November 2001 Ž . Materials Letters 51 2001 208–212 www.elsevier.comrlocatermatlet Structural changes induced by the catalyst in hybrid sol–gel films: a micro-Raman investigation D. Bersani a, ) , P.P. Lottici a , M. Casalboni b , P. Prosposito b a ( ) Istituto Nazionale per la Fisica della Materia INFM and Dipartimento di Fisica, UniÕersita di Parma, Parco Area delle Scienze 7a, ` 43100 Parma, Italy b ( ) Istituto Nazionale per la Fisica della Materia INFM and Dipartimento di Fisica, UniÕersita di Roma-Tor Vergata, ` V. della Ricerca Scientifica 1, Rome, Italy Received 4 September 2000; accepted 25 January 2001 Abstract The effect of acid catalysts on the structure and properties of zirconia-based hybrid organic–inorganic thin films obtained Ž . Ž . by sol–gel, starting from g-glycidoxypropyl-trimethoxysilane GLYMO and zirconium n-propoxide Zr C H , is studied 3 74 by means of micro-Raman spectroscopy. The kind of network formed during the polymerisation process depends on the catalyst: this modifies the reactivity of the organic moiety of the GLYMO and a glass former behaviour is obtained only when the epoxy ring of the GLYMO is cleaved. Unopened epoxy rings, on the other hand, may protect the guest luminescent molecules, like the azo-dyes, to acid attacks. Nitric and acetic acids are reported as examples. q 2001 Elsevier Science B.V. All rights reserved. PACS: 81.20.Fw; 78.30.Jw; 82.35.qt Keywords: Sol–gel technique; Organically modified silanes; GLYMO; Thin films; Micro-Raman; Polymerization 1. Introduction Ž . ORMOSILS organically modified silicates and Ž . ORMOCERS organically modified ceramics are interesting materials offering a wide spectrum of w x applications, from integrated optics 1,2 to the out- wx door artworks conservation 3 . These materials are silica-based organic–inor- wx ganic hybrid polymers 4 formed by an inorganic network, obtained by the hydrolysis and condensa- tion of alkoxy compounds, linking organic groups, ) Corresponding author. Tel.: q 39-521-905278; fax: q 39-521- 905223;. Ž . E-mail address: bersani@fis.unipr.it D. Bersani . with suitable chemical properties and acting as glass wx modifiers or as glass formers 5 . The degree of linking and cross-linking of the organic and inor- ganic networks influences the mechanical and chem- wx ical properties 6 , and can be controlled by varying, for example, the catalyst used in the sol–gel process wx 7 . The addition of zirconia to the silica-based films wx increases their refractive index 6 , while the inser- tion of different active molecules, in our case a Ž . typical azo dye as the Disperse Red 1 DR1 , easily allows one to obtain photoluminescent integrated w x devices 1,8–10 . Here we report on the hybrid materials obtained Ž . by glycidoxypropil-trimethoxysilane GLYMO and zirconium n-propoxide as precursors. The molecular 00167-577Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0167-577X 01 00291-9