Lei Wang,Shuai Zhang,Long Yan,Xiaohong Ji,Qinyuan Zhang
The electronic and optical properties of two-dimensional transition metal dichalcogenides can be tuned by a doping strategy. Herein, spiral and monolayer Er-doped WS2 (WE) flakes have been synthesized by chemical vapor deposition using ErCl3, WO3, and S as precursors. The growth and properties of WE flakes have been systematically studied based on experimental and theoretical analysis. The morphology, size, and thickness of WE flakes can be regulated by adjusting the molar ratio of ErCl3/WO3 and the growth time. It has been found that the ErCl3 precursor not only acts as the promoter of the WE flakes during the growth but also drives the formation of screw dislocations owing to the internal strain in the lattice induced by Er3+ doping. The WE flakes exhibit near-infrared (NIR) emission at ∼1530 nm under 980 nm excitation, which corresponds to the energy transition from 4I13/2 to 4I15/2 of the Er3+ dopants. In addition, the WE-based device exhibits improved NIR photoresponse with a 16.9-fold enhancement in photocurrent compared with that of the WS2-based device. Our work provides a simple method for the preparation of highly crystalline WE flakes with NIR emission and enhanced NIR photoresponse.
Chuying Wang,Ya-Kun Wang,Ziliang Li,Jingwei Luo,Randy Sabatini,Tao Zhang,Edward H. Sargent,Zhengtao Deng
Recently, metal halide perovskites have attracted considerable interest as highly emissive phosphors for use in white light-emitting diodes (WLEDs). In perovskites, the migration of halide anions between green-emitting bromide (e.g., CsPbBr 3 ) and red-emitting iodide (e.g., CsPbI 3 ) materials is one obstacle to application. Here perovskite WLEDs that do not suffer from the anion exchange problem are reported: this is done by developing green-emitting single-layer sheets of (RNH 3 ) 2 PbI 4 (R = C 18 H 35 –, C 12 H 25 –, and C 8 H 17 –) and uniting these with red-emitting CsPbI 3 perovskite quantum dots (QDs). It relies on self-assembly from ligand-capped CsPbI 3 nanocrystals to form single-layer sheets of (C 18 H 35 NH 3 ) 2 PbI 4 : via judicious selection of alkylamines and alkyl acids, (RNH 3 ) 2 PbI 4 single-layer sheets that exhibit bright and stable green emission with well-defined single-layer thickness are produced. Emission from 505, 512 to 536 nm is tuned and a narrow (<20 nm) linewidth is retained. Perovskite LEDs that produce white light with chromaticity coordinates (0.32, 0.33) and color gamut that reaches 117% National Television System Committee (NTSC) in the International Commission on Illumination (CIE) 1931 color space are demonstrated.
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