Materials Science and Engineering B 165 (2009) 252–255 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Photoluminescence properties of porous silicon/fluorene dye composites M. Fakis a,∗ , F. Zacharatos b , V. Gianneta b , P. Persephonis a , V. Giannetas a , A.G. Nassiopoulou b a Department of Physics, University of Patras, 26504 Patras, Greece b IMEL/NCSR Demokritos, Aghia Paraskevi, 153 10 Athens, Greece article info Article history: Received 31 August 2008 Received in revised form 25 March 2009 Accepted 4 June 2009 Keywords: Porous silicon Photoluminescence properties Fluorene dye Hybrid materials abstract We report on the fabrication and the photoluminescence (PL) study of hybrid nanocomposites formed by embedding fluorene dye molecules in the vertical cylindrical nanopores of a nanoporous silicon layer. The pores had a diameter of ∼20 nm and were homogeneously filled with the fluorene molecules as evidenced by scanning electron microscopy images. Efficient PL in the blue spectral region, attributed to the fluorene dyes embedded into the pores, was obtained from the composites. The PL spectrum of the dyes in porous silicon is blue-shifted compared to their PL spectrum in solution due to the confinement and isolation of the molecules into the pores. This blue-shift was enhanced when the dyes were initially dissolved in an aromatic solvent. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Hybrid composites fabricated by organic dyes and inorganic materials have received a great amount of interest due to their potential use in lasers and light emitting diodes [1–3]. The hybrids can have the advantages of both systems, namely flexibility, light weight and enhanced light emitting properties from the organic dyes as well as thermal, chemical and mechanical stability from the inorganic part. Porous silicon (PS) has been used as a template for embedding organic molecules and polymers [4–9]. Generally, this leads to the isolation of the active organic molecules into the pores, suppressing intermolecular as well as solvent–solute interactions. Additionally, the organic molecules are protected from the envi- ronment leading to an increase of the material’s lifetime. The use of PS as the inorganic matrix for embedding the organic material is very interesting, essentially towards integration of the potential devices with Si electronics. PS can be fabricated locally on the Si substrate by electrochemistry and the well established Si process- ing techniques can be used for device fabrication. The structure of PS depends strongly on the resistivity of the substrate and the electrochemical conditions used for its preparation. We can dis- tinguish between mesoporous Si with randomly distributed pores [10] and macroporous [11–14] or nanoporous Si [12,15], with verti- cal cylindrical pores in the micron or nanoscale, respectively. In this work, the PS material used was mesoporous with ∼20 nm-diameter vertical cylindrical pores, grown on a p + -type Si substrate. In this material, although it contained nanopores, the remaining Si walls ∗ Corresponding author. E-mail address: fakis@upatras.gr (M. Fakis). were thick. As a consequence, it did not show any luminescence at room temperature, as in the case of highly mesoporous Si grown on a p-type wafer [10], but it kept the properties of bulk Si that does not emit any visible light at room temperature. It thus constituted a perfect matrix for the present study, since the observed PL from the organic material did not interfere with any luminescence from the matrix. Concerning the organic materials, a great amount of photonic polymers and oligomers have been studied during the last 15 years. Among this great amount of organic compounds, the fluorenes have received an increased scientific interest due to their enhanced chemical purity and stability as well as their increased structural order and planarity. Additionally, the fluorenes generally exhibit high PL efficiency and good non-linear optical properties [16,17]. Fluorene is a planar group containing two benzene rings linked with a five-member ring providing high overlap of -orbitals. For the penetration of the organic molecules inside the pores of PS there are several factors playing an important role. These are the type of the molecule, its molecular volume as well as the solvent used to dissolve the molecules [7,18,19]. In this paper, we report on the PL study of hybrid nanocompos- ites made by embedding fluorene dyes into the vertical cylindrical nanopores of a mesoporous Si material. The fluorene dyes consist of a fluorene central core and phthalimide edge substituents. The role of the solvent used to dissolve the fluorenes on the PL properties of the composites is examined. 2. Experimental The starting material in this investigation was a heavily doped p-type (1 0 0) Si wafer with a resistivity of 5 m cm. The surface of 0921-5107/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2009.06.001