Lead halide perovskites show excellent optoelectronic properties but are unsatisfactory in terms of stability and toxicity. Herein, bismuth (Bi)‐doped lead‐free inorganic perovskites Cs2SnCl6:Bi are reported as blue emissive phosphors. Upon Bi doping, the originally nonluminous Cs2SnCl6 exhibits a highly efficient deep‐blue emission at 455 nm, with a Stokes shift of 106 nm and a high photoluminescence quantum yield (PLQY) close to 80%. Hybrid density functional theory calculations suggest the preferred formation of [BiSn+VCl] defect complex, which is believed to be responsible for the optical absorption and the associated blue emission. The Cs2SnCl6:Bi also shows impressive thermal and water stability due to its inorganic nature and the formation of protective BiOCl layer. White light‐emitting diodes (LEDs) are constructed using Cs2SnCl6:Bi and commercial yellow phosphors combined with commercial UV LED chips, giving the Commission Internationale de I'Eclairage (CIE) color coordinates of (0.36, 0.37). This work represents a significant step toward the realization of highly efficient, stable, and environmentally benign next‐generation solid‐state lighting.

Circularly polarized light (CPL) detection is required in various fields such as drug screening, security surveillance and quantum optics. Conventionally, CPL photodetector needs the installation of optical elements, imposing difficulties for integrated and flexible devices. The established CPL detectors without optical elements rely on chiral organic semiconductor and metal metamaterials, but they suffer from extremely low responsivity. Organic-inorganic hybrid materials combine CPL-sensitive absorption induced by chiral organics and efficient charge transport of inorganic frameworks, providing an option for direct CPL detection. Here we report the CPL detector using chiral organic-inorganic hybrid perovskites, and obtain a device with responsivity of 797 mA W -1 , detectivity of 7.1 × 10 11 Jones, 3-dB frequency of 150 Hz and one-month stability, a competitive combined feature for circularly polarized light detection. Thanks to the solution processing, we further demonstrate flexible devices on polyethylene terephthalate substrate with comparable performance.

Lead halide perovskite quantum dots (QDs) are promising candidates for future lighting applications, due to their high quantum yield, narrow full width at half maximum (FWHM), and wide color gamut. However, the toxicity of lead represents a potential obstacle to their utilization. Although tin(II) has been used to replace lead in films and QDs, the high intrinsic defect density and oxidation vulnerability typically leads to unsatisfactory material properties. Bismuth, with much lower toxicity than lead, is promising to constitute lead-free perovskite materials because Bi is isoelectronic to Pb and more stable than Sn . Herein we report, for the first time, the synthesis and optical characterization of MA Bi Br perovskite QDs with photoluminescence quantum yield (PLQY) up to 12 %, which is much higher than Sn-based perovskite nanocrystals. Furthermore, the photoluminescence (PL) peaks of MA Bi X QDs could be easily tuned from 360 to 540 nm through anion exchange.

and thus abundant PL emissions covering ultraviolet, visible light, as well as infrared region. [11,12] In addition, the FWHM could even reach 10 nm, enabling high color purity and serving as phosphors in display, biolabeling, etc. [13,14] Recently, some reports demonstrated that colloidal CsPbX 3 NCs with Mn 2+ doping exhibited dual-color emission, validating the facile doping in perovskites due to their nonrigid structures. [15][16][17] Manganese (Mn) ions were incorporated into CsPbX 3 NCs, exhibiting a dramatic effect on relative intensities of intrinsic band-edge emission and Mn ion emission, which was ascribed to the influence of energy transfer between the Mn ion and the semiconductor host. Subsequently, Sn 2+ , Cd 2+ , and Zn 2+ are found to partially replace Pb 2+ cations in colloidal CsPbBr 3 NCs by the method of cation exchange and lead to a blueshift of the optical spectra, while maintaining the high photoluminescence quantum yields (>50%) and narrow emission of the parent NCs. [18] However, as far as we are concerned, there is still no report about RE ion doping in lead halide perovskite NCs.In the present work, we successfully doped the RE ions Eu 3+ and Tb 3+ into CsPbBr 3 NCs through one-pot ultrasonication. The ultrasonic method has been proven a successful route for nanocrystal synthesis. [19][20][21] During the ultrasonication, acoustic cavitation could create bubbles, with the temperature of hot spots reaching above 5000 K and the pressure exceeding 1000 bar, and hence accumulate intensive energy inside. [22] Collapse of these bubbles supplies a transient ultrahigh energy to overcome the nucleation barrier and initiates the growth of NCs simultaneously. [23] Here, we believe that the ultrasonication could not only provide energy for the synthesis of our CsPbBr 3 NCs, but also facilitate the incorporation of RE dopants into the NC lattices. We thus developed a one-pot strategy to synthesize RE ion-doped halide perovskite NCs, and the synthetic process is schematically shown in Figure 1. Briefly, CsBr and PbBr 2 powder was loaded into N,N-Dimethylformamide (DMF) solution containing a proper amount of RE ions, and then the solution was subjected to ultrasonication with the assistance of water cooling. RE ion-doped CsPbBr 3 NCs were collected after centrifugation and other processes. The detailed procedure was documented in the Experimental Section. Such method has a relatively low yield (around 4.32%), and we can always find the undissolved precursors (CsBr, PbBr 2 ) in the bottom. These undissolved precursors can be reused for another sonication cycle to enable high utilization efficiency.The products were first characterized by transmission electron microscope (TEM) images, as shown in Figure 2a-c. The nondoped and doped NCs exhibited cubic shapes with different levels of aggregate and slight truncations caused by the ultrasonication synthesis procedure. The average sizes of CsPbBr 3 , CsPbBr 3 :Eu 3+ ,

Lead halide perovskite quantum dots (QDs) are promising candidates for future lighting applications,d ue to their high quantum yield, narrow full width at half maximum (FWHM), and wide color gamut. However,the toxicity of lead represents ap otential obstacle to their utilization. Although tin(II) has been used to replace lead in films and QDs,the high intrinsic defect density and oxidation vulnerability typically leads to unsatisfactory material properties.Bismuth, with much lower toxicity than lead, is promising to constitute lead-free perovskite materials because Bi 3+ is isoelectronic to Pb 2+ and more stable than Sn 2+ .Herein we report, for the first time,the synthesis and optical characterization of MA 3 Bi 2 Br 9 perovskite QDs with photoluminescence quantum yield (PLQY) up to 12 %, whichi sm uchh igher than Sn-based perovskite nanocrystals.F urthermore,t he photoluminescence (PL) peaks of MA 3 Bi 2 X 9 QDs could be easily tuned from 360 to 540 nm through anion exchange.

Lead halide perovskite nanocrystals (NCs) have attracted intense attention because of their excellent optoelectronic properties. The ionic nature of halide perovskites makes them highly vulnerable to water. Encapsulation of perovskite NCs with inorganic or organic materials has been reported to enhance their stability; however, they often suffer from large aggregation size, low water solubility, and difficulty for further surface functionalization. Here, we report a facile aqueous process to synthesize water-soluble CsPbBr 3 /Cs 4 PbBr 6 NCs with the assistance of a fluorocarbon agent (FCA), which features a novel mechanism of the perovskite crystallization at the oil/water interface and direct perovskite NCs/FCA self-assembly in an aqueous environment. The products exhibit a high absolute photoluminescence quantum yield (PLQY) of ∼80% in water with the PL lasting for weeks. Through successive ionic layer adsorption and reaction, BaSO 4 was further applied to encapsulate the NCs, which greatly enhanced their stability in phosphate-buffered saline solutions. The high stability in water and saline solution, high PLQY, and tunable emission wavelength, together with the successful demonstration of brain tissue labeling and PL under X-ray excitation, make our perovskite NCs a promising choice for X-ray fluorescent biolabels.

MapReduce is an important programming model for building data centers containing ten of thousands of nodes. In a practical data center of that scale, it is a common case that I/Obound jobs and CPU-bound jobs, which demand different resources, run simultaneously in the same cluster. In the MapReduce framework, parallelization of these two kinds of job has not been concerned. In this paper, we give a new view of the MapReduce model, and classify the MapReduce workloads into three categories based on their CPU and I/O utilization. With workload classification, we design a new dynamic MapReduce workload predict mechanism, MR-Predict, which detects the workload type on the fly. We propose a Triple-Queue Scheduler based on the MR-Predict mechanism. The Triple-Queue scheduler could improve the usage of both CPU and disk I/O resources under heterogeneous workloads. And it could improve the Hadoop throughput by about 30% under heterogeneous workloads.

No abstract