Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn(4+) as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.

Physical and optical properties of binary amorphous selenium-antimony thin films

A series of promising multifunctional lanthanide single-molecule magnets (SMMs). Lanthanide luminescence under a pulsed magnetic field for SMMs is examined for the first time.

This work reports on incorporation of spectrally tuned gold/silica (Au/SiO2) core/shell nanospheres and nanorods into the inverted perovskite solar cells (PVSC). The band gap of hybrid lead halide iodide (CH3NH3PbI3) can be gradually increased by replacing iodide with increasing amounts of bromide, which can not only offer an appreciate solar radiation window for the surface plasmon resonance effect utilization, but also potentially result in a large open circuit voltage. The introduction of localized surface plasmons in CH3NH3PbI2.85Br0.15‐based photovoltaic system, which occur in response to electromagnetic radiation, has shown dramatic enhancement of exciton dissociation. The synchronized improvement in photovoltage and photocurrent leads to an inverted CH3NH3PbI2.85Br0.15 planar PVSC device with power conversion efficiency of 13.7%. The spectral response characterization, time resolved photoluminescence, and transient photovoltage decay measurements highlight the efficient and simple method for perovskite devices.

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Colloidal semiconductor nanowires are interesting materials with polarized optical feature for optoelectronics devices. Previously, we observed an interesting photoluminescence enhancement in colloidal alloyed CdSe x S 1−x nanowires. In the present work, low temperature steady-state and time-resolved photoluminescence spectra were applied to understand the photoluminescence enhancement in these CdSe x S 1−x alloyed nanowires. The band-edge emission and surface-defect emission of alloyed CdSe x S 1−x nanowires, observed in low temperature photoluminescence spectra, show different changing trend with the variation of their composition. Moreover, the radiative lifetime for band-edge emission and surface-defect emission reveals an opposite changing trend with the variation of temperature. These findings suggest that the variation of photoluminescence quantum yields with composition is determined by the competition between exciton move and localization. If the carriers are localized in the interior of nanowires, the migration of photoinduced excitons to their surface will be prohibited, and more probability for radiative recombination at band edge occurred.

as well as seminar participants at various institutions for their comments. Chen acknowledges financial support from the University of Hong Kong and from Hong Kong General Research Fund (project code: 17507916), and Steinwender acknowledges financial support from McKinsey & Co. for acquiring the data. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peerreviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.