PbS-doped mesostructured silica films with high optical nonlinearity

Mesostructured silica films have been doped with lead sulfide (PbS) nanocrystals by a two-step impregnation, using the mesopores as nanoreactors for PbS growth. Secondary ion mass spectrometry and transmission electron microscopy characterizations demonstrated nanocrystals growth inside the pores and throughout the film thickness, pointing out the feasibility of an impregnation-based synthesis made possible by the porous properties of mesoporous silica films. The mean particles diameter is 5 nm, which is compatible with the pore dimensions. The mesostructure order was retained after the growth of the nanocrystals, as pointed out by small-angle X-ray scattering measurements. Optical absorption and Z-scan measurements indicated that PbS nanoparticles show a quantum confinement effect, while the films are characterized by high nonlinearities of the optical response. The optical properties of this material can be usefully exploited in several nonlinear optical applications.