PbS Quantum Dots in a Porous Matrix: Optical Characterization

We propose simple and practical method for creation of quantum dot (QD) systems in a porous matrix. The commercial filter paper is soaked in the colloidal solution of PbS QDs in carbon tetrachloride followed by drying. The samples prepared by the method demonstrate linear dependencies of optical density and photoluminescence intensity on the QD concentration, excellent homogeneity, and reproducibility. A red-shift of QD photoluminescence spectrum after their infiltration into the matrix and energy transfer between QDs of different sizes indicate formation of the close-packed QD system. Optical properties and stability of the close-packed PbS quantum dot systems are investigated at room temperature in a wide range of QD sizes. A strong reduction of average QD photoluminescence lifetime from 435 to 55 ns with decreasing QD diameter from 3.0 to 7.4 nm has been found. A blue-shift of the photoluminescence spectra accompanied by increasing the photoluminescence lifetime observed for small and medium QDs with the sample storage indicates decreasing the QD size due to oxidation of their surface.