Ordered fabrication of luminescent multilayered thin films of CdSe quantum dots

The surface of CdSe nanoparticles was functionalized with 11-hydroxyundecanoic acid (11-HUDA) during in situ preparation to afford stable and highly luminescent quantum dot (QD) solutions. The reactivity of the hydroxyl groups of 11-HUDA was then utilized in carbamate bond forming reactions with diisocyanate-bearing molecules that serve as linkers in the fabrication of the multilayered CdSe quantum dot films. The covalent bond formation readily proceeds at ambient temperature and results in a layer-by-layer formation of thin films comprised of photoluminescent CdSe nanoparticles separated by long chain organic connectors. The successive layer-by-layer approach can be repeated multiple times to get the desired thickness of QD films on glass or silicon substrates. The atomic force microscopy indicated the successful attachment of the QDs on the substrate surface. Importantly, the in situ functionalized CdSe nanoparticles preserve their stable and highly photoluminescent optical properties in the resulting multilayered films. Moreover, there is a gradual increase in the intensities of electronic absorption and photoluminescent bands of the QDs with increasing the number of layers, confirming successful fabrication of the multilayered films. The quantum yield (QY) of the 12-layered film was measured to be 6%. These findings are important for the development of QD-based optical, electronic and sensing devices that can harness the highly photoluminescent properties of these ordered and stable nanocomposite materials.