Repository hosted by TU Delft Library

In this paper we report on the effect of hydroxyl (OH) groups on the photoluminescence in the near IR (1.5 and 1.3 μm) in rare earth (Er, Pr)-doped glasses. The 1.5 μm emission of Er-doped phosphate glasses was studied, before and after a special heat treatment. The luminescent lifetime of the 1.5 μm emission increases substantially, typically from 3 ms up to 7.2 ms for a 2 mole% Er 2O3-doped phosphate glass, due to the controlled heat treatment. The increase in lifetime is ascribed to a decrease in OH-concentration, which is confirmed by IR-absorption spectroscopy. The quenching by OH is described by a simplified quenching model, which predicts the 1.5 μm emission lifetime as a function of Er-concentration with the OH-concentration as parameter. It appears that the larger part of the OH groups is coupled to Er ions and thus acts as quenching center. Photoluminescence quenching by OH groups is also reported for the 1.3 μm emission of Pr in GeS2-glasses: In pure OH-free GeS2 glass the 1.3 μm emission lifetime is as high as 350 μs, for a 400 ppm dopant level. In GeS2 glasses containing only small amounts of OH (approximately 100 ppm), this lifetime is less than 200 μs. Both examples demonstrate that for the fabrication of efficient glass optical amplifiers at the telecommunication windows 1.3 and 1.5 μm, the OH-impurity level of the host glass must be kept as low as possible.

Halide perovskites have been gaining considerable attention recently for use in light-emitting applications, due to their bandgap tunability, color purity and low cost fabrication methods. However, current fabrication techniques limit the processing to small-area devices. Here, we show that a facile N 2 gas-quenching technique can be used to make methylammonium lead bromide-based perovskite light-emitting diodes (PeLEDs) with a peak luminance of 6600 cd m ?2 and a current efficiency of 7.0 cd A ?1 . We use this strategy to upscale PeLEDs to large-area substrates (230 cm 2 ) by developing a protocol for slot-die coating combined with gas-quenching. The resulting large area devices (9 devices of each 4.46 cm 2 per substrate) with three slot-die coated layers exhibit uniform emission with a peak luminance of 550 cd m ?2 and a current efficiency of 2.6 cd A ?1 . The reasons for the reduced performance and improvement routes are discussed. These results mark a vital step towards scalable manufacturing techniques for PeLEDs.

Polymer-fullerene bilayer heterostructures are suited to study excitonic processes in conjugated polymers. Excitons are efficiently quenched at the polymer-fullerene interface, whereas the polymer-vacuum interface is often considered as an exciton-reflecting interface. Here, we report about efficient exciton quenching close to the polymer-vacuum interface of spin-coated MDMO-PPV (poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylenevinylene]) films. The quenching efficiency is estimated to be as high as that of the polymer-fullerene interface. This efficient quenching is consistent with enhanced intermolecular interactions close to the polymer-vacuum interface due to the formation of a "skin layer" during the spin-coating procedure. In the skin layer, the polymer density is higher; that is, the intermolecular distances are shorter than in the rest of the film. The effect of exciton quenching at the polymer-vacuum interface should be taken into account when the thickness of the polymer film is on the order of the exciton diffusion length; in particular, in the determination of the exciton diffusion length. © 2009 American Chemical Society.

We present results and a discussion of highly efficient polymer Light-Emitting Diodes (polymer LEDs, PLEDs). The external quantum efficiency in current standard devices reaches up to 2-4% only. We have explored two routes to enhance this value. In the first route, PEDOT/PSS is replaced with a novel anode or hole injection layer. The efficiency with some Light Emitting Polymers (LEP) is improved significantly, resulting in an efficacy of 35 cd/A for a yellow emitting poly-(para-phenylene-vinylene) and 20 cd/A for a blue emitting poly-(spirobifluorene). We attribute the major improvement compared to standard devices, where about 10 and 5 cd/A are obtained, respectively, to a combination of improved exciton formation efficiency and light out-coupling efficiency, and to less quenching of the radiative decay under actual device operating conditions. In the second route, we developed a new host polymer with high triplet energy such that transition metal-based green-emitting phosphorescent dyes can be used without significant back transfer of triplet excitons to the polymer host. First results using this system showed about 25 cd/A using a soluble green Ir-based emitter. Importantly, all data are obtained in a standard two-layer device of a hole transport/injection layer and the LEP.

We demonstrate a solution processed bi-layer PLED based on poly(p-phenylene vinylene) derivatives using orthogonal solvents. To lower the voltage drop the hole transport layer (HTL) based on poly[2,5-bis(2-ethylhexyloxy)-co-2,5- bis(butoxy)-1,4-phenylenevinylene] (BEH/BB-PPV (1:3)) is doped with tetracyano-tetrafluoro-quinodimethane (F4TCNQ). The conductivity of BEH/BB-PPV (1:3) was observed to increase by two orders of magnitude upon doping with F4TCNQ. The doped HTL was observed to lower the operating voltage of a double layer PLED, but suffers from additional quenching by the dopant at higher voltages due to the lack of an electron blocking functionality. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Messenger RNA levels change on a minutes scale due to both degradation and de novo transcription. Consequently, alterations in the transcript profiles that are not representative for the condition of interest are easily introduced during sample harvesting and work-up. In order to avoid these unwanted changes we have validated a - 45°C methanol-based quenching method for obtaining reliable and reproducible 'snapshot' samples of Lactobacillus plantarum cells for transcriptome analyses. Transcript profiles of cells harvested with the quenching method were compared with transcript profiles of cells that were harvested according to two different commonly applied protocols. Significant differences between the transcript profiles of cells harvested by the different methods from the same steady-state culture were observed. In total, 42 genes or operons were identified from which the transcript levels were altered when the cells were not immediately quenched upon harvesting. Among these, several have previously been associated with cold-shock response. Furthermore, the reproducibility of transcript profiles improved, as indicated by the fact that the variation in the data sets obtained from the quenched cells was smaller than in the data sets obtained from the cells that were harvested under non-quenched conditions. © 2005 Elsevier B.V. All rights reserved.

Microbial production strains are currently improved using a combination of random and targeted approaches. In the case of a targeted approach, potential bottlenecks, feed-back inhibition, and side-routes are removed, and other processes of interest are targeted by overexpressing or knocking-out the gene(s) of interest. To date, the selection of these targets has been based at its best on expert knowledge, but to a large extent also on 'educated guesses' and 'gut feeling'. Therefore, time and thus money is wasted on targets that later prove to be irrelevant or only result in a very minor improvement. Moreover, in current approaches, biological processes that are not known to be involved in the formation of a specific product are overlooked and it is impossible to rank the relative importance of the different targets postulated. Metabolomics, a technology that involves the non-targeted, holistic analysis of the changes in the complete set of metabolites in the cell in response to environmental or cellular changes, in combination with multivariate data analysis (MVDA) tools like principal component discriminant analysis and partial least squares, allow the replacement of current empirical approaches by a scientific approach towards the selection and ranking of targets. In this review, we describe the technological challenges in setting up the novel metabolomics technology and the principle of MVDA algorithms in analyzing biomolecular data sets. In addition to strain improvement, the combined metabolomics and MVDA approach can also be applied to growth medium optimization, predicting the effect of quality differences of different batches of complex media on productivity, the identification of bioactives in complex mixtures, the characterization of mutant strains, the exploration of the production potential of strains, the assignment of functions to orphan genes, the identification of metabolite-dependent regulatory interactions, and many more microbiological issues. © Society for Industrial Microbiology 2005.

We present an all-solution processed polymer light-emitting diode (PLED) using spincoated zinc oxide (ZnO) and vanadium pentoxide (V2O5) as electron and hole injecting contact, respectively. We compare the performance of these devices to the standard PLED design using PEDOT:PSS as anode and Ba/Al as cathode. We show that the all-solution processed PLEDs have an equal performance as compared to the standard design directly after fabrication. However, the ambient stability of the PLEDs with spincoated transition metal oxide electrodes is exceptionally good in comparison to the standard design. © 2012 Elsevier B.V. All rights reserved.

N-type doping of poly(2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene) (MEH-PPV) with decamethylcobaltocene (DMC) strongly improves the electron transport due to filling of the electron traps. Unexpectedly, the n-type doping simultaneously suppresses the hole transport in MEH-PPV. We demonstrate that this strong reduction of the hole transport originates from unionized DMC molecules that act as hole traps. This hole trapping effect explains why the current of a DMC-doped MEH-PPV polymer light-emitting diode is orders of magnitude lower than that of the undoped device. © 2011 Wiley Periodicals, Inc.