Fabrication of Highly Stable, Hybrid PbS Nanocomposites in PAMAM Dendrimer Matrix for Photodetection

A novel dendrimer-templating one step method for the in situ synthesis of hybrid nanocomposites of lead sulfide (PbS) quantum dots (QDs) of average diameter of 2.5-4.5 nm in poly(amidoamine) dendrimer matrix (PAMAM) at ambient condition is reported here. The PbS QDs are developed in cubic crystallographic phase with a high degree of crystallinity. FTIR analysis confirm a direct evidence of PbS QDs linkage to the surface functional groups of dendrimer molecules, which provides a way to prevent the aggregation tendency of the PbS QDs retaining the original properties in 3D rigid dendrimer matrix. Additionally, the thermal stability of dendrimer molecule increases in the nanocomposite unit indicating strong interaction of inorganic phases with dendrimer. The as-prepared PbS nanocomposites could be stored for three months at 4 degrees C retaining original optical characteristics. The synthesis route provides a simplified colloidal route for producing monodisperse hybrid PbS nanocomposites with robust optical properties. Pure dendrimer is photo inactive, while upon white light irradiation, the PbS nanocomposites results in enhanced photocurrent compared to the dark measurement. Repetitive on-off device response upon white light illumination is found to be sharp and repeatable over successive on/off irradiation cycles. The photoresponse of PbS nanocomposites promises application in photoswitching and photosensitive detectors.