Rhodamine 6G impregnated porous silica: A photoluminescence study A. Anedda, C.M. Carbonaro * , F. Clemente, R. Corpino, P.C. Ricci, S. Rossini Dipartimento di Fisica, Universita ` degli Studi di Cagliari and INMF UdR Cagliari, SP n-8, Km 0,700, 09042, Monserrato (Ca), Italy Available online 18 July 2005 Abstract The optical properties of rhodamine 6G dye confined in porous silica are reported. Photoluminescence properties of embedded chromophores in mesoporous hosts can be affected by the surrounding matrices: shifts in emission spectra and variations of photoluminescence quantum yield are found as compared to dye solutions. Host – guest interactions are studied here by varying both SiO 2 xerogels porosity and the dye concentration. Comparing samples obtained by impregnating matrices with 5.4 and 18.2 nm pores with solutions having concentrations in the rhodamine 6G high laser gain, matrices with 5.4 nm pores impregnated with a dye concentration of 5  10  4 M are found to be the most stable and efficient in the examined range. D 2005 Elsevier B.V. All rights reserved. Keywords: Porous silica; Dye; Photoluminescence; Hybrids 1. Introduction Studies on the feasibility of solid-state dye laser have recently enjoyed increasing interest: the possibility to have rigid, compact, non-toxic media with high mechanical and thermal stability within which multiwavelength emitters are hosted can have several technological applications ranging from optics to remote sensing [1–5]. Moreover, dye molecules embedded in solid matrices have emerged as potential non-linear optical materials [1–5]. When develo- ping a solid-state dye laser, one of the most important problems to face is dye photostability which is mainly related to the photochemical degradation of organic molecules in their gain range [4,6–13]. In addition, host– guest compatibility and interactions play a major role when embedding dyes in a solid matrix. Different organic and inorganic hosts have been extensively studied with the aim of increasing mechanical, thermal and photochemical stability of embedded guests with specific functionality [4,6–13]. Within this scenario, sol –gel synthesized porous silica emerged as an ideal host to confine photoluminescent molecules: its range of optical transparency is compatible with the emission of several dye molecules in the visible and near ultraviolet range [14,15]. Moreover, its chemical, thermal and mechanical stability are particularly suitable to engineer stable photoluminescent devices [1 – 5,14,15]. Sol–gel chemistry allows tailoring both thin films and monoliths with controlled porosity, shaping and patterning of pure or doped SiO 2 matrices and functional hybrids [1,5,14,15]. Different methods to trap organic molecules within solid substrates have been developed, including direct soaking of the host with dye solutions (type I) and the synthesis of organic – inorganic hybrids through the sol – gel process (type I and II) [1,16,17]. In type I samples, the chemical bond between organic molecules and inorganic matrices is weak (hydrogen bonding, Van der Waals interactions, phisisorption etc). This class of hybrids can be obtained through impregnation of solid hosts with solutions of the desired molecule or by adding dopants at the sol stage of a sol–gel synthesis. Type II samples are characterized by a covalent bond between host and guest and are obtained via sol–gel [16,17]. This study is a part of a project devoted to the characteri- zation and understanding of functional hybrid nanocompo- 0928-4931/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2005.06.033 * Corresponding author. Tel.: +39 0706754755; fax: +39 070510171. E-mail address: cm.carbonaro@dsf.unica.it (C.M. Carbonaro). Materials Science and Engineering C 25 (2005) 641 – 644 www.elsevier.com/locate/msec