Spectral features of composite oil-in-water emulsions containing silicon nanoparticles

A complex spectroscopic investigation of oil-in-water emulsions containing silicon nanoparticles synthesized by plasma chemical vapor deposition has been performed for the first time. It is established by electron microscopy and Raman and IR spectroscopy that nanoparticles synthesized by this method have a crystalline structure, sizes of about 10–15 nm, and an outer shell whose chemical composition depends on the powder synthesis atmosphere. Comparative measurements of the transmission spectra of silicon-containing emulsions showed that their transmission, taking into account scattering, decreases with a decrease in wavelength in the range below 450 nm. The wavelength dependences for particles with an oxynitride outer shell and particles having an oxide shell are significantly different. This result indicates a contribution of the outer shell of silicon nanoparticles to the transmission spectra of emulsions. This factor must be taken into account in design of UV protectors based on silicon powder. In addition, calculations performed for transparent media containing silicon nanoparticles predict the possibility of enhancement of the protective properties of such emulsions in the UV range with increasing sizes of particles above 10 nm.