Effects of the sol-gel solution host on the chemical and optical properties of PbS quantum dots

PbS nanoparticles were prepared via a colloidal route using an organic capping agent, and were incorporated in both a silica and a titania sol-gel solution with a concentration of 10 mol%. The stability of the particles embedded in the sols was lengthened from 2 h to several days and their growth was considerably slowed down. The kinetics of the optical absorption allowed us to quantify the growth rate of the particles. Analysis of the optical emission in the three solutions (colloid, SiO2/PbS and TiO2/PbS) showed that the PbS nanocrystals are partially passivated by the silica chains and completely by the titania chains in the sols. Conjoint study of the optical absorption and emission measurements revealed a correlation between the presence of a structured exciton peak in the absorption spectra and the absence of shallow surface states.