Influence of solvent electron affinity on paramagnetic defects in hybrid Si/SiOx luminescent nanoparticles

Luminescence of 1-octadecene-coated silicon nanoparticles with 8 nm crystalline core in hexane and CCl4 colloidal solutions and its reversible photobleaching were examined. In agreement with previous reports, anti-correlation of luminescence intensity and the number of paramagnetic defects were found in hexane. Luminescence intensity is decreased by 75% during 30 min of 405 nm laser irradiation while the number of paramagnetic defects is increased by 65%. Paramagnetic defects were supposed to be silicon dangling bonds. In CCl4 colloidal solution, this correlation is lost: photobleaching is similar to hexane colloidal solution, while the number of paramagnetic defects is not changed during irradiation. Electron trapping and subsequent breaking of weak Si-Si bonds are proposed to be the reason of formation of silicon dangling bonds during irradiation. DFT calculation of geometry and g-tensor of Si-vacancy on the boundary of crystalline silicon core and oxide shell was performed. Formation of paramagnetic defects is supposed to be a by-process responsible only for a minor effect on luminescence intensity.