On the origin of high quality white light emission from a hybrid organic/inorganic light emitting diode using azide functionalized polyfluorene

High quality white light generation with high colour rendering index (CRI) was achieved by integrating a cross-linkable azide functionalized polyfluorene derivative, namely poly[(9,9-dihexylfluorene)-co-alt-(9,9-bis(6-azidohexyl) fluorene)] (PFA), as a down-converting fluorescent material on the inorganic n-UV InGaN/GaN LED platform. For comparison, two other polyfluorene based polymers, namely poly[(9,9-dihexylfluorene)-co-alt-(9,9-bis(6-bromohexyl) fluorene)] (PFB) and poly[9,9-dihexyl-9H-fluorene] (PF), were tested for white light generation. While PFA and PF both led to white light generation, PFB fell out of the white region on the chromaticity diagram. Compared to PFA, both of the control groups (PF and PFB) exhibited much lower CRI. To gain a better insight into the mechanisms playing a key role for the generation of such high quality white light in PFA, all of these polymers were further subjected to a series of experiments such as controlled exposure to heat at 220 °C for 2 h under Ar and in air. The polymers PFA and PFB, which include cross-linkable groups, produced broad emission spectra in the region of 430-650 nm upon annealing in the absence of oxygen under Ar atmosphere while almost no change was observed in the emission spectrum of PF without any cross-linkable groups. PFA undergoes cross-linking through the decomposition of azide leading to reactive nitrene species, whereas in PFB cross-linking probably occurs via debromination. This result clearly proved that the broadening can not be attributed only to photo or thermal oxidation, but it is also due to cross-linking. PFA was also exposed to n-UV light from the InGaN/GaN LED to investigate its photostability. In these experiments, the spectral changes in absorbance and emission properties and thermal transitions of these polymers were monitored by FT-IR, UV-Vis and fluorescent spectrometry, and differential scanning calorimetry (DSC). These experiments indicated that PFA provides high quality white light opportunely via cross-linking and remains stable once cross-linking is formed in a solid film. © 2008 The Royal Society of Chemistry

Increased quantum efficiency and reduced red-shift in polymer nanoparticle luminophors

[No abstract available

Photonic devices and systems embedded with nanocyrstals

We review our research work on the development of photonic devices and systems embedded with nanocyrstals for new functionality within EU Phoremost Network of Excellence on nanophotonics. Here we report on CdSe/ZnS nanocrystalbased hybrid optoelectronic devices and systems used for scintillation to enhance optical detection and imaging in the ultraviolet range and for optical modulation via electric field dependent optical absorption and photoluminescence in the visible. In our collaboration with DYO, we also present photocatalytic TiO2 nanoparticles incorporated in solgel matrix that are optically activated in the ultraviolet for the purpose of self-cleaning

White light generation with azide functionalized polyfluorene hybridized on near-UV light emitting diode

We present white light generation using poly[(9,9-dihexylfluorene)-co-alt- (9,9-bis-(6- azidohexyl)fluorene] (PFA) for the first time. Hybridizing PFA on near-UV LED, we demonstrate high color rendering index up to 91.0. © 2007 Optical Society of America

White light generation tuned by dual hybridization of nanocrystals and conjugated polymers

Dual hybridization of highly fluorescent conjugated polymers and highly luminescent nanocrystals (NCs) is developed and demonstrated in multiple combinations for controlled white light generation with high color rendering index (CRI) (> 80) for the first time. The generated white light is tuned using layer-by-layer assembly of CdSe/ZnS core-shell NCs closely packed on polyfluorene, hybridized on near-UV emitting nitride-based light emitting diodes (LEDs). The design, synthesis, growth, fabrication and characterization of these hybrid inorganic-organic white LEDs are presented. The following experimental realizations are reported: (i) layer-by-layer hybridization of yellow NCs (λPL = 580nm) and blue polyfluorene (λPL = 439 nm) with tristimulus coordinates of (x, y) = (0.31, 0.27), correlated color temperature of Tc = 6962 K and CRI of R a = 53.4; (ii) layer-by-layer assembly of yellow and green NCs (λPL = 580 and 540 nm) and blue polyfluorene (λPL = 439 nm) with (x, y) = (0.23, 0.30), Tc = 14395 K and Ra = 65.7; and (iii) layer-by-layer deposition of yellow, green and red NCs (λPL = 580, 540 and 620 nm) and blue polyfluorene (λPL = 439 nm) with (x, y) = (0.38, 0.39), T c = 4052 K and Ra = 83.0. The CRI is demonstrated to be well controlled and significantly improved by increasing multi-chromaticity of the NC and polymer emitters. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft

High-quality white light generation using dually hybridized nanocrystals and conjugated polymers

[No abstract available

Surface-state emission enhancement in white-luminophor CdS nanocrystals using localized plasmon coupling

[No abstract available

Selective enhancement of surface-state emission and simultaneous quenching of interband transition in white-luminophor CdS nanocrystals using localized plasmon coupling

We propose and demonstrate the controlled modification and selective enhancement of surface-state emission in white-luminophor CdS nanocrystals (NCs) by plasmon-coupling them with proximal metal nanostructures. By carefully designing nano-Ag films to match their localized plasmon resonance spectrally with the surface-state emission peak of CdS NCs, we experimentally show that the surface-state emission is substantially enhanced in the visible wavelength, while the interband (band-edge) transition at the shorter wavelength far away from the plasmon resonance is simultaneously significantly suppressed. With such plasmon tuning and consequent strong plasmon coupling specifically for the surface-state transitions, the surface-state emission is made stronger than the band-edge emission. This corresponds to an enhancement factor of 12.7-fold in the ratio of the surface-state peak emission to the band-edge peak emission of the plasmon-coupled film sample compared with that in solution. Such a plasmonic engineering of surface-state emission in trap-rich CdS white nanoluminophors holds great promise for future solid-state lighting. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft