Synthesis & Characterization of Optically-Active Lanthanide-Doped Hybrid Inorganic-Organic Systems
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ABSTRACT The materials chemistry of sol-gel-derived inorganic-organic molecular composites offers significant potential for molecular-level systems design. One focus in this arena is the chemical design and microstructural engineering of optically-active systems. We report the generation of rare-earth-doped inorganic-organic hybrids, based on a bridged polysilsesquioxane architecture. Derived from lanthanide precursors such as Erbium isopropoxide, which we co-condense with the requisite silsesquioxane monomer, these systems exhibit significant optical activity. In experiments on hybrids doped with Erbium, we conclusively demonstrate strong fluorescence at wavelengths in the vicinity of 1540 nm, from stimulation with 488 nm radiation. We discuss materials-driven impacts of the bridged-silsesquioxane architecture on system complexities arising from the solution sol-gel route which would affect fluorescence efficiencies and luminescence levels, such as hydroxyl impurities and clustering-effects. INTRODUCTION Hybrid inorganic-organic molecular composite systems derived through sol-gel processing are multicomponent materials that can potentially be designed for a wide range of applications[I]. System structural diversity can be achieved via modification and control of the relative ratio of inorganic/organic content, the degree of inorganic/organic interpenetration, the chemical nature of each component, reaction conditions utilized for synthesis, and the specific microarchitecture generated[2]. Bridged polysilsesquioxanes are an emerging subset of this class of materials which are distinguished by direct chemical incorporation of the organic component within the inorganic framework as a "bridging" construct[3]; the materials architecture of these systems permits the molecular design and engineering of a broad range of structures with potential for both passive as well as active applications. We are probing such systems incorporating specific inclusions within a "Guest-Host" motif for generation of sol-gel-derived glassy materials with engineered photonic or optoelectronic functionality. In this report, we discuss the synthesis and characterization of bridged polysilsesquioxanes doped with trivalent lanthanide ions with a focus on photophysical properties of erbium-doped systems, as schematized in Figure 1(i). Lanthanide-doped systems are of interest for various current and potential applications[4]. For erbium systems, the 411312 -- 44Is5/2 electronic transition results in photoluminescence in the vicinity of 1540 nm, a spectral region corresponding to the wavelength of minimum signal attenuation in low-loss silica-based optical fiber. While sol-gel chemistry provides an alternative low-temperature preparative route to typical approaches for erbium-ion-doped glassy systems, the associated drawbacks inherent to 433 Mat. Res. Soc. Symp. Proc. Vol. 576 © 1999 Materials Research Society
the chemistry are well known [5-6]. In particular, the optical response of such systems is typically impaired due to residual -OH from in
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