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

White emitting polyfluorene functionalized with azide hybridized on near-UV light emitting diode for high color rendering index

Cataloged from PDF version of article.We develop and demonstrate high-quality white light generation that relies on the use of a single-type simple conjugated polymer of polyfluorene functionalized with azide groups (PFA) integrated on a near-UV LED platform. The high-quality white emission from the polyfluorene is achieved by using the azide functionalization to facilitate cross-linking intentionally when cast into solid-state form. Hybridized on n-UV InGaN/GaN LED at 378 nm, the PFA emitters collectively generate a very broad down-converting photoluminescence at longer wavelengths across the entirety of the visible spectrum, yielding high color rendering indices up to 91. (c) 2008 Optical Society of America

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

The use of a nasolabial island flap in vestibulo-sulcoplasty in a patient with recurrent depressed scar on the modiolus

No Abstract

MEASUREMENT OF NOX, SO2, SPM, AND O-3 AT A HIGH-ALTITUDE STATION IN NORTHWESTERN TURKEY

Temporal variation of NO, NO2, SO2, SPM (suspended particulate matter), and O-3 were measured at a high altitude station in the northwestern part of Turkey. The long- and short-term trends in the concentrations of measured parameters were investigated to understand sources contributing to the observed concentrations of these pollutants. Higher concentrations of O-3 during summer months were consistent with higher photochemical production with increased solar flux. Seasonal patterns observed in other parameters were consistent with their source strengths during different periods of the year. O-3 showed a peak at approximately 3 pm, together with SO2 and NO2. SPM, on the other hand, showed a different diurnal pattern with a maximum concentration occurring during night hours. The main sources of O-3, SO2, and NO2 on Mt. Uludag were found to be transported from the town of Bursa and from a nearby ski resort. The vehicular activities on the road which connects the town of Bursa to the ski resort are also an observable source of O-3 and its precursors, but not of SO2 and SPM. High concentrations of O-3 were observed during night hours. Unlike daytime peaks, these peaks were sporadic and did not correlate with the SO2 and NO2. These night-time O-3 concentrations were suspected to be due to injection from the stratosphere

Ozone concentrations at a rural mountain site of northwestern Turkey

Average ozone concentrations at a remote site in the Uludag Mountain of Northwestern Turkey was 29 ppb for a 12 month period. Only 11% of the time 1-h average values exceed 50 ppb. The US Air Quality Standard of 0.12 ppm was not exceeded. The diurnal variations of O3 and NO2 were 27 and 2.3 ppb respectively, during summer 1993, indicating the impact of urban and industrial sources. Highest O3 concentrations were observed under southerly and northerly winds, suggestive of the transport of photochemically produced oxidants from Bursa city and industries and a power plant located downwind of the sampling siteAverage ozone concentrations at a remote site in the Uludag Mountain of Northwestern Turkey was 29 ppb for a 12 month period. Only 11% of the time 1-h average values exceed 50 ppb. The US Air Quality Standard of 0.12 ppm was not exceeded. The diurnal variations of O3 and NO2 were 27 and 2.3 ppb respectively, during summer 1993, indicating the impact of urban and industrial sources. Highest O3 concentrations were observed under southerly and northerly winds, suggestive of the transport of photochemically produced oxidants from Bursa city and industries and a power plant located downwind of the sampling sit