Phosphorescent sensor for biological mobile zinc

A new phosphorescent zinc sensor (ZIrF) was constructed, based on an Ir(III) complex bearing two 2-(2,4-difluorophenyl)pyridine (dfppy) cyclometalating ligands and a neutral 1,10-phenanthroline (phen) ligand. A zinc-specific di(2-picolyl)amine (DPA) receptor was introduced at the 4-position of the phen ligand via a methylene linker. The cationic Ir(III) complex exhibited dual phosphorescence bands in CH[subscript 3]CN solutions originating from blue and yellow emission of the dfppy and phen ligands, respectively. Zinc coordination selectively enhanced the latter, affording a phosphorescence ratiometric response. Electrochemical techniques, quantum chemical calculations, and steady-state and femtosecond spectroscopy were employed to establish a photophysical mechanism for this phosphorescence response. The studies revealed that zinc coordination perturbs nonemissive processes of photoinduced electron transfer and intraligand charge-transfer transition occurring between DPA and phen. ZIrF can detect zinc ions in a reversible and selective manner in buffered solution (pH 7.0, 25 mM PIPES) with K[subscript d] = 11 nM and pK[subscript a] = 4.16. Enhanced signal-to-noise ratios were achieved by time-gated acquisition of long-lived phosphorescence signals. The sensor was applied to image biological free zinc ions in live A549 cells by confocal laser scanning microscopy. A fluorescence lifetime imaging microscope detected an increase in photoluminescence lifetime for zinc-treated A549 cells as compared to controls. ZIrF is the first successful phosphorescent sensor that detects zinc ions in biological samples.National Institute of General Medical Sciences (U.S.) (Grant GM065519)Ewha Woman's University (Korea) (RP-Grant 2010

Photoluminescence of hollow gold-silver bimetallic nanoparticles

Hollow gold nanoparticles including silver were prepared by the galvanic replacement reaction of silver nanoparticles by gold. The resulting hollow gold-silver bimetallic nanoparticles show notable blue-green emissions, which are studied using steady-state and time-resolved spectroscopy

Antisolvent-assisted one-step solution synthesis of defect-less 1D MAPbI3 nanowire networks with improved charge transport dynamics

In this study, both one-dimensional (1D) and three-dimensional (3D) methylammonium lead iodide (MAPbI3) were successfully synthesized from the same starting precursor solution using a one-step in situ spin-coating process assisted by antisolvent washing with different ethereal solvents. Antisolvent washing with diethyl ether (DE) induced isotropic growth, resulting in dense 3D MAPbI3 films. However, washing with dibutyl ether (DB) having complementary properties promoted 1D directional growth to avoid steric hindrance in the DB/perovskite complex. Antisolvent DB having a lower vapor pressure than DE retarded the vaporization of dimethylformamide and facilitated the growth of larger grains with fewer defects through the slow crystallization. It was also found that long-chain induced 1D directional growth creates an internal compressive strain in the 1D NW film, which plays an important role in charge carrier dynamics. To compare the power conversion efficiency (PCE) and charge transport dynamics, planar solar cells based on both 1D and 3D perovskites were fabricated. 1D NW perovskite based devices achieved a longer lifetime and faster carrier transport owing to the limited ion migration in the presence of compressive strain, although the PCE (15.73%) of the 1D NW-based device was lower than that (18.73%) of the 3D bulk-based device due to inevitable pore incorporation. The improved charge carrier dynamics of 1D NW MAPbI3 can offer potential advantages in the development of optoelectronic devices

Multiple-Route Exciton Recombination Dynamics and Improved Stability of Perovskite Quantum Dots by Plasmonic Photonic Crystal

We have studied the excited-state exciton recombination dynamics of perovskite quantum dots (QDs) through time-resolved photoluminescence (PL), PL blinking, PL intensity-dependent lifetime modulation, and long-term photostability tests. The various spectroscopic characterizations elucidate that the perovskite QDs have multiple intrinsic exciton recombination routes even in a single QD, i.e., exciton, biexciton, and positive/negative trions, which are dissimilarly contributed to ON and OFF state emissions. We also find that the enhanced radiative recombination from placing green QDs on a photonic Ag nanotip array induces notably improved long-term PL stability. We consider that the accelerated radiative recombination of QDs by strong coupling with the plasmonics of the photonic Ag nanotip array, while eliminating nonradiative pathways, is proven to be a critical factor for improved long-term stability. © 2022 American Chemical Society.FALS

Magnetron Sputtered Al Co-Doped with Zr-Fe₂O₃ Photoanode with Fortuitous Al₂O₃ Passivation Layer to Lower the Onset Potential for Photoelectrochemical Solar Water Splitting

In this paper, we investigate the magnetron sputtering deposition of an Al-layer on Zr-doped FeOOH (Zr-FeOOH) samples to fabricate a Zr/Al co-doped Fe2O3 (Al-Zr/HT) photoanode. An Al-layer is deposited onto Zr-FeOOH through magnetron sputtering and the thickness of the Al deposition is regulated by differing the sputtering time. Electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, Mott-Schottky and time-resolved photoluminescence spectra analyses were used to study, in depth, the correlations between sputtered Al-layer thicknesses and PEC characteristics. High-temperature quenching (800 °C) assists in diffusing the Al3+ in the bulk of the Zr-doped Fe2O3 photoanode, whilst an unintended Al2O3 passivation layer forms on the surface. The optimized Al-Zr/HT photoelectrode achieved 0.945 mA/cm2 at 1.0 VRHE, which is 3-fold higher than that of the bare Zr/HT photoanode. The Al2O3 passivation layer causes a 100 mV cathodic shift in the onset potential. Al co-doping improved the donor density, thus reducing the electron transit time. In addition, the passivation effect of the Al2O3 layer ameliorated the surface charge transfer kinetics. The Al2O3 passivation layer suppressed the surface charge transfer resistance, consequently expediting the hole migration from photoanode to electrolyte. We believe that the thickness-controlled Al-layer sputtering approach could be applicable for various metal oxide photoanodes to lower the onset potential

Importance of Surface Functionalization and Purification for Narrow FWHM and Bright Green-Emitting InP CoreMultishell Quantum Dots via a Two-Step Growth Process

Indium phosphide (InP)-based quantum dots (QDs) are widely studied as environmentally friendly light emitters for display applications. However, the synthesis of InP QDs with optical properties that meet high color quality as comparable with cadmium (Cd)- and lead (Pb)-based QDs is challenging. In this article, we present the synthesis of surface-modified bright green luminescence InP core-shell quantum dots (CS-QDs) with the narrowest full width at half-maximum (fwhm) of 33 nm, absolute quantum yield (QY) of 71%, and an absorption spectra valley/depth (V/D) ratio of 0.61 after a size selection purification process. Our approach first emphasizes the heating temperatures for InP growth and second on the importance of surface stabilization of this system. We developed a two-step heating-up process to grow In(Zn)P core and coated inorganic shell with ZnSe/ZnSeS/ZnS composition. In situ surface treatment with zinc chloride (ZnCl2) and 1-octanol was carried out to enhance the PLQY and improve the surface passivation of the CS-QDs. Optical spectroscopy and surface characterization techniques including nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and infrared (IR) spectroscopy were used to analyze the properties of the CS-QDs. We suggest that this work motivates future development and optimization of surface chemistry of InP CS-QDs to enable the full access and realization of their luminescence efficiency in high-color-quality cadmium (Cd)-free displays. ©1

Optical resonance and charge transfer behavior of patterned WO3 microdisc arrays

One- to three-dimensional alignments of semiconductors on the micro- or nanoscale have been achieved to tailor their opto-physicochemical properties and improve their photoelectrochemical (PEC) performance. Here, to the best of our knowledge, we report for the first time the fabrication of vertically aligned, well-ordered WO3 microdisc arrays via an electrodeposition process on lithographically patterned indium tin oxide (ITO) substrates as well as their geometry-specific photoelectrochemical properties. The as-fabricated WO3 microdisc arrays exhibit enhanced light absorption as well as facilitated charge separation, leading to significantly higher PEC performance than WO3 films. A finite-difference time-domain simulation of a single WO3 microdisc indicates that strong optical resonances occur particularly in the central part of the microdisc, leading to enhanced optical absorption. A time-resolved photoluminescence study further reveals that the average lifetime of charge carriers (τ) in a microdisc array is shorter than that in a film by ∼60%. The reductively deposited Au particles are localized on the side of the microdisc and ITO substrate, which suggests that the photogenerated electrons are transferred to the same location. In addition, the oxidative deposition of FeOOH particles on the top surface and side of a microdisc indicates hole transfer pathways at the same location. This downward transfer of electrons and upward transfer of holes lead to efficient charge separation, and the radial direction appears to be the most preferred shortcut for the carriers inside the bulk of a microdisc. © 2016 The Royal Society of Chemistry.1

Photoelectrochemical hydrogen production on silicon microwire arrays overlaid with ultrathin titanium nitride

p-Si wire arrays overlaid with an ultrathin titanium nitride (TiN) film are developed and demonstrated to be an efficient and robust photocathode for hydrogen production. Arrays of vertically aligned 20 μm long p-Si microwires of varying diameters (1.6-14.6 μm) are fabricated via a photolithographic technique, and then the wires are coated with a TiN nanolayer 2-20 nm thick by low-temperature plasma-enhanced atomic layer deposition. The optimized heterojunction consisting of 1.6 μm-thick wires covered by 10 nm thick TiN exhibits significantly improved performance for hydrogen evolution reaction under simulated sunlight (AM 1.5G, 100 mW cm-2). It displays a photocurrent onset potential of ∼+0.4 V vs. reversible hydrogen electrode (RHE), and a faradaic efficiency of nearly 100% at 0 V vs. RHE over 20 h of reaction. Time-resolved photoluminescence decay reveals that the lifetime (τ) of the photogenerated charge carriers in the optimized wire/TiN heterojunction is ∼60% shorter than those using thicker wires, suggesting significantly faster charge transfer. Such remarkable performance is attributed to enhanced transfer of the minority carriers in the radial direction of the wires. TiN performs the triple roles of antireflection, protection of the Si surface, and electrocatalysis of hydrogen production. Finite-difference time-domain simulation reveals a significant increase in the absorptance of wire arrays with TiN film, and that long wavelength photons are more effectively absorbed by the wire/TiN arrays. © 2016 The Royal Society of Chemistry.

Excitation dynamics of MAPb(I1-xBrx)(3) during phase separation by photoirradiation: Evidence of sink, band filling, and Br-Rich phase coarsening

Here, we report the radiative recombination behavior of a binary perovskite, MAPb(I0.2Br0.8)3, during phase separation by investigating photoluminescence (PL) spectrum modulations under different laser irradiation conditions: power density, wavelength (379 and 470 nm), and irradiation time. During laser irradiation, the original PL spectrum was divided into three PL peaks assigned to the 1st I-rich, 2nd I-rich, and Br-rich phases. The observed modulations of the intensity and wavelength of the PL spectrum could be explained by the multiple effects of the charge carrier sink, band filling, and Br-rich phase coarsening. Under a weak laser power density, the observed PL predominantly showed the sink effects of the charge carriers through the excited state potential minimum. As the laser power density or irradiation time increased, new high-energy PL bands appeared owing to the band filling and Br-rich phase formation. With a further increase in the laser power or irradiation time, the PL from the Br-rich phase was intensified, but its PL peak position was red-shifted owing to the quantum size effect from the Br-rich phase coarsening. These variations in PL intensity and charge carrier behavior were carefully studied using time- and space-resolved fluorescence imaging microscopy. © 20191