Physica E 38 (2007) 144–147 Non-radiative sub-microsecond recombination of excited Er 3+ ions in SiO 2 sensitized with Si nanocrystals I. Izeddin a,Ã , T. Gregorkiewicz a , M. Fujii b a Van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65, NL-1018XE Amsterdam, The Netherlands b Department of Electrical and Electronic Engineering, Faculty of Engineering, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan Available online 22 December 2006 Abstract Temporal aspects of recombination and energy transfer processes in Er-doped SiO 2 sensitized with Si nanocrystals (Si-nc’s) were investigated by luminescence and excitation spectroscopy using time-correlated photon counting. This detection mode allows that emissions of very different intensities and dynamics may be investigated simultaneously, without loss of time resolution or amplitude deformation. In this way, components with decay constants ranging from nano- to milliseconds were identified in the luminescence bands of Si-nc’s, Er 3+ ions, and defects. We postulate to relate these to recombination processes originating from isolated Er 3+ ions and Er 3+ ions located inside or in direct vicinity of Si-nc’s, with dynamics in the milli- and microsecond, and nanosecond range, respectively. In this way, a unique picture of the mutual relation between the two subsystems of Er 3+ ions and Si-nc’s, and truly microscopic information on the sensitization effect is obtained. Based on this new information, we conclude on a strong enhancement of non-radiative recombination of Er 3+ upon sensitization with Si-nc’s and put forward a complete description of Si-nc’s as sensitizers of SiO 2 :Er system, where all the Er 3+ ions available in the system are accounted for. r 2007 Elsevier B.V. All rights reserved. PACS: 78.55.m; 31.70.Hq; 78.67.Bf; 81.07.Bc Keywords: Nanocrystals; Si; Excitation processes; Recombination; Photoluminescence 1. Introduction Recently, it has been shown that photo- and electro- luminescence of Er 3+ ions in SiO 2 can be effectively sensitized with Si nanocrystals (Si-nc’s) which enable indirect excitation of Er 3+ ions [1,2]. This process is non- resonant and relatively efficient, with an (effective) excita- tion cross-section of sE10 17 –10 16 cm 2 , which repre- sents an increase by a factor of 10 3 [3,4]. These promising characteristics have risen considerable hopes on possible applications of the SiO 2 :Er+Si-nc for Si photonics and specific devices have been proposed [5–7]. The prospects are however discouraged by recent multiple reports that only a very minor part of all Er 3+ dopants can be excited via Si-nc’s [8,9]. Moreover, it turns out that upon doping with Si-nc’s a very significant loss of the optical activity of Er 3+ occurs, so that even upon resonant excitation directly into one of the higher Er 3+ states, only a small part of Er (o10%) contributes to the emission of 1.5 mm photons. Here, we investigate this apparent loss of optical activity and demonstrate that introduction of Si-nc’s also opens an efficient channel of non-radiative recombination. 2. Experimental A series of Si-nc- and Er-doped SiO 2 2 mm layers were prepared by radio frequency co-sputtering on an SiO 2 substrate. The samples were characterized by different concentrations of Er dopant and size and concentration of Si-nc’s. Details of the sample preparation procedure can be found elsewhere [10,11]. By emission spectroscopy, a particular sample with the most intense 1.5 mm Er-related emission was chosen for detailed investigation of emission ARTICLE IN PRESS www.elsevier.com/locate/physe 1386-9477/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2006.12.045 Ã Corresponding author. E-mail address: izeddin@science.uva.nl (I. Izeddin).