Role of optically active defects in photoluminescence properties of diatom frustules

Diatoms are a group of unicellular photosynthetic algae having intricately patterned silica cell walls called frustules, which are made of amorphous silica. These frustules exhibit strong visible photoluminescence (PL) property when exposed to radiation of suitable frequency. Although silanol could be one of the major sources of the observed PL for high energy irradiation (> 5 eV), its origin for low-energy excitation is still debatable. In this study, PL spectroscopy of the diatom frustules was carried out using low energy (< 4.2 eV) excitation and correlated with UV–vis and Fourier transform infrared spectroscopy to analyse the role of various optically active defects and impurity groups responsible for diatom frustules PL. Theoretical calculations based on density functional theory were also conducted to verify the experimental findings.