Using high-resolution spectroscopy at cryogenic temperatures for single quantum dots under an external electric bias, we quantitatively show that the quantum-confined Stark effect is the cause of spectral diffusion. As a consequence, spectral fluctuations may be minimized by applying an adequate counter bias.

Spectral diffusion (SD) represents a substantial obstacle toward implementation of solid-state quantum emitters as a source of indistinguishable photons. By performing high-resolution emission spectroscopy for individual colloidal quantum dots at cryogenic temperatures, we prove the causal link between the quantum-confined Stark effect and SD. Statistically analyzing the wavelength of emitted photons, we show that increasing the sensitivity of the transition energy to an applied electric field results in amplified spectral fluctuations. This relation is quantitatively fit to a straightforward model, indicating the presence of a stochastic electric field on a microscopic scale, whose standard deviation is 9 kV/cm, on average. The current method will enable the study of SD in multiple types of quantum emitters such as solid-state defects or organic lead halide perovskite quantum dots, for which spectral instability is a critical barrier for applications in quantum sensing.

A robust algorithm based on cross-correlations and lucky imaging reliably allows the correction of spectrally diffused datasets. This step enables the resolution-limited analysis of the emission fine structure of semiconductor quantum dots (QDs). Bright and dark excitonic transitions are resolved with optimum signal-to-noise ratio, allowing for a precise determination of the angular direction of linear polarization of the different lines. The angular phases between polarization directions are intrinsically connected to the orientations of emission dipoles. This fact provides a tool for accurate numerical computation of the azimuth ϕ and polar angle θ of the QD with respect to the optical axis. Our in-situ characterization of QD fine structure and orientation represents a precise and non-invasive method without requiring specialized equipment beyond a standard luminescence setup. In this way, important information is provided whenever efficient coupling of a quantum emitter to the electromagnetic field is targeted by various nano- and micro-optic strategies.

Catalytic chain growth Suzuki-Miyaura polymerization of an AB-fluorene monomer using isolated (Ini1) or in situ generated (Ini2) Phos-Ph-Pd((Bu3P)-Bu-t)Br as an initiator afforded well-defined heterodifunctional polyfluorenes featuring a phosphonate group (initiating chain end) and a radically polymerizable (Phos-PF8-Sty) or atom transfer radical polymerization (ATRP)-initiating (Phos-PF8-AlkylBr) group (terminating chain end). The resulting Phos-PF8-AlkylBr polymer was directly employed for the growth of a second nonconjugated block by controlled activators regenerated by electron transfer ATRP without the need for further intermediate conversion steps. The PF8 macroinitiator was found to be a viable initiator for the generation of narrowly distributed diblock copolymers with a controlled block length of PF8 and polystyrene, poly(methyl methacrylate), or poly(2-ethylhexyl methacrylate), respectively. Novel conjugated nonconjugated comb polymers were generated by controlled radical copolymerization of PF8 macromonomers, bearing a styrene end group, with styrene or methacrylates. Thereby, it was possible to tune the number of phosphonate moieties per chain between 2 and 15.

Hybrid particles consisting of II-VI semiconductor quantum dots and conjugated polymers are increasingly relevant, but access is limited by the usual step growth nature of polymer formation. We report on a grafting from approach by controlled Pd(II)-mediated polymerization to yield CdSe/CdS nanocrystals with a defined number of polyfluorene chains grown from their surface, as concluded from MALDI-TOF analysis and quantitative end-capping. Further studies underline the importance of matching the monomers' and the surface-bound initiators' reactivity.

Allylboration is a versatile tool for the post-polymerization functionalization of poly(butadiene-co-[4,4,5,5-tetramethyl-2-(3-methyl- 1,3-butadienyl)-1,3,2-dioxaborolane]). Polar functionalized aldehydes HC(O)C6H4(CH2)R (R = Br, NR2, PPh3, P(O)(OEt)(2)) react readily with the allyl boronic acid ester groups in the copolymer without interfering with the reactive double bonds in the polymer backbone. This provides access to stereoregular poly(butadiene) functionalized with a broad range of polar groups. Functionalization proceeds under polymerization conditions and therefore does not require a prior polymer work-up.

AbstractIn the product development of vehicle seat belt systems there is a strong need for the possibility of an isolated component testing that is comparable to real world car crashes. A test bench concept that is able to fulfill this requirement is presented. This test bench mainly consists of a highly dynamic actuator system for which a control scheme is presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

There are well-known theoretical examples that show that stability constraints in nonlinear model predictive control (NMPC) are necessary in order to guarantee closed loop stability. In this paper it is shown that these stability constraints, derived from theory, are also essential in practice. In particular, an experimental study is carried out on a four tank system that illustrates the stability behavior of NMPC.