Influence of Halides on the Luminescence of Oxide/Anthracene/Polymer Nanocomposites
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Influence of Halides on the Luminescence of Oxide/Anthracene/Polymer Nanocomposites Dorothée V. Szabó, Heike Reuter, Sabine Schlabach, Christoph Lellig, Dieter Vollath1 Forschungszentrum Karlsruhe GmbH, Institute for Materials Research III, D- 76021 Karlsruhe 1 NanoConsulting, D-76297 Stutensee ABSTRACT Nanocomposites made of an oxide core of a wide band gap insulator, a lumophore monolayer of anthracene and an outer protecting layer of PMMA are studied regarding their luminescence properties and the influence of halides stemming either from the precursor used for synthesis or from the lumophore itself. Halide-free nanocomposites exhibit luminescence spectra resembling to that of anthracene with some significant differences concerning the intensity ratio and an additional peak at 420 nm. Nanocomposites made from chlorides show excimer-like spectra with broad maxima. In microanalysis residual chlorine can be detected. Chlorine-free oxide kernels, coated with 9,10 dichloroanthracene exhibit luminescence spectra resembling to a superposition of the pure lumophores 9 chloro- and 9,10 dichloroanthracene. It can be shown that the origin of the halide strongly influences, but does not quench the luminescence spectra of the powders. Suspensions of the chlorine containing nanocomposites in ethanol exhibit modified anthracene like spectra. This is a strong indication for dechlorination by proton-transfer in ethanol. Suspensions of the same material in water lead to spectra showing a superposition of excimer spectrum and modified anthracene spectrum. Here a partial dechlorination occurs. INTRODUCTION Luminescence in oxide/mPMMA nanocomposites [1,2], surface modified oxides [3] and polymer-dielectric nanocomposites [4] is a well-described phenomenon. As in oxide/mPMMA nanocomposites the luminescence emerges from the bonding between mPMMA and oxide, containing carbonyl groups responsible for luminescence [5], the variability in emission wavelength is very limited. Therefore, a completely new concept of nanoparticles for luminescence applications was developed: three-layered nanocomposites [6,7]. These particles consist of an oxide kernel, a monolayer of an organic lumophore, and a polymer layer for protection outside. Such multilayer nanocomposites are synthesized by a gas phase process, the Karlsruhe Microwave Plasma Process [8]. This process is characterized by low reaction temperatures, resulting in narrow particle size distribution of the nanoparticles and the possibility of in-situ coating of particles. Usually water-free chlorides, carbonyls, or metal-organics are well suited precursors for the synthesis of ceramic nanoparticles. As lumophores commercially available materials such as anthracene, pyrene, or perylene can be used. The protecting polymer coating generally is made from MMA (methyl methacrylic acid) which polymerizes under the UV radiation of the plasma. Due to interactions between ceramic kernel, lumophore interlayer and polymer coating, these materials exhibit luminescence properties, differing from
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