Luminescence Studies of Nanoporous Germanium Doped Biosilica in Fresh Water Diatoms

Diatoms are single-celled photosynthetic algae of the class Bacillariophyceae. Diatom samples were collected from Deepor beel (a Ramsar site) on the basis of habitat stratification. The diatom frustules were treated by acid to remove the organic matrix remain external to cell wall. X-ray diffraction (XRD) studies were carried out to visualize the structural properties of the frustules and ultra-violet-visible spectroscopy was done to study the optical properties of the silica frustules. Photoluminescence properties of diatom frustules at various excitation wavelengths were done. The natural diatom frustules were excited at 250 nm, 285 nm and 329 nm, whereas, the Ge doped diatoms were excited at 280 nm, 370 nm and 412 nm respectively.  The PL spectra for natural diatom frustules showed a diverse range of PL peaks at ultraviolet, blue and green ranges which, confirmed that the diatoms used in this study were more potential with optoelectronic behaviours. For TRPL analysis, the natural as well as Ge doped diatom frustules were excited at 375 nm, demonstrated the decay time in the range between 3.85 eV to 2.67 eV for natural diatoms and 2.94 eV to 2.38 eV for Ge doped diatoms. It was found after fitting the parameters that the decay best fitted for biexponential decay in case of natural diatoms and tetra exponential in case of Ge doped diatoms.

Keywords: Diatom frustule, photoluminescence, nanoporous silica, Ge doped biosilica