Mechanism of Fluorescent Silicon Nanoparticles

摘要

Silicon (Si) is known to have an indirect bandgap transition, which means it has poor fluorescence properties. However, when engineered into sub-nm sized particles, Si nanoparticles become emissive due to quantum confinement. However, in unmodified Si particles, this effect is limited to generating red or near-infrared emission with low quantum yield. To resolve these limitations, surface-modification methods have successfully generated Si particles that emit in the blue, cyan, and green with quantum yields up to ~90%. These modifications have also made the Si nanoparticles water-soluble, making them promising in biological applications. To date, the mechanism of emission in these species is still unclear although it has been speculated that charge transfer of Si-O-N could be responsible. To investigate whether emission by these Si nanoparticles proceeds via a charge transfer mechanism, Stark spectroscopy is used. In this method, an external electric field is applied to the Si nanoparticles. Changes in the absorption and/or emission spectra due to the applied field can be taken as strong evidence for a charge transfer mechanism. From the results of Stark spectroscopy, Si nanoparticles are revealed to have ligand to metal charge transfer mechanism along with electric-field quenching, which is useful information for utilization into applications. Addition to the information found, a method of how to tune the emission maxima based on selection of ligands is prosed.