On the formation mechanism for electrically generated exciplexes in a carbazole–pyridine copolymer

Although carbazole‐containing copolymers are frequently used as hole‐transporting host materials for polymer organic light‐emitting diodes (OLEDs), they often suffer from the formation of undesired exciplexes when the OLED is operated. The reason why exciplexes sometimes form for electrical excitation, yet not for optical excitation is not well understood. Here, we use luminescence measurements and quantum chemical calculations to investigate the mechanism of such exciplex formation for electrical excitation (electroplex formation) in a carbazole–pyridine copolymer. Our results suggest that the exciplex is formed via a positively charged interchain precursor complex. This complex is stabilized by interactions that involve the nitrogen lone pairs on both chain segments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

The influence of the conduction electrons on the EFG in amorphous intermetallic alloys

The quadrupole splitting in alloys is determined by the structural and electronic properties of the alloy. Only in cases where the density of states at the Fermi level is constant or known as a function of the concentration, relevant structural information can be obtained from the quadrupole splitting.     

Longitudinal field quenching studies in KCl and KBr — Evidence for a precursor muonium state

The repolarization of μ⁺ in a longitudinal field as a function of field strength has been measured at various temperatures in KCl and KBr single crystals. The data at room temperature in KCl are essentially in agreement with Ivanteret al. /1/ and Nishiyamaet al. /5/. The obtained quenching curves can be reasonably fitted by assuming that the long lived muonium state, seen directly in transverse field experiments by Kieflet al. /4/, is preceded by another short lived muonium state with reduced hf-coupling. It is also necessary to allow for electron spin exchange in the precursor state. The model fits yield the hyperfine frequency of the precursor state, its chemical lifetime and an electron spin flip rate. It is speculated that the precursor state and the temperature dependence of the fitted parameters reflect the early history of the μ⁺ in its terminal spur.     

Development of a digital freeprogrammable function generator for high precision double motion Mössbauer-drives

Construction and use of a function generator are presented. The flexible outline allows a high precision control for all required velocity profiles.