Franz P. Wenzl

Bio: Franz P. Wenzl is an academic researcher from Joanneum Research. The author has contributed to research in topics: Light-emitting diode & Phosphor. The author has an hindex of 19, co-authored 64 publications receiving 1083 citations. Previous affiliations of Franz P. Wenzl include Graz University of Technology & University of Graz.

The Effect of the Phosphor Particle Sizes on the Angular Homogeneity of Phosphor-Converted High-Power White LED Light Sources

Abstract: Based on optical ray tracing, we discuss the effect of the phosphor particle sizes on the angular homogeneity of the light emitted from phosphor-converted LEDs. Since the blue LED and the yellow-converted light have rather different emission characteristics, which have to be harmonized to one another by the scattering processes within the color conversion element, the phosphor particle size turns out to be an essential parameter in order to attain angular homogeneity. This can be attributed, on the one hand, to the number of scattering processes within a specific unit volume for a given phosphor concentration, and on the other hand, to the specific scattering functions, both of which depend on the phosphor particle diameter.

Tailoring of the Color Conversion Elements in Phosphor-Converted High-Power LEDs by Optical Simulations

Abstract: Ray-tracing simulations are used to identify the demands for angular homogeneity of the white light emitted from phosphor-converted white light-emitting diodes having color conversion elements (CCEs) of constant thickness. The simulations reveal that a constant thickness of the CCE by itself is not sufficient for a homogeneous white light emission. Rather the height and the broadness of the CCE as well as the phosphor concentration have to be precisely adjusted in order to assure a homogeneous white light emission.

The Influence of the Phase Morphology on the Optoelectronic Properties of Light‐Emitting Electrochemical Cells

Abstract: We report on the morphological aspects of thin films prepared from a blue–green light-emitting conjugated polymer, (methyl-substituted ladder-type poly(p-phenylene, mLPPP)), blended with a solid-state electrolyte composed either by a crown ether, dicyclohexano-18-crown-6 (DCH18C6), or a high-molecular-weight poly(ethylene oxide) (HMWPEO), and a Li salt, lithium trifluoromethanesulfonate (LiCF3SO3, Li triflate (LiTf)), as they have been successfully applied in light-emitting electrochemical cells (LECs). The surface morphologies of the blend layers were investigated using atomic force microscopy (AFM) in tapping mode, and the ion distribution was probed using X-ray analysis by means of energy-dispersive X-ray spectrometry (EDXS) in the scanning electron microscope (SEM). We show that the two different phase-separation processes, the complexation tendencies of the ionic species as well as the ionic transport numbers, have tremendous influence on the performances of the corresponding LECs, revealing either rectifying or symmetric optoelectronic characteristics in forward and reverse bias directions. This opens up new possibilities for tuning the optoelectronic properties of ion-supported organic electronic devices.

Conjugated polymer-based chemical sensors.

Abstract: When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

Polymer‐Fullerene Bulk‐Heterojunction Solar Cells

Abstract: Solution-processed bulk-heterojunction solar cells have gained serious attention during the last few years and are becoming established as one of the future photovoltaic technologies for low-cost power production. This article reviews the highlights of the last few years, and summarizes today's state-of-the-art performance. An outlook is given on relevant future materials and technologies that have the potential to guide this young photovoltaic technology towards the magic 10% regime. A cost model supplements the technical discussions, with practical aspects any photovoltaic technology needs to fulfil, and answers to the question as to whether low module costs can compensate lower lifetimes and performances.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

The electroluminescence of organic materials

Abstract: This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

Materials for Fluorescence Resonance Energy Transfer Analysis: Beyond Traditional Donor-Acceptor Combinations

Abstract: The use of Forster or fluorescence resonance energy transfer (FRET) as a spectroscopic technique has been in practice for over 50 years. A search of ISI Web of Science with just the acronym "FRET" returns more than 2300 citations from various areas such as structural elucidation of biological molecules and their interactions, in vitro assays, in vivo monitoring in cellular research, nucleic acid analysis, signal transduction, light harvesting and metallic nanomaterials. The advent of new classes of fluorophores including nanocrystals, nanoparticles, polymers, and genetically encoded proteins, in conjunction with ever more sophisticated equipment, has been vital in this development. This review gives a critical overview of the major classes of fluorophore materials that may act as donor, acceptor, or both in a FRET configuration. We focus in particular on the benefits and limitations of these materials and their combinations, as well as the available methods of bioconjugation.