Close similarity of the electronic structure and electron correlation in gas-phase and solid C60\mathrm{C_{60}}

We present a study of the electronic structure and electron correlation effects in gas-phase and solid C$_{60}$ clusters. Direct in situ comparison of C 1s absorption spectra taken in the gas phase with those from solid C$_{60}$ reveals a close similarity. This is also true for the shake-up satellites in the C 1s x-ray-photoelectron spectrum. The main conclusions are that solid-state interactions play only a minor role in this new material, and electron correlation effects are predominantly intramolecular

Fragmentation of small molecules following soft x-ray excitation

Soft x-ray excitation involving C 1s electrons in CO and acetone, (CH/sub 3/)/sub 2/CO, is found to result in ionic fragmentation of the original molecule. The fragmentation pattern changes whether the C 1s electron get ionized, excited into a Rydberg-line orbital or into an antibonding ..pi..* molecular orbital. Also the fragmentation occurs specifically around the site of the carbon atom where the optical excitation takes place. Based on these observations one might consider the use of tunable soft x-rays to stimulate chemical reactions

Oriented phosphorescent emitters boost OLED efficiency

The orientation distribution of the emissive sites in a phosphorescent Organic LED has been measured utilizing two independent optical methods. In contradiction to common expectations we find a clearly non-isotropic, predominantly parallel emitter orientation in the well-known triplet emitting guest-host system of Ir(MDQ)2(acac) blended in an alpha-NPD matrix. This result emphasizes the necessity of more sophisticated assumptions on active emitter properties in quantitative optical OLED analysis, and demonstrates a highly promising approach for OLED efficiency optimization

Evidence for non-isotropic emitter orientation in a red phosphorescent organic light-emitting diode and its implications for determining the emitter's radiative quantum efficiency

The efficiency of organic light-emitting diodes is limited as only a fraction of the consumed electrical power is converted into light that is finally extracted to air. Especially, the radiative quantum efficiency of the guest-host system is of interest and should be close to unity to achieve highly efficient devices. We show that the red phosphorescent emitter Ir(MDQ) 2(acac) doped in an -NPD matrix exhibits a profound non-isotropic dipole orientation. Ignoring this feature leads to a significant overestimation of the emitter efficiency. Furthermore, we demonstrate the huge potential for efficiency enhancement of mainly parallel emitter orientation in phosphorescent organic light-emitting diodes