Local growth of PbS NP in a xerogel impregnated with PbS precursors. The doping solution had a concentration of 0.37 M in lead acetate. (a) Photograph of a sample fs irradiated at 10 mW and TEM image of NPs obtained after fs irradiation at 40 mW. (b) TEM and HRTEM images after CW irradiation at 140 mW. (c) Average particle size against the laser power in both regimes. The power threshold has been measured for the CW laser. Dotted lines are extrapolations. (a and b) adapted from  and , respectively.