M. T. Bernius

Bio: M. T. Bernius is an academic researcher. The author has contributed to research in topics: Light-emitting diode & Polyfluorene. The author has an hindex of 2, co-authored 2 publications receiving 664 citations.

High brightness and efficiency blue light-emitting polymer diodes

Abstract: Efficient blue electroluminescence, peaked at 436 nm, is demonstrated from polymer light-emitting diodes operating at high brightness A dioctyl-substituted polyfluorene was used as the emissive layer in combination with a polymeric triphenyldiamine hole transport layer The luminance reaches 600 cd/m2 at a current density of 150 mA/cm2 for a bias voltage of 20 V, corresponding to an efficiency of 025 cd/A and a luminosity of 004 lm/W These values are optimized at a critical emissive layer thickness

Spectral properties of resonant-cavity, polyfluorene light-emitting diodes

Abstract: We report on the fabrication and device properties of light-emitting resonant cavity conjugated-polymer diodes. The microcavity structures were constructed using a dielectric mirror, an indium–tin–oxide anode, a green light-emitting polyfluorene blend, and a metal (cathode) mirror. The best performance was obtained for a composite calcium–aluminum cathode, that combines high reflectivity with a low workfunction. This structure emitted electroluminescence with a linewidth of 12 nm and a maximum brightness of 300 cd m−2 at a bias of 35 V with an efficiency of 0.95 cd A−1.

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.

Endothermic energy transfer: A mechanism for generating very efficient high-energy phosphorescent emission in organic materials

Abstract: Intermolecular energy transfer processes typically involve an exothermic transfer of energy from a donor site to a molecule with a substantially lower-energy excited state (trap). Here, we demonstrate that an endothermic energy transfer from a molecular organic host (donor) to an organometallic phosphor (trap) can lead to highly efficient blue electroluminescence. This demonstration of endothermic transfer employs iridium(III)bis(4,6-di-fluorophenyl)-pyridinato-N,C2′)picolinate as the phosphor. Due to the comparable energy of the phosphor triplet state relative to that of the 4,4′-N,N′-dicarbazole-biphenyl conductive host molecule into which it is doped, the rapid exothermic transfer of energy from phosphor to host, and subsequent slow endothermic transfer from host back to phosphor, is clearly observed. Using this unique triplet energy transfer process, we force emission from the higher-energy, blue triplet state of the phosphor (peak wavelength of 470 nm), obtaining a very high maximum organic light-emi...

Organometallic compounds and emission-shifting organic electrophosphorescence

Abstract: Emissive phosphorescent organometallic compounds are described that produce improved electroluminescence, particularly in the blue region of the visible spectrum. Organic light emitting devices employing such emissive phosphorescent organometallic compounds are also described. Also described is an organic light emitting layer including a host material having a lowest triplet excited state having a decay rate of less than about 1 per second; a guest material dispersed in the host material, the guest material having a lowest triplet excited state having a radiative decay rate of greater than about 1×10 5 or about 1×10 6 per second and wherein the energy level of the lowest triplet excited state of the host material is lower than the energy level of the lowest triplet excited state of the guest material.

Electrochemical determination of the ionization potential and electron affinity of poly(9,9-dioctylfluorene)

Abstract: We report cyclic voltammetry measurements for the blue electroluminescent conjugated polymer poly(9,9-dioctylfluorene). Both oxidation and reduction potentials are determined and thus estimates of both the ionization potential Ip and electron affinity Ea of the polymer are obtained for the same sample under the same experimental conditions. We estimate Ip=5.80 eV and Ea=2.12 eV. These results disagree with the common assumption that Ea is, to good approximation, given by the difference between Ip and the optical gap. Measurements on indium tin oxide/polyfluorene/calcium light emitting diode structures are consistent with the deductions from the electrochemical data.

Interplay of Physical Structure and Photophysics for a Liquid Crystalline Polyfluorene

Abstract: From photophysical evidence, we suggest a structural model based on intrachain ordering that can account for the changes of the absorption spectrum of poly(9,9-dioctylfluorene) (PFO) films under certain physicochemical treatment protocols. We correlate this model to the results of X-ray fiber diffraction experiments.