Compositional dependence of infrared absorption of iron-doped silicate glasses Koichi Sakaguchi a,b, * , Takashi Uchino c a Technical Research Laboratory, Nippon Sheet Glass Co., Ltd., 2-13-12, Konoike, Itami, Hyogo 664-8520, Japan b Department of Chemistry, Graduate School of Science and Technology, Kobe University, 1-1, Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan c Department of Chemistry, Faculty of Science, Kobe University, 1-1, Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan Received 29 December 2006 Available online 20 August 2007 Abstract Peak positions of infrared absorption of Fe 2+ were investigated for alkali alkaline-earth silicate and (alkali) alkaline-earth (alumino-)- silicate glasses. The obtained data for absorption-peak wavenumber m p were analyzed as a function of calculated optical basicity K c . For alkali alkaline-earth silicate glasses, increase of K c by substitution of SiO 2 for R 0 O increased m p , whereas increasing K c by substituting Mg 2+ for a larger alkaline-earth ion yielded the opposite trend. We consider that the composition changes vary effective negative charge on oxygen atoms and symmetry of their coordination around the Fe 2+ ion. For (alkali) alkaline-earth (alumino-)silicate glasses, m p depended on the Na 2 O/Al 2 O 3 ratio. ESR signals at g = 2.0 suggested clustering of Fe 3+ and possibly Fe 2+ ions in alkali-containing glasses and no clustering in alkali-free glasses. We consider that the negative charge of AlO À 4 is compensated preferentially by Fe 3+ and Fe 2+ ions when alkali cations are not present in glasses. Steep decrease of m p with increasing K c by substituting Mg 2+ for Ca 2+ was observed in the regions with a very low or no MgO content for all series of glasses containing alkali ions. The effect was probably due to direct interaction between the Fe 2+ ion and the Mg 2+ ion. Ó 2007 Elsevier B.V. All rights reserved. PACS: 42.70.Ce; 61.43.Fs; 78.20.Ci; 78.40.Pg Keywords: Absorption; Optical spectroscopy; Aluminosilicates; Soda-lime-silica 1. Introduction Many commercial glass products contain iron either as dopant or impurity. For example, iron-doped glasses are widely used for infrared-absorbing automotive windows which shield heat flux of sunshine. It is mainly the effect of the Fe 2+ ion, which exhibits a broad absorption band at around 10 000 cm À1 . The absorption usually gives blue coloration to the glass. Some other applications require colorless glasses. In these cases, iron ions, especially the Fe 2+ ion, should be decreased to yield high transmission in the visible range. Motivated partly by these practical needs, properties and structures of iron-containing glasses have been extensively investigated [1–14]. The peak position (wavenumber) of the infrared absorp- tion band (m p ) at around 10 000 cm À1 varies with glass com- position. Vogel [15] states that in iron-doped phosphate glasses for infrared filters in movie projector lamps, the Fe–O interaction is weakened by high field strength of P 5+ . The loosening of FeO 6 shifts m p to a lower wavenum- ber, and thus high transmission of near infrared region is obtained. Fox et al. [2] investigated compositional depen- dence of m p for xNa 2 O Æ ySiO 2 glasses and showed that m p increased with Na 2 O content of the glass. They claimed from the results that effective negative charge of oxygen 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.06.058 * Corresponding author. Address: Technical Research Laboratory, Nippon Sheet Glass Co., Ltd., 2-13-12, Konoike, Itami, Hyogo 664- 8520, Japan. Tel.: +81 72 781 0081; fax: +81 72 779 6906. E-mail address: KoichiSakaguchi@mail.nsg.co.jp (K. Sakaguchi). www.elsevier.com/locate/jnoncrysol Available online at www.sciencedirect.com Journal of Non-Crystalline Solids 353 (2007) 4753–4761