Highly sensitive and selective visual detection of Cr(VI) ions based on etching of silver-coated gold nanorods

We report a visual detection of Cr(VI) ions using silver-coated gold nanorods (AuNR@Ag) as sensing probes. Au NRs were prepared by a seed-mediated growth process and AuNR@Ag nanostructures were synthesized by growing Ag nanoshells on Au NRs. Successful coating of Ag nanoshells on the surface of Au NRs was demonstrated with TEM, EDS, and UV–vis spectrometer. By increasing the overall amount of the deposited Ag on Au NRs, the localized surface plasmon resonance (LSPR) band was significantly blue-shifted, which allowed tuning across the visible spectrum. The sensing mechanism relies on the redox reaction between Cr(VI) ions and Ag nanoshells on Au NRs. As the concentration of Cr(VI) ions increased, more significant red-shift of the longitudinal peak and intensity decrease of the transverse peak could be observed using UV–vis spectrometer. Several parameters such as concentration of CTAB, thickness of the Ag nanoshells and pH of the sample were carefully optimized to determine Cr(VI) ions. Under optimized condition, this method showed a low detection limit of 0.4 μM and high selectivity towards Cr(VI) over other metal ions, and the detection range of Cr(VI) was tuned by controlling thickness of the Ag nanoshells. From multiple evaluations in real sample, it is clear that this method is a promising Cr(VI) ion colorimetric sensor with rapid, sensitive, and selective sensing ability.This research was supported under the framework of Nano Material Technology Development Program (NRF-2015M3A7B6027970) and Basic Science Research Program (NRF-2018R1D1A1B07051249) by National Research Foundation, South Korea. Also, this work was supported by the Center of Integrated Smart Sensors funded by the Ministry of Science, ICT and Future Planning, South Korea, as Global Frontier Project (CISS-012M3A6A6054186

Synergistic surface modification for high-efficiency perovskite nanocrystal light-emitting diodes: divalent metal ion doping and halide-based ligand passivation

Surface defects of metal halide perovskite nanocrystals (PNCs) substantially compromise the optoelectronic performances of the materials and devices via undesired charge recombination. However, those defects, mainly the vacancies, are structurally entangled with each other in the PNC lattice, necessitating a delicately designed strategy for effective passivation. Here, a synergistic metal ion doping and surface ligand exchange strategy is proposed to passivate the surface defects of CsPbBr3 PNCs with various divalent metal (e.g., Cd2+, Zn2+, and Hg2+) acetate salts and didodecyldimethylammonium (DDA+) via one-step post-treatment. The addition of metal acetate salts to PNCs is demonstrated to suppress the defect formation energy effectively via the ab initio calculations. The developed PNCs not only have near-unity photoluminescence quantum yield and excellent stability but also show luminance of 1175 cd m−2, current efficiency of 65.48 cd A−1, external quantum efficiency of 20.79%, wavelength of 514 nm in optimized PNC light-emitting diodes with Cd2+ passivator and DDA ligand. The “organic–inorganic” hybrid engineering approach is completely general and can be straightforwardly applied to any combination of quaternary ammonium ligands and source of metal, which will be useful in PNC-based optoelectronic devices such as solar cells, photodetectors, and transistors

Synergistic Surface Modification for High‐Efficiency Perovskite Nanocrystal Light‐Emitting Diodes: Divalent Metal Ion Doping and Halide‐Based Ligand Passivation

Abstract Surface defects of metal halide perovskite nanocrystals (PNCs) substantially compromise the optoelectronic performances of the materials and devices via undesired charge recombination. However, those defects, mainly the vacancies, are structurally entangled with each other in the PNC lattice, necessitating a delicately designed strategy for effective passivation. Here, a synergistic metal ion doping and surface ligand exchange strategy is proposed to passivate the surface defects of CsPbBr3 PNCs with various divalent metal (e.g., Cd2+, Zn2+, and Hg2+) acetate salts and didodecyldimethylammonium (DDA+) via one‐step post‐treatment. The addition of metal acetate salts to PNCs is demonstrated to suppress the defect formation energy effectively via the ab initio calculations. The developed PNCs not only have near‐unity photoluminescence quantum yield and excellent stability but also show luminance of 1175 cd m−2, current efficiency of 65.48 cd A−1, external quantum efficiency of 20.79%, wavelength of 514 nm in optimized PNC light‐emitting diodes with Cd2+ passivator and DDA ligand. The “organic–inorganic” hybrid engineering approach is completely general and can be straightforwardly applied to any combination of quaternary ammonium ligands and source of metal, which will be useful in PNC‐based optoelectronic devices such as solar cells, photodetectors, and transistors

Multicolor, dual-image, printed electrochromic displays based on tandem configuration

We prepared multicolor, dual-image, printed electrochromic displays (ECDs) based on three hybrid electrodes containing mesoporous titanium dioxide (TiO2) functionalized with various phosphonated viologens. When the hybrid electrodes are employed in ECDs, diverse colors (e.g., cyan, green, magenta, emerald, and yellow) are obtained depending on the electron affinity of the N-substituents of the viologen. The devices show fast switching speed (e.g., avg. coloration - 2.0 s and bleaching - 1.5 s) and high coloration efficiency (avg. - 328.8 cm2/C), which is attributed to the large surface area of the hybrid electrode. We also introduced a tandem configuration by inserting double-sided fluorine-doped tin oxide electrode (dsFTO) between two hybrid electrodes to overcome the limitation of the achievable colors (one or maximum two) in a single cell. The dsFTO can serve as a counter electrode of both hybrid electrodes, allowing independent or simultaneous operation of each hybrid electrode through adjusting applied voltage. To extend the functionality of tandem ECDs, the patterned hybrid electrodes are fabricated using electrostatic-force-assisted dispensing printing and applied to ECDs. The resulting devices alternately exhibit two pieces of information in a variety of colors, in which the device operation is controllable in accordance with the direction of applied voltage and the combination of hybrid electrodes. The printed, tandem structured ECDs are expected to have high potential for next-generation transparent displays.11Nscopu