Effect of water and UV passivation on the luminescence of suspensions of silicon quantum dots

This article presents the evolution of the photo-luminescence (PL) of silicon quantum dots (QDs) with an average diameter of 5–6 nm dispersed in alcohol under different conditions. Two samples were considered after alcohol dispersion: freshly synthesized (kept in air for 2 days) QDs which do not exhibit luminescence and air-aged (kept in air for 2 years) QDs exhibiting red-IR luminescence. Experiments performed with addition of a small volume of water, followed by heating for different times showed that the oxidation occurs gradually until transforming totally the initial material in SiO₂. The oxidation process does not enable the appearance of PL from the Si core for dispersed non-aged powders, while it results in a blue shift of the PL maximum intensity for the aged ones. The results obtained after UV illumination clearly indicate an effect of the UV irradiation on the luminescence of QDs dispersed in aqueous environment, and the treatments with acidic water lead to the conclusion of a possible enhancement of the PL by hydrogen passivation of the non-radiative defects. This result should be taken into account for post-production treatments and applications, more particularly, considering a controlled and safe use of luminescent Si QDs.