Light emission from crystalline silicon and amorphous silicon oxide (SiOx) nanoparticles

Bright orange-red light emission was observed from single crystal silicon nanoparticles and silicon oxide (SiO_x) nanoparticles. The emission peak was recorded at about 1.5 eV both at room temperature and 77K. Varying the mean silicon particle size, we observed no effect of particle diameter on the emission wavelength. Amorphous silicon oxide (SiO_x) nanoparticles also showed essentially the same emission spectrum as the crystalline particles. The absence of change in the photoluminescence (PL) spectrum with variations in particle size and crystallinity indicates that quantum confinement is not the controlling PL mechanism. An examination of the hydrogen content with relation to the PL intensity showed no direct correlation; however, all samples did contain some hydrogen, so its effect on PL cannot be ruled out. To test for the presence of photoluminescent siloxene on the surface of the particles, nitric acid was applied; a violent reaction occurred with the silicon particles, while the SiO_x particles showed no reaction. Taken in conjunction with the emission data, these experiments demonstrate that the PL of the SiO_x is also not dependant on siloxene. Evidence points to an amorphous coating as the source of photoluminescence.