Blue Luminescent Biogenic Silicon-Germanium Oxide Nanocomposites
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Blue Luminescent Biogenic Silicon-Germanium Oxide Nanocomposites Shuhong Liu1, Clayton Jeffryes1, Gregory L. Rorrer1, Chih-hung Chang1 Jun Jiao2 and Timothy Gutu2 1 Department of Chemical Engineering Department, Oregon State University, Corvallis, Oregon; 2 Department of Physics, Portland State University, Portland, Oregon. ABSTRACT Marine diatoms are a class of microalgae that possess cell walls composed of silica nanoparticles. These organisms actively assimilate silicic acid Si(OH)4 from seawater, polymerize silicic acid to silica nanoparticles by a protein-mediated precipitation process, then assemble the silica nanoparticles into intricate patterns that constitute the cell wall microarchitecture of the diatom frustule. The biomineralization capacity of marine diatoms, Nitzschia frustulum,was harnessed to biologically manufacture silicon oxide / germanium oxide nanocomposite materials. Germanium was incorporated into living diatom cell mass by a twostage cultivation process. The micro- and nanostructures of biogenic oxide nanocomposite were characterized by TEM with EDS, and XRD. Furthermore, photoluminescence (PL) measurements were performed on these biogenic nanocomposites with different post processing to study their optoelectronic properties. Strong blue photoluminescence was observed from samples treated with H2O2 and oxygen plasma. A clear blueshift was observed from the biogenic oxides with the addition of germanium. It is believed that self-trapped exciton affected by quantum confinement effect is responsible for the PL from these biogenic oxide nanocomposites. INTRODUCTION Diatoms are unicellular primitive algae that live abundantly in aqueous habitats. They have a unique ability to uptake soluble silicon from their surrounding environment and convert them into nanospheres of silica with uniform size distribution [1]. They have fascinated biologists for a long time, and recently they got more and more attention from nanotechnologists because of their spectacular capability to fabricate amorphous silica ordered at the nano and microscale [2]. Diatoms can produce nano-silica particles continuously via exponential growth of their cell walls. In particular, they can self assemble three-dimensional structures using the silica nanospheres as building blocks similar to bricks in a wall. Nanostructured silicon-germanium composite materials exhibit novel optoelectronic properties which can be used for photodetector and photovoltaic applications [3]. Since germanium is also a group IV element, diatoms might convert germanium to be nanostructured germanium oxide following a similar mechanism for the formation of nano-silica. In this study, the biomineralization capacity of marine diatoms, Nitzschia frustulum, was harnessed to biologically manufacture silicon oxide/germanium oxide nanocomposite materials. Germanium was incorporated into living diatom cell mass by a two-stage cultivation process. The micro- and nanostructures of biogenic oxide nanocomposite were characterized by SEM, TEM with EDS, and XRD. I
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