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Opachich, Y P,Comin, A,Bartelt, A F,Young, A T,Scholl, A,Feng, J,Schmalhorst, J,Shin, H J,Engelhorn, K,Risbud, S H,Reiss, G,Padmore, H A IOP Pub 2010 Journal of Physics, Condensed Matter Vol.22 No.15
<P>The demagnetization dynamics of the Heusler alloy Co<SUB>2</SUB>MnSi was studied using picosecond time-resolved x-ray magnetic circular dichroism. The sample was excited using femtosecond laser pulses. In contrast to the sub-picosecond demagnetization of the metal ferromagnet Ni, substantially slower demagnetization with a time constant of 3.5 ± 0.5 ps was measured. This could be explained by a spin-dependent band gap inhibiting the spin-flip scattering of hot electrons in Co<SUB>2</SUB>MnSi, which is predicted to be half-metallic. A universal demagnetization time constant was measured across a range of pump power levels. </P>
Perovskite energy funnels for efficient light-emitting diodes
Yuan, Mingjian,Quan, Li Na,Comin, Riccardo,Walters, Grant,Sabatini, Randy,Voznyy, Oleksandr,Hoogland, Sjoerd,Zhao, Yongbiao,Beauregard, Eric M.,Kanjanaboos, Pongsakorn,Lu, Zhenghong,Kim, Dong Ha,Sarge Nature Publishing Group 2016 Nature nanotechnology Vol.11 No.10
<P>Organometal halide perovskites exhibit large bulk crystal domain sizes, rare traps, excellent mobilities and carriers that are free at room temperature-properties that support their excellent performance in charge-separating devices. In devices that rely on the forward injection of electrons and holes, such as light-emitting diodes (LEDs), excellent mobilities contribute to the efficient capture of non-equilibrium charge carriers by rare non-radiative centres. Moreover, the lack of bound excitons weakens the competition of desired radiative (over undesired non-radiative) recombination. Here we report a perovskite mixed material comprising a series of differently quantum-size-tuned grains that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture. The materials function as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence non-radiative recombination. We use the new material to build devices that exhibit an external quantum efficiency (EQE) of 8.8% and a radiance of 80 W sr(-1) m(-2). These represent the brightest and most efficient solution-processed near-infrared LEDs to date.</P>
Self-Assembled PbSe Nanowire:Perovskite Hybrids
Yang, Zhenyu,Yassitepe, Emre,Voznyy, Oleksandr,Janmohamed, Alyf,Lan, Xinzheng,Levina, Larissa,Comin, Riccardo,Sargent, Edward H. American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.47
<P>Inorganic semiconductor nanowires are of interest in nano- and microscale photonic and electronic applications. Here we report the formation of PbSe nanowires based on directional quantum dot alignment and fusion regulated by hybrid organic–inorganic perovskite surface ligands. All material synthesis is carried out at mild temperatures. Passivation of PbSe quantum dots was achieved via a new perovskite ligand exchange. Subsequent <I>in situ</I> ammonium/amine substitution by butylamine enables quantum dots to be capped by butylammonium lead iodide, and this further drives the formation of a PbSe nanowire superlattice in a two-dimensional (2D) perovskite matrix. The average spacing between two adjacent nanowires agrees well with the thickness of single atomic layer of 2D perovskite, consistent with the formation of a new self-assembled semiconductor nanowire:perovskite heterocrystal hybrid.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-47/jacs.5b10641/production/images/medium/ja-2015-106416_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b10641'>ACS Electronic Supporting Info</A></P>
Tailoring the Energy Landscape in Quasi-2D Halide Perovskites Enables Efficient Green-Light Emission
Quan, Li Na,Zhao, Yongbiao,Garcí,a de Arquer, F. Pelayo,Sabatini, Randy,Walters, Grant,Voznyy, Oleksandr,Comin, Riccardo,Li, Yiying,Fan, James Z.,Tan, Hairen,Pan, Jun,Yuan, Mingjian,Bakr, Osman American Chemical Society 2017 NANO LETTERS Vol.17 No.6
<P>Organo-metal halide perovskites are a promising platform for optoelectronic applications in view of their excellent charge-transport and bandgap tunability. However, their low photoluminescence quantum efficiencies, especially in low-excitation regimes, limit their efficiency for light emission. Consequently, perovskite light-emitting devices are operated under high injection, a regime under which the materials have so far been unstable. Here we show that, by concentrating photoexcited states into a small subpopulation of radiative domains, one can achieve a high quantum yield, even at low excitation intensities. We tailor the composition of quasi-2D perovskites to direct the energy transfer into the lowest-bandgap minority phase and to do so faster than it is lost to nonradiative centers. The new material exhibits 60% photoluminescence quantum yield at excitation intensities as low as 1.8 mW/cm(2), yielding a ratio of quantum yield to excitation intensity of 0.3 cm(2)/mW; this represents a decrease of 2 orders of magnitude in the excitation power required to reach high efficiency compared with the best prior reports. Using this strategy, we report light-emitting diodes with external quantum efficiencies of 7.4% and a high luminescence of 8400 cd/m(2).</P>