Entity

Time filter

Source Type

Aachen, Germany

Durach D.,Ludwig Maximilians University of Munich | Neudert L.,Ludwig Maximilians University of Munich | Schmidt P.J.,Lumileds Germany GmbH | Oeckler O.,University of Leipzig | Schnick W.,Ludwig Maximilians University of Munich
Chemistry of Materials | Year: 2015

Due to the relationship between structure and luminescence properties, detailed crystal structure determination for microcrystalline phosphors is necessary for a profound understanding of materials properties. The yellow phosphor La3BaSi5N9O2:Ce3+ (λmax = 578 nm; fwhm ∼4700 cm-1) was characterized by a combination of transmission electron microscopy (TEM) and synchrotron microfocus diffraction as only agglomerates of crystals with a maximum size of a few μm could be obtained yet. La3BaSi5N9O2:Ce3+ was synthesized from LaF3, La(NH2)3, BaH2, Si(NH)2, and CeF3 in a radio frequency furnace. It crystallizes in space group Pmn21 (no. 31) with a = 9.5505(8), b = 19.0778(16), c = 12.1134(9) Å, and Z = 8. Its interrupted three-dimensional tetrahedra network contains zehner and dreier rings of vertex-sharing SiN4 and SiN2O2 tetrahedra. The crystal structure was confirmed by high-resolution TEM and Z-contrast scanning TEM. The element distribution was derived by bond-valence sum calculations. The infrared spectrum proves the absence of N-H bonds (Figure Presented). © 2015 American Chemical Society. Source


O'Connor A.P.,Max Planck Institute for Nuclear Physics | Becker A.,Max Planck Institute for Nuclear Physics | Blaum K.,Max Planck Institute for Nuclear Physics | Breitenfeldt C.,Max Planck Institute for Nuclear Physics | And 25 more authors.
Physical Review Letters | Year: 2016

We have studied the photodissociation of CH+ in the Cryogenic Storage Ring at ambient temperatures below 10 K. Owing to the extremely high vacuum of the cryogenic environment, we were able to store CH+ beams with a kinetic energy of ∼60 keV for several minutes. Using a pulsed laser, we observed Feshbach-type near-threshold photodissociation resonances for the rotational levels J=0-2 of CH+, exclusively. In comparison to updated, state-of-the-art calculations, we find excellent agreement in the relative intensities of the resonances for a given J, and we can extract time-dependent level populations. Thus, we can monitor the spontaneous relaxation of CH+ to its lowest rotational states and demonstrate the preparation of an internally cold beam of molecular ions. © 2016 American Physical Society. Source


Bhardwaj J.,Trimble | Peddada R.,Trimble | Spinger B.,Lumileds Germany GmbH
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

High power LEDs were introduced in automotive headlights in 2006-2007, for example as full LED headlights in the Audi R8 or low beam in Lexus. Since then, LED headlighting has become established in premium and volume automotive segments and beginning to enable new compact form factors such as distributed low beam and new functions such as adaptive driving beam. New generations of highly versatile high power LEDs are emerging to meet these application needs. In this paper, we will detail ongoing advances in LED technology that enable revolutionary styling, performance and adaptive control in automotive headlights. As the standards which govern the necessary lumens on the road are well established, increasing luminance enables not only more design freedom but also headlight cost reduction with space and weight saving through more compact optics. Adaptive headlighting is based on LED pixelation and requires high contrast, high luminance, smaller LEDs with high-packing density for pixelated Matrix Lighting sources. Matrix applications require an extremely tight tolerance on not only the X, Y placement accuracy, but also on the Z height of the LEDs given the precision optics used to image the LEDs onto the road. A new generation of chip scale packaged (CSP) LEDs based on Wafer Level Packaging (WLP) have been developed to meet these needs, offering a form factor less than 20% increase over the LED emitter surface footprint. These miniature LEDs are surface mount devices compatible with automated tools for L2 board direct attach (without the need for an interposer or L1 substrate), meeting the high position accuracy as well as the optical and thermal performance. To illustrate the versatility of the CSP LEDs, we will show the results of, firstly, a reflector-based distributed low beam using multiple individual cavities each with only 20mm height and secondly 3x4 to 3x28 Matrix arrays for adaptive full beam. Also a few key trends in rear lighting and impact on LED light source technology are discussed. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. Source


Marchuk A.,Ludwig Maximilians University of Munich | Wendl S.,Ludwig Maximilians University of Munich | Imamovic N.,Ludwig Maximilians University of Munich | Tambornino F.,Ludwig Maximilians University of Munich | And 3 more authors.
Chemistry of Materials | Year: 2015

The isotypic nitridophosphates Ba3P5N10X (X = Cl, I) have been synthesized by high-temperature reaction under pressures between 1 and 5 GPa. The crystal structures of both compounds were solved and refined using single-crystal X-ray diffraction data. Accuracy of the structure determination as well as phase purity of the products were confirmed by Rietveld refinement and FTIR spectroscopy. The band gap values (4.0-4.3 eV) for the direct transitions were determined from UV-vis data using the Kubelka-Munk function and were confirmed by DFT calculations. Both compounds crystallize in the Ba3P5N10Br structure type (space group Pnma (No. 62), Z = 8; Ba3P5N10Cl, a = 12.5182(5) Å, b = 13.1798(5) Å, c = 13.7676(6) Å, R1 = 0.0214, wR2 = 0.0526; Ba3P5N10I, a = 12.6311(7) Å, b = 13.2565(8) Å, c = 13.8689(8) Å, R1 = 0.0257, wR2 = 0.0586) with a tetrahedra network being analogous to the topology of the JOZ zeolite structure type. The crystal structure is built up of all-side vertex-sharing PN4 tetrahedra leading to a zeolite-like framework with three-dimensional achter-ring channels containing alternately Ba and respective halide atoms. The condensed dreier-, vierer-, and sechser-rings form two different composite building units made up of 344286-cages. Upon being doped with Eu2+, the title compounds exhibit intriguing luminescence properties, which were compared with that of Ba3P5N10Br:Eu2+. Upon excitation by near-UV light, nonsaturated color luminescence from multiple emission centers was observed in the orange (X = Cl) and cyan to amber (X = I) spectral range of the visible spectrum. © 2015 American Chemical Society. Source


Strobel P.,Ludwig Maximilians University of Munich | Schmiechen S.,Ludwig Maximilians University of Munich | Siegert M.,Ludwig Maximilians University of Munich | Tucks A.,Lumileds Germany GmbH | And 2 more authors.
Chemistry of Materials | Year: 2015

Eu2+- as well as Ce3+-doped Ba[Li2(Al2Si2)N6] and its related Mg-substituted compounds Ba[(Mg2-xLix) (Al4-xSix)N6]:Eu2+ (x = 0-2) with x = 1.6, 1.8 have been synthesized by metathesis reactions in tantalum ampules. Crystal structures were solved and refined from single-crystal X-ray diffraction data. All three compounds crystallize in tetragonal space group P4/ncc (no. 130) (Z = 4, Ba[Li2(Al2Si2)N6]:Eu2+: a = 7.8282(4), c = 9.9557(5) Å, R1 = 0.0144, wR2 = 0.0366). Their crystal structures, exhibiting the novel framework topology whj, consist of a highly condensed anionic tetrahedra network of disordered (Li/Mg)N4 and (Al/Si)N4 units connected to each other by common edges and corners. The degree of condensation (i.e., atomic ratio (Al,Li,Mg,Si):N) is κ = 1. The Ba2+-position is coordinated eight-fold by N3- in form of a truncated square pyramid. Upon doping with Eu2+, narrow-band emission in the green to yellow spectral range is observed (λem = 532-562 nm, fwhm ≈ 1962 cm-1). Ce3+-doped crystals of Ba[Li2(Al2Si2)N6] show blue emission (λem = 468; 507 nm). According to the tunability of the narrow-band green emission, application in LED-backlight liquid crystal displays appears promising. (Figure Presented). © 2015 American Chemical Society. Source

Discover hidden collaborations