Morphology-Dependent Energy Transfer of Polyfluorene Nanoparticles Decorating InGaN/GaN Quantum-Well Nanopillars

Conjugated polymer nanoparticles (CPNs), prepared in aqueous dispersion from poly[(9,9-bis{3bromopropyl}fluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1,3}-thiodiazole)] (PFBT-Br), are incorporated into a nanopillar architecture of InGaN/GaN multiple quantum wells (MQWs) to demonstrate a new organic/inorganic class of nanostructured excitonic model system. This hybrid system enables intimate integration for strong exciton−exciton interactions through nonradiative energy transfer (NRET) between the integrated CPNs and MQW pillars. The NRET of these excitonic systems is systematically investigated at varied temperatures. In these hybrids, InGaN/GaN MQWs serve as the donor of the NRET pair, while immobilized PFBT-Br polymer serves as the acceptor. To understand morphology-dependent NRET, PFBT-Br CPNs coating InGaN/GaN MQWs are made to defold into polymer chains by in situ treatment with a good solvent (THF). The experimental results indicate that NRET is significantly stronger in the case of CPNs compared with their defolded polymer chains. At room temperature, while the NRET efficiency of open polymer chains−nanopillar system is only 10%, PFBT-Br CPNs exhibit a substantially higher NRET efficiency of 33% (preserving the total number of polymer molecules). The NRET efficiency of the nanoparticle systems is observed to be 25% at 250 K, 22% at 200 K, 19% at 150 K, and 15% at 100 K. On the other hand, the defolded polymer chains exhibit significantly lower NRET efficiencies of 17% at 250 K, 16% at 200 K, 11% at 150 K, and 5% at 100 K. This work may potentially open up new opportunities for the hybrid organic/inorganic systems where strong excitonic interactions are desired for light generation, light harvesting, and sensing applications. C polymer nanoparticles (CPNs) attract significant attention for important applications including bioimaging, biosensing, and optoelectronics. One of the most attractive features of CPNs is the convenient tunability and control of their properties through the choice and functionalization of the polymer and the surface modification of nanoparticles. Furthermore, CPNs exhibit low toxicity, and their mechanical stability can be enhanced through cross-linking. Their optical properties arise from the controlled conformational changes of the polymer and their aggregation form rather than the quantum confinement effects, in contrast with inorganic nanoparticles, for example, colloidal semiconductor quantum dots (QDs). As a result of these attractive properties, CPNs find use as alternative color convertors, or molecular beacons, in various biotechnology and optoelectronic applications. The emission of color convertors, including CPNs, can be enhanced via the Förster-type nonradiative energy transfer (NRET) (also dubbed as Förster resonance energy transfer, FRET), which basically relies on the exciton−exciton interactions between the donor and acceptor emitters. For example, polymers, organic dyes, inorganic QDs, and epitaxial quantum wells have been widely investigated for NRET studies. CPNs were also used in similar studies because of their preferably high absorption cross sections. Another important class of materials in optoelectronics is the III-nitrides. They are the main building blocks of today’s UV, blue, green, and white light-emitting diodes. Using these materials, a wide range of spectral regions from the ultraviolet to the green can be covered by controlling their alloy composition. In particular, quantum-well (QW) architectures Received: May 2, 2013 Revised: August 14, 2013 Published: August 14, 2013 Article