Journal of Alloys and Compounds 408–412 (2006) 845–847 Effect of counter ions on the reduction process of Sm 3+ ions in TiO 2 –ZrO 2 –Al 2 O 3 –SiO 2 glasses Go Kawamura, Tomokatsu Hayakawa, Masayuki Nogami ∗ Department of Materials Science and Engineering, Nagoya Institute of Technology, Showa, Nagoya 466-8555, Japan Received 31 July 2004; accepted 25 November 2004 Available online 3 June 2005 Abstract The radio-chemical reaction of Sm 3+ reduction in xTiO 2 (ZrO 2 )–(10 - x)Al 2 O 3 –90SiO 2 glasses (x = 0–10 mol%) was examined by a photo- luminescence technique with fluorescence intensities at 560–650 nm (Sm 3+ ; 4 G 5/2 → 6 H J ) and 680–720 nm (Sm 2+ ; 5 D 0 → 7 F J ). It was found that the reduction of Sm 3+ ions by X-ray irradiation was significantly decreased by the introduction of TiO 2 and no reduction occurred in the glasses containing TiO 2 above 5%. On the other hand, in the ZrO 2 containing glasses, the reduction of Sm 3+ ions was almost monotonous up to 5% of ZrO 2 . Electron spin resonance (ESR) spectra revealed the presence of some defect centers; hole-trap center (HTC) and electron-trap center (ETC). Hole centers trapped by oxygen ions bound to the Al 3+ ions were strongly related to the reduction process from Sm 3+ to Sm 2+ ions; the released electrons from the Al-related HTC were captured by the nearest Sm 3+ ions, forming Sm 2+ . On the other hand, in the TiO 2 -containing glasses, electrons generated were preferably trapped in Ti 4+ ions so as to form ETC, resulting in no reduction of Sm 3+ ions. © 2005 Elsevier B.V. All rights reserved. Keywords: Sm; Reduction; Sol–gel glass; Fluorescence; ESR; Point defect 1. Introduction Rare-earth ions-doped glasses have widely been studied because of their unique optical properties and applications for opto-telecomunication, such as laser action, upconversion, amplifier and spectral hole burning [1,2]. Persistent spectral hole burning (PSHB) phenomena are especially interesting due to its application to frequency-domain optical data stor- age. Glasses are more preferred as a host matrix of rare-earth ions for their inhomogeneously broadened line width of opti- cal transitions, facile compositional variation and easy mass production. Recently, using a sol–gel technique, we prepared Sm 2+ ions-doped aluminosilicate glasses and demonstrated the PSHB up to room temperature [3–5]. Spectral holes are considered to be burnt by photoinduced chemical reactions within the rare-earth ions or between the rare-earth and matrix glass structure [6]. So far, we have investigated the reduction of Sm 3+ into Sm 2+ ions by X-ray or femtosecond laser irradiation and ∗ Corresponding author. Tel.: +81 52 735 5285; fax: +81 52 735 5285. E-mail address: nogami@nitech.ac.jp (M. Nogami). the formation of the PSHB. These glasses give faster and more efficient hole burning compared to the H 2 -gas treated glasses [3–5]. It was also noted that in the glasses irradi- ated with X-ray there were an amount of aluminium–oxygen hole centers (Al–OHC), which were hole centers trapped with oxygen bounded to the Al ions, and the generated quantity were closely correlated with the quantity of Sm 3+ reduction [7]. In this study, a X-ray reduction process of Sm 3+ ions in TiO 2 (ZrO 2 )–Al 2 O 3 –SiO 2 glasses was investigated in rela- tion with various point defects generated in each of these glasses. 2. Experiments 2.1. Sample preparation xTiO 2 (or ZrO 2 )–(10 - x)Al 2 O 3 –90SiO 2 (mol%) glasses doped with 10 wt% Sm 2 O 3 were prepared by the sol–gel pro- cess of Si(OC 2 H 5 ) 4 , Al(OC 4 H 9 ) 3 , Ti(OC 3 H 7 ) 4 , Zr(OC 3 H 7 ) 4 0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2004.11.084