Morais Faustino, Bruno Miguel (2016) Preparation and luminescent properties of nanoparticle-organic polymer composites. (PhD thesis), Kingston University, .
Abstract
This thesis reports investigations into some photophysical aspects of luminescent nanocomposites in a number of different systems. The preparation of Ln[sup]3+ doped rutile SnO[sub]2 (Ln = Sm, Eu, Tb, Ho, Nd) by a sol-gel method is described. Average particle size was found to be 23nm by x-ray powder diffraction and electron microscopy. Factors affecting growth kinetics are also discussed. Successful sensitisation of Ln[sup]3+ emission via SnO[sub]2 host energy transfer is reported. Optimum Ln[su]3+ concentrations were investigated and a proposed mechanism of Dexter type energy transfer based on SnO[sub]2 lattice defects acting as sensitising centres is presented. The relationship between the Ln ionic radius and the dopant concentration required to maximise its emission is also explored. It was found that the larger the ionic radii, the less Ln[sup]3+ was required to maximise its emission. Investigations into the distance dependence of the energy transfer between Ln[su]3+ and Sn[sup]4+ as well as between neighbouring Ln[su]3+ ions have been undertaken - e.g. it was concluded that maximum Sm[sup]3+ sensitisation occurred when every fourth Sn ion was substituted by Sm. Poly(p-phenylene vinylene) (PPV) was synthesised via the thermal conversion route proposed by Wessling and Zimmerman. Monomers, precursor polymer and polymer were fully characterized by means of infra-red, UV-Vis absorption and photoluminescence spectroscopy. By-products were also characterised by [sup]1H and [sup]3C-NMR. Incorporation of the SnO2:Ln[sup]3+ nanocomposites into PPV was followed by extensive photoluminescent studies. It was found that sensitisation of both polymer and lanthanide was dependent on the system composition and concentration ratios. There was clear evidence to support successful harvesting of PPV non-emissive triplet state energy into useful Ln[sup]3+ photon emission. To better benefit from triplet state population, a poly(vinyl alcohol) (PVA) two-dimensional hydrogen-bonded cage was used to reduce the triplet quenching. A proposed mechanism of energy transfer is described for each system. Finally, poly(2,5-bis(3-sulfonatoproproxy)-1,4-phenylene, disodium salt-alt-1,4-phenylene) (PPP-OPSO[sub]3) was used as a donor, to systematically compare the effect of SnO[sub]2:Ln[sup]3+ nanoparticles on the luminescence of a polymer with a larger band gap and higher triplet state energy. It was established that the high triplet state of PPP-OPSO[sub]3 matched the emissive levels of most lanthanides, and a clear indication of triplet harvesting by Eu[sup]3+ was obtained under oxygen-free conditions in a PVA amtrix. Exchange of the polymer's Na{sup]+ cation by Eu[sup]3+ brought both donor and acceptor into close proximity. Dexter type energy transfer was seen from both singlet and triplet states, with Eu[sup]3+ emission lifetimes as long as 400ms in phosphorescence measurements.
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