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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.

X-ray structural analysis, together with steady-state and transient optical spectroscopy, is used for studying the morphology and optical properties of quantum dot superlattices (QDSLs) formed on glass substrates by the self-organization of PbS quantum dots with a variety of surface ligands. The diameter of the PbS QDs varies from 2.8 to 8.9 nm. The QDSL's period is proportional to the dot diameter, increasing slightly with dot size due to the increase in ligand layer thickness. Removal of the ligands has a number of effects on the morphology of QDSLs formed from the dots of different sizes: for small QDs the reduction in the amount of ligands obstructs the self-organization process, impairing the ordering of the QDSLs, while for large QDs the ordering of the superlattice structure is improved, with an interdot distance as low as 0.4 nm allowing rapid charge carrier transport through the QDSLs. QDSL formation does not induce significant changes to the absorption and photoluminescence spectra of the QDs. However, the luminescence decay time is reduced dramatically, due to the appearance of nonradiative relaxation channels.

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