Micro pixel LEDs: Design challenge and implementation for high-resolution headlamps

High-resolution vehicle headlamps represent a future-oriented technology that can be used to increase traffic safety and driving comfort. Typically, selective absorbing of light using a spatial modulator like DMD, LCD or LCoS creates the light distribution of such headlamp systems. A similar effect can be generated by using LED arrays. Its additive principle generates light only in specific segments if necessary. In general, these arrays can be distinguished between conventional LEDs arranged in an array and micro pixel LEDs. Conventional LED arrays characterize by the design (THT or SMD) with typically a few millimeters edge length. In contrast, a micro-pixel LED uses COB technology, in which individual LED dies are packed in a single housing directly next to each other at a distance of a few microns. By increasing the array resolution, the challenges in designing an optical system for high-resolution headlamps rise. High efficiencies and contrasts call for small, accurate lens geometries and negligibly scattered light effects. Due to limited installation space and manufacturing tolerances, compromises have to be made. Ideally, the optics have to be accurate enough to image each pixel of the micro LED with high contrasts and high efficiency and still be too blurry to project the gaps between each pixel. This results in small distances between LED and optics and therefore in diffcult to manufacture radii of curvature. In this paper we specify the challenges to implement micro pixel LEDs in headlamp systems, as well as present the controllability of scattered light effects of these systems. © COPYRIGHT SPI

Konzeption, Realisierung und Verifikation eines automobilen Forschungsscheinwerfers auf Basis von Digitalprojektoren

As far as automotive lighting technoligies are concerned, the question rises in which way different technologies nowadays and in future can be displayed realistically and with high validity while simultaneously saving costs and time. This paper describes the conception and the technical installation of the multifunctional headlighting platform Propix which is supposed to being used for various research activity in the field of automotive lighting physiology

Understanding the Photoexcitation of Room Temperature Ionic Liquids

Photoexcitation of (neat) room temperature ionic liquids (RTILs) leads to the observation of transient species that are reminiscent of the composition of the RTILs themselves. In this minireview, we summarize state‐of‐the‐art in the understanding of the underlying elementary processes. By varying the anion or cation, one aim is to generally predict radiation‐induced chemistry and physics of RTILs. One major task is to address the fate of excess electrons (and holes) after photoexcitation, which implies an overview of various formation mechanisms considering structural and dynamical aspects. Therefore, transient studies on time scales from femtoseconds to microseconds can greatly help to elucidate the most relevant steps after photoexcitation. Sometimes, radiation may eventually result in destruction of the RTILs making photostability another important issue to be discussed. Finally, characteristic heterogeneities can be associated with specific physicochemical properties. Influencing these properties by adding conventional solvents, like water, can open a wide field of application, which is briefly summarized

Photoexcitation of Ge9−^{-} Clusters in THF: New Insights into the Ultrafast Relaxation Dynamics and the Influence of the Cation

We present a comprehensive femtosecond (fs) transient absorption study of the [Ge$_{9}$(Hyp)$_{3}$]$^{-}$ (Hyp = Si(SiMe3)3) cluster solvated in tetrahydrofuran (THF) with special emphasis on intra- and intermolecular charge transfer mechanisms which can be tuned by exchange of the counterion and by dimerization of the cluster. The examination of the visible and the near infrared (NIR) spectral range reveals four different processes of cluster dynamics after UV (267/258 nm) photoexcitation related to charge transfer to solvent and localized excited states in the cluster. The resulting transient absorption is mainly observed in the NIR region. In the UV-Vis range transient absorption of the (neutral) cluster core with similar dynamics can be observed. By transferring concepts of: (i) charge transfer to the solvent known from solvated Na$^{-}$ in THF and (ii) charge transfer in bulk-like materials on metalloid cluster systems containing [Ge$_{9}$(Hyp)$_{3}$]$^{-}$ moieties, we can nicely interpret the experimental findings for the different compounds. The first process occurs on a fs timescale and is attributed to localization of the excited electron in the quasi-conduction band/excited state which competes with a charge transfer to the solvent. The latter leads to an excess electron initially located in the vicinity of the parent cluster within the same solvent shell. In a second step, it can recombine with the cluster core with time constants in the picosecond (ps) timescale. Some electrons can escape the influence of the cluster leading to a solvated electron or after interaction with a cation to a contact pair both with lifetimes exceeding our experimentally accessible time window of 1 nanosecond (ns). An additional time constant on a tens of ps timescale is pronounced in the UV-Vis range which can be attributed to the recombination rate of the excited state or quasi conduction band of Ge$_{9}$$^{-}$. In the dimer, the excess electron cannot escape the molecule due to strong trapping by the Zn cation that links the two cluster cores

Aqueous Conversion of Fructose Phosphate Precursor Nanoparticles into Emissive C-Dot Composite Nanoparticles

[ZrO]$^{2+}$[F6P]$^{2}$− and [Eu(OH)]$^{2}$+[F6P]$^{2}$− precursor nanoparticles (F6P: D-fructose-6-phosphate) are converted in a one-pot, aqueous approach to C-dot@[ZrO]$^{2+}$+[HPO$_{4}$]$^{2-}$ and C-dot@[Eu(OH)]$^{2+}$[HPO$_{4}$]$^{2-}$ composite nanoparticles. Herein, the C-dots (2–3 nm) are embedded in a dense zirconyl/europium phosphate matrix. The resulting composite nanoparticles (40–50 nm) are well-dispersible in water and show blue and red emission. A one-pot, fully water-based synthesis of blue- and red-emitting C-dots is presented. To this concern, [ZrO]$^{2+}$[F6P]$^{2}$− and [Eu(OH)]$^{2}$+[F6P]$^{2}$− precursor nanoparticles (F6P: D-fructose-6-phosphate) are prepared in water and converted to C-dot@[ZrO]$^{2+}$+[HPO$_{4}$]$^{2-}$ and C-dot@[Eu(OH)]$^{2+}$[HPO$_{4}$]$^{2-}$ composite nanoparticles in boiling water (100 °C) via microwave heating. Composition, structure, and fluorescence of the composite nanoparticles are validated by different analytical methods (e. g., FT-IR, EA, TG, DLS, SEM, TEM, EDXS). The resulting aqueous suspensions are characterized by high colloidal stability and intense emission. Specifically, C-dot@[Eu(OH)]$^{2+}$[HPO$_{4}$]$^{2-}$ exhibits Eu$^{3+}$-type red emission in water. The one-pot water-based synthesis with fructose-containing precursor nanoparticles and the structure of the phosphate-stabilized C-dot composite nanoparticles are reported for the first time

Directed Electron Transfer in Flavin Peptides with Oligoproline‐Type Helical Conformation as Models for Flavin‐Functional Proteins

To mimic the charge separation in functional proteins we studied flavin‐modified peptides as models. They were synthesized as oligoprolines that typically form a polyproline type‐II helix, because this secondary structure supports the electron transfer properties. We placed the flavin as photoexcitable chromophore and electron acceptor at the N‐terminus. Tryptophans were placed as electron donors to direct the electron transfer over 0–3 intervening prolines. Spectroscopic studies revealed competitive photophysical pathways. The reference peptide without tryptophan shows dominant non‐specific ET dynamics, leading to an ion pair formation, whereas peptides with tryptophans have weak non‐specific ET and intensified directed electron transfer. By different excitation wavelengths, we can conclude that the corresponding ion pair state of flavin within the peptide environment has to be energetically located between the S$_{1}$ and S$_{4}$ states, whereas the directed electron transfer to tryptophan occurs directly from the S$_{1}$ state. These photochemical results have fundamental significance for proteins with flavin as redoxactive cofactor

Au20_{20} (t^{t} Bu3_{3} P)8_{8}: A Highly Symmetric Metalloid Gold Cluster in Oxidation State 0

Metalloid gold clusters have unique properties with respect to size and structure and are key intermediates in studying transitions between molecular compounds and the bulk phase of the respective metal. In the following, the synthesis of the all-phosphine protected metalloid cluster Au$_{20}$ ($^{t}$ Bu$_{3}$ P)$_{8}$, solely built from gold atoms in the oxidation state of 0 is reported. Single-crystal X-ray analysis revealed a highly symmetric hollow cube-octahedral arrangement of the gold atoms, resembling gold bulk structure. Quantum-chemical calculations illustrated the cluster can be described as a 20-electron superatom. Optical properties of the compound have shown molecular-like behavior

Cooling therapy for acute stroke

Abstract BACKGROUND: Recent studies in acute stroke patients have shown an association between body temperature and prognosis. OBJECTIVES: Our objective was to assess the effects of cooling when applied to patients with acute ischaemic stroke or primary intracerebral haemorrhage. SEARCH STRATEGY: We searched the Cochrane Stroke Group's trial register (last searched in March 1999), plus MEDLINE searched up to November 1998 and EMBASE searched from January 1980 to November 1998. We contacted investigators, pharmaceutical companies and manufacturers of cooling equipment in this field. SELECTION CRITERIA: All completed randomised controlled trials or controlled clinical trials, published or unpublished, where cooling therapy (therapy given by physical devices or antipyretic drugs primarily to lower body temperature independently of basal temperature at the beginning of treatment) was applied up to two weeks of an acute ischaemic stroke or primary intracerebral haemorrhage. DATA COLLECTION AND ANALYSIS: Two reviewers independently searched for relevant trials. MAIN RESULTS: No randomised trials or controlled trials were identified; one placebo-controlled trial of metamizol is currently underway. REVIEWER'S CONCLUSIONS: There is currently no evidence from randomised trials to support the routine use of physical or chemical cooling therapy in acute stroke. Since experimental studies showed a neuroprotective effect of hypothermia in cerebral ischaemia, and hypothermia appears to improve the outcome in patients with severe closed head injury, trials with cooling therapy in acute stroke are warranted

Photochemical Action Plots Map Orthogonal Reactivity in Photochemical Release Systems

The wavelength-by-wavelength resolved photoreactivity of two photo-caged carboxylic acids, i. e. 7-(diethylamino)-coumarin- and 3-perylene-modified substrates, is investigated via photochemical action plots. The observed wavelength-dependent reactivity of the chromophores is contrasted with their absorption profile. The photochemical action plots reveal a remarkable mismatch between the maximum reactivity and the absorbance. Through the action plot data, the study is able to uncover photochemical reactivity maxima at longer and shorter wavelengths, where the molar absorptivity of the chromophores is strongly reduced. Finally, the laser experiments are translated to light emitting diode (LED) irradiation and show efficient visible-light-induced release in a near fully wavelength-orthogonal, sequence-independent fashion (λLED1 = 405 nm, λLED2 = 505 nm) with both chromophores in the same reaction solution. The herein pioneered wavelength orthogonal release systems open an avenue for releasing two different molecular cargos with visible light in a fully orthogonal fashion

Experimental and Theoretical Study of the Ultrafast Dynamics of a Ni2_2Dy2_2-Compound in DMF After UV/Vis Photoexcitation

We present a combined experimental and theoretical study of the ultrafast transient absorption spectroscopy results of a {Ni$_{2}$Dy$_{2}$}-compound in DMF, which can be considered as a prototypic molecule for single molecule magnets. We apply state-of-the-art ab initio quantum chemistry to quantitatively describe the optical properties of an inorganic complex system comprising ten atoms to form the chromophoric unit, which is further stabilized by surrounding ligands. Two different basis sets are used for the calculations to specifically identify two dominant peaks in the ground state. Furthermore, we theoretically propagate the compound\u27s correlated many-body wavefunction under the influence of a laser pulse as well as relaxation processes and compare against the time-resolved absorption spectra. The experimental data can be described with a time constant of several hundreds of femtoseconds attributed to vibrational relaxation and trapping into states localized within the band gap. A second time constant is ascribed to the excited state while trap states show lifetimes on a longer timescale. The theoretical propagation is performed with the density-matrix formalism and the Lindblad superoperator, which couples the system to a thermal bath, allowing us to extract relaxation times from first principles