The Effect of Temperature on the Photoluminescence of Hybrid Si/SiOx Nanoparticles

Abstract

Transformation of the photoluminescence (PL) spectra of hybrid Si/SiO_x nanoparticles of the crystalline core–oxide shell type has been investigated in the temperature range of 10–320 K upon 325-nm laser excitation. Si/SiO_x nanoparticles are synthesized from silicon monoxide and functionalized in dimethyl sulfoxide (DMSO) or octadecene (OD). The PL spectra of the nanoparticles are considered as superpositions of short-wavelength (400–550 nm) and long-wavelength (600–900 nm) bands, which have significantly different ratios of the total intensities of these components in Si/SiO_x/OD and Si/SiO_x/DMSO samples. For Si/SiO_x/DMSO samples, the intensity of the short-wavelength band monotonically decreases with an increase in temperature from 10 K, whereas the intensity of the long-wavelength band first increases; however, then (at approximately 70 K) its slope begins to decrease and levels off. The specific features of the temperature dependence of the long-wavelength PL band intensity can be explained in this case by efficient energy transfer from defect oxygen-containing centers at the core boundary to exciton centers that arise under laser irradiation. In the case of Si/SiO_x/OD particles, for which the short-wavelength band intensity is initially low, this effect is not observed. For these particles, the influence of 405-nm cw laser radiation on the kinetics of changes in the intensity of the long-wavelength PL band has been studied beginning with a temperature of 10 K. It has been found that the PL intensity increases at temperatures near 10 K with an increase in the exposure time, which is explained by additional heating of nanoparticles in a vacuum.