While silicon nanocrystals embedded in silicon dioxide thin films have been intensively studied in physics, the potential of batch synthesis of silicon nanocrystals from the solid-state disproportionation of SiO powder has not drawn much attention in chemistry. Herein we describe some remarkable effects observed in the diffraction, microscopy and spectroscopy of SiO powder upon heat treatment in the temperature range 850-1100 ℃. Quantum and spatial confinement effects related to the size of the silicon nanocrystals nucleated and grown in this way were established by PXRD, STEM, Raman, FTIR and UV-Visible spectroscopy. With this know-how a high yield synthesis was developed that produced polydispersions of decyl-capped, hexane-soluble silicon nanocrystals exclusively with near infrared (NIR) photoluminescence (PL). Using size-selective crystallization, these silicon nanocrystals were separated into monodisperse fractions, which allowed their photoluminescent absolute quantum yield (PL AQY) to be studied as a function of silicon nanocrystal size. This investigation yielded a plot showing the three regions of which, from longest to shortest PL wavelength, define the (i) transition from bulk non-emissive silicon to quantum confined emissive silicon, (ii) increasing spatial confinement of electron-hole pairs enhancing radiative recombination, and (iii) increasing contributions of organic-capping group vibrations and surface defects favouring non-radiative recombination.

Silicon monoxide: A convenient precursor for near infrared emitting silicon nanocrystals and switching-on quantum size effects

249th National Meeting (2015)

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