Optical Properties of Polymer-Embedded Silicon Nanoparticles
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Optical Properties of Polymer-Embedded Silicon Nanoparticles William D. Kirkey1, Alexander N. Cartwright1, Xuegeng Li2, Yuanqing He2, Mark T. Swihart2, Yudhisthira Sahoo3, and Paras N. Prasad3 Departments of 1Electrical Engineering, 2Chemical Engineering, and 3Chemistry and Institute for Lasers, Photonics, and Biophotonics State University of New York at Buffalo, U.S.A. 1 332 Bonner Hall, Buffalo, NY 14260, U.S.A. ABSTRACT We seek to use electrically conducting polymers, such as those commonly utilized in polymeric LEDs, as hosts for silicon nanoparticles. The proper design of multilayered devices based on these materials will yield efficient light-emitters in which charge carriers localize and recombine within the nanoparticles. Furthermore, these may combine the flexibility and processability of polymeric LEDs with the reliability of inorganic materials. We have synthesized luminescent silicon nanoparticles and have characterized their photoluminescence (PL) using continuous-wave and time-resolved spectroscopy. These particles have been incorporated into a variety of transparent solid hosts. The photoluminescence obtained from particle-containing poly(methyl methacrylate) (PMMA) matrices is very similar to that of the particles in solution, both in spectral content and PL decay characteristics. However, when incorporated into a variety of conducting polymers, such as poly(N-vinylcarbazole) (PVK), the nanoparticles do not retain their photoluminescence properties. A variety of chemical species have been reported as effective PL quenchers for porous silicon. We believe that these polymers quench the luminescence through similar mechanisms. Protective passivation of the nanoparticle surface is suggested as a strategy for overcoming this quenching. INTRODUCTION Nanocrystalline silicon has received a great deal of attention in recent years as a material that might be easily integrated into silicon wafer processing and utilized for biological and chemical sensing or for light-emitting devices. The well-established effects of the surface termination and the surrounding environment on the silicon photoluminescence (PL) are advantageous for sensing applications, but present a problem for optoelectronic applications requiring stable light emission. One solution is to produce silicon nanoparticles within SiO2, for example by implanting Si ions into a glass substrate and thermally annealing the composite. These materials show promise for use as optical devices; optical gain has been reported in nanoparticles produced by this method[1]. An alternate approach is to produce colloidal nanoparticles that can then be incorporated into transparent hosts such as polymers or xerogels. Various researchers have incorporated luminescent nanoparticles within electrically conducting polymers to yield hybrid electroluminescent devices[2-5]. However, to our knowledge, no study of luminescence from silicon nanoparticles embedded in such materials has been reported. The work presented in this paper is focused on the application of su
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