Preparation, characterization, and micropatterning of laser-dye-doped sol-gel films
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G. Rizzo, S. Galvagno, and G. Neri Dipartimento di Chimica Industriale ed Ingegneria dei Materiali, Universita` di Messina, I-88166 Messina, Italy (Received 7 August 2001; accepted 29 May 2002)
Planar thin films of dye-doped silica were prepared by sol-gel synthesis. The optical properties of the films were characterized by transmittance measurements in the visible-infrared range and by photoluminescence. Micropatterns whose feature size was on the order of 2.4 m, were imprinted on the film surface by a simple soft lithography approach. An optical microscope interfaced to a charge-coupled device camera was used to image the imprinted patterns and to analyze the patterned films photoluminescence. A sensitive spectral narrowing of the emission, which occurred only in micropatterned films, was attributed to the lateral confinement of the luminescence due to the micrometer-scale modulation of refractive index produced by the embossing procedure. I. INTRODUCTION
II. EXPERIMENTAL
Over the past decade the sol-gel technique has been used extensively as a versatile tool for preparing easy processable dielectric materials to be used in photonic applications such as waveguides,1–3 sensors,4,5 and optical devices.6–8 Unlike other methods traditionally used to prepare silica, the sol-gel synthesis has the unique peculiarity of working at room temperature. Accordingly, solgel processing allows the preparation of inorganic networks doped with a variety of thermally unstable organic dopants including photochromic dyes, liquid crystals, and nonlinear optical chromophores. The ease with which doped sol-gel glasses can be prepared, in conjunction with their low optical loss and high temporal, chemical, and mechanical stability, guarantees the strategic role of these materials in the development of optical devices.9–12 Moreover, the combined use of sol-gel synthesis and materials processing techniques such as spin-coating and soft lithography,13,15 represents a promising approach to designing new generation micro- or nanostructured devices. As an example, micropatterned dye-doped silica has been used to develop sol-gel-derived mirrorless microlasers operating in the visible range.16 In this framework, we used a sol-gel approach to prepare hybrid organic–inorganic films doped with a green-emitting laser-dye. The films were characterized by spectrophotometric measurements. In an attempt to laterally confine light in the silica films plane, micropatterns were imprinted on the films surface by hot embossing lithography. The light emitted from micrometer-scale patterned films was imaged and analyzed by an optical microscope interfaced with a charge-coupled device (CCD) camera.
The dye-doped silica samples were prepared from solutions obtained by mixing tetraethyl orthosilicate (TEOS), triethoxy-vinyl silane (TEVS), and water. All the precursors were purchased from Aldrich (Germany) and were used as received. The initial solutions were typically composed of 20 ml TEOS (or TEVS), and 6 ml 0.5 M hydrochloric acid, acting as a catalyst. B
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