Harald Meyer

Electroluminescence from multilayer organic light‐emitting diodes using poly(methylphenylsilane) as hole transporting material

We have investigated the optical and electrical properties of polysilane‐based multilayer electroluminescent (EL) devices, utilizing poly(methylphenylsilane) (PMPS) as the hole transporting material, in order to elucidate the mechanism of EL emission in these devices. The EL devices which we fabricated have two or three functional organic layers. These layers are composed of a PMPS layer as well as a 3‐(2’‐Benzothiazolyl)‐7‐diethylaminocoumarin (Coumarin 6) doped polystyrene (PS) layer and/or a tris‐(8‐hydroxyquinoline) aluminum (Alq3) layer. An indium‐tin‐oxide‐coated glass and an Al electrode were used as the hole and the electron injecting electrode, respectively. On the basis of a combined analysis of the basic characteristics of these devices, photoexcited fluorescence spectra and decay curves as well as the band diagram of these devices, we concluded that the recombination of charge carriers and the EL emission in the three‐layer device occur both in the Coumarin 6:PS and the evaporated Alq3 layers.

Primitive central idempotents of finite group rings of symmetric groups

Let p be a prime. We denote by S n the symmetric group of degree n, by An the alternating group of degree n and by F p the field with p elements. An important concept of modular representation theory of a finite group G is the notion of a block. The blocks are in one-to-one correspondence with block idempotents, which are the primitive central idempotents of the group ring F q G, where q is a prime power. Here, we describe a new method to compute the primitive central idempotents of F q G for arbitrary prime powers q and arbitrary finite groups G. For the group rings F p S n of the symmetric group, we show how to derive the primitive central idempotents of F P S n-P from the idempotents of F p S n . Improving the theorem of Osima for symmetric groups we exhibit a new subalgebra of F p S n which contains the primitive central idempotents. The described results are most efficient for p = 2. In an appendix we display all primitive central idempotents of F 2 S n and F 4 A n for n ≤ 50 which we computed by this method.

CHARGE CARRIER AND EXCITON DYNAMICS IN POLYSILANE-BASED MULTILAYER LIGHT-EMITTING DIODES AS MONITORED WITH ELECTROLUMINESCENCE

Abstract By using two modes of excitation, optical excitation and current excitation, we have clarified the device physics in operation of multilayer organic light-emitting diodes utilizing poly(methylphenylsilane) as a hole transporting material, focusing on the dynamics of charge carriers injected from electrodes and of excitons generated by the charge carrier recombination.

Measurement of the mobility edge of poly(p-phenylenevinylene) with photobleaching experiments

Abstract A picosecond pump-probe technique employing one pulse with a white continuum spectrum has been used to study the photobleaching of the lowest singlet transition in poly( p -phenylenevinylene) (PPV). The experimental results show that a well-defined photon energy exists at which the saturation properties change abruptly. We interpret this photon energy in terms of a mobility edge for optical excitations, which is located at an energy of 2.38 eV above the ground state.