Photoluminescence properties investigation of germanium inserted biosilica generated by bioreactor culture of marine diatom Nitzschia frustulum Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/cf95jf36q

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  • The purpose of this research was to investigate the optoelectronic properties of the Ge doped biosilica, mainly focused on the photoluminescence (PL) properties of diatom frustules of N. frustulum that contain metabolically inserted germanium oxide produced by a two-stage photobioreactor cultivation process. In order to explain the observed PL intensity and peak change due to germanium incorporation, the effect of Ge insertion on growth of N. frustulum was studied first. It was found that Ge inhibited diatom growth and silicon uptake rate when the Ge to Si molar ratio was increased to 0.14 although this inhibition was not observed when the ratio was less than 0.07. Ge uptake rate was also decreased from 0.458 ± 0.018 mL/10⁷cells-hr to 0.183 ± 0.017 mL/10⁷cells-hr as initial soluble Ge concentration in the nutrients in stage II increased from 12 µM to 85 µM. This Ge uptake inhibition at high initial Ge concentration suggested that the amount of Ge incorporated in frustules will increase to a maximum value, which was found in our experiment as 1.20 ± 0.22 wt%Ge in biosilica at Ge concentration level of 30.4 µM. The effect of germanium insertion on PL emission of frustules of diatom N. frustulum was studied. The PL peak intensity of Ge inserted frustules was much lower compared to frustules without Ge (controls). As the level of Ge incorporated into the frustules increased, the PL peak intensity decreased. The peak wavelength of frustules was shifted from 524 nm to 457 nm when Ge was inserted. However, the wavelength shift was not very sensitive to the Ge concentration incorporated into the silica frustules. Finally, TEM images of the submicron morphology of diatom frustule with and without Ge incorporation were studied. It was found that the pore structure of diatom frustule was altered to a slit-like structure due to Ge incorporation. The possible origin of the observed PL emission due to Ge insertion was proposed. It was suggested that the PL peak intensity decrease and peak wavelength shift were caused by the pore structure alternation.
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