value for L eff can be obtained. The latter corresponds to the most efficient value for photon travelling in Er 3+ -doped silica glasses. We have found that 1.85 wt.% of Er 2 O 3 corresponds to the best concentration for 1.54 lm photon diffusion process. Hence, using this concentration the Er 3+ -doped glasses would be more promising for optical amplifiers. We have carried out an experimental investigation of Er 3+ - doped silica glasses in order to evaluate the photon diffusion mechanisms and the strength of the coupling between Er 3+ -ions by analyzing the spatially-resolved microluminescence on the sample surface. To perform this study various samples of Er 3+ - doped silica glasses were synthesized as a function of the doping concentration. The spatial distribution of the luminescence was studied and the energy transfer processes among Er 3+ -ions were discussed. 2. Sample preparation and experimental details The glass matrix used in this study was synthesized with 40 SiO 2  30 Na 2 CO 3  20 PbO  10 ZnO (mol%). Each compound was added for a specific purpose: SiO 2 as glass former, Na 2 CO 3 to re- duce the melting point, PbO to increase the refraction index, and ZnO as intermediate oxide. The glass matrix acts as a host for Er 3+ -ions [10]. Afterwards, x wt.% of Er 2 O 3 was added to the glass matrix, were x is ranging from 0.1 to 2.5. The mixture was melted in porcelain crucible at 1000 °C for 30 min. Then, the samples were cooled down to room temperature and later on annealed at 350 °C for 3 h in order to release thermal stress. Samples were properly polished for optical measurements. A microluminescence system was coupled to a variable temper- ature cryostat for low-temperature measurements. The photolumi- nescence (PL) measurements were recorded with an Ar + -ion laser as excitation source. The luminescence from the sample was 0925-3467/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2010.04.028 * Corresponding author. Address: F.A.M. Marques, Universidade Federal de Uberlândia, Instituto de Física, Bloco X, Sala 1X08, Uberlândia MG 38400-970, Brazil. Tel.: +39 32 77 63 96 48; fax: +55 34 32 39 41 90. E-mail address: flaviofisica@gmail.com (F.A.M. Marques). Optical Materials 32 (2010) 1248–1250 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat