Photoluminescent, transparent and flexible di-ureasil hybrids containing CdSe/ZnS quantum dots

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Abstract
We describe, in this paper, the sol-gel synthesis of di-ureasil based nanocomposites prepared in situ in the presence of organically capped CdSe quantum dots (QDs) or CdSe QDs which have been coated with a ZnS shell. For the latter a new chemical route to coat the CdSe QDs with ZnS shells was investigated and is now reported. The QDs became well dispersed in the final nanocomposites, whose microstructural homogeneity was evaluated by atomic force microscopy (AFM) and transmission electron microscopy (TEM) analyses. In order to understand the optical behaviour of di-ureasil containing QDs, a detailed photoluminescent study was undertaken for a selected particle size distribution of ZnS coated CdSe QDs (d∼4.5 nm). Emission quantum yields up to 0.11 were measured in the final nanocomposites that present a huge (between 3 and 6 orders of magnitude) increase in the lifetime of the QDs (relative to that of isolated ones), as a result of energy transfer occurring between the intimately mixed di-ureasil host and the QDs.