Semiconductor quantum dots (QDs) with stable, oxidation resistant, and tunable photoluminescence (PL) are highly desired for various applications including solid-state lighting and biological ...labeling. However, many current systems for visible light emission involve the use of toxic Cd. Here, we report the synthesis and characterization of a series of codoped core/shell ZnSe/ZnS QDs with tunable PL maxima spanning 430−570 nm (average full width at half-maximum of 80 nm) and broad emission extending to 700 nm, through the use of Cu+ as the primary dopant and trivalent cations (Al3+, Ga3+, and In3+) as codopants. Furthermore, we developed a unique thiol-based bidentate ligand that significantly improved PL intensity, long-term stability, and resilience to postsynthetic processing. Through comprehensive experimental and computational studies based on steady-state and time-resolved spectroscopy, electron microscopy, and density functional theory (DFT), we show that the tunable PL of this system is the result of energy level modification to donor and/or acceptor recombination pathways. By incorporating these findings with local structure information obtained from extended X-ray absorption fine structure (EXAFS) studies, we generate a complete energetic model accounting for the photophysical processes in these unique QDs. With the understanding of optical, structural, and electronic properties we gain in this study, this successful codoping strategy may be applied to other QD or related systems to tune the optical properties of semiconductors while maintaining low toxicity.
Design of metal–semiconductor interfaces and heterostructures is of strong interest for various catalytic applications including photocatalysis. In this work, a series of hollow Au nanosphere ...(HGN)–Cu2O core–shell nanostructures with varying core surface rugosities are synthesized and investigated for possible photocatalytic applications. HGN surface rugosity is tuned by pH modification during galvanic exchange, and carboxyl groups are utilized as coordination sites to deposit uniform Cu2O shells onto the gold surfaces. Final core–shell structures are verified by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). Information regarding chemical state and electronic band structure is acquired by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). Ultrafast transient absorption (TA) reveals that charge separation in bumpy HGN (bHGN)–Cu2O may effectively provide longer-lived photoexcited carriers, offering great potential for utilization in advanced photocatalytic processes.
The combination of hollow core and rugose surface morphology is highly attractive for photoactive near-infrared (NIR) nanomaterials. Here, we present a facile pH modification to hollow gold ...nanosphere (HGN) synthesis to enable controlled tuning of the surface morphology from smooth to very bumpy. Unlike other methods, the synthetic protocol does not require harsh surfactants, secondary reducing agents, or organic solvents. The resultant bumpy HGNs (bHGNs) are highly monodisperse with little variation in protrusion length from particle to particle. Mechanistic studies suggest that surface rugosity is mainly controlled by the presence of free OH– ions in solution. We also present the first systematic investigation into the effect of surface morphology on the photothermal conversion efficiency (PCE) of bumpy as well as smooth HGNs, with a maximum PCE reaching 99%. Although expected to have a higher scattering component, the bHGNs retain the excellent PCE of their smooth counterparts, which may be due to efficient reabsorption of scattered light.
Lyme disease (LD) is the most common vector-borne disease in the United States, with increasing incidence and geographic range. Case incidence peaks among school-aged children. New LD preventives are ...in clinical trials.
We conducted an online survey of parents of children aged 5–18 years in states with high or emerging incidence of LD. Our primary outcome was willingness (“definitely” or “probably”) for their child to receive an LD vaccine. Our secondary outcome was preference for annual monoclonal antibody injections compared to a 3-dose vaccine series with boosters. Analyses were weighted to reflect parent gender, parent race/ethnicity, and child age by state.
Among 1,351 parent respondents, most (68.0 %) would have their child vaccinated against LD, with significantly more being willing in high compared to emerging incidence states (70.4 % versus 63.6 %, p = 0.027). Of parents who were unsure or unwilling, 33.5 % and 16.5 %, respectively, would do so with a provider recommendation. Vaccine safety concerns were among the top reasons for LD vaccine hesitancy. More parents preferred a pre-formed antibody (42.3 %) compared to a 3-dose vaccine series (34.7 %). Significant predictors of willingness to have one’s child vaccinated were higher parental education; higher perceived risk of child getting LD; child spending time outdoors daily or weekly; following a regular vaccine schedule; and positive attitude towards vaccines. Significant predictors of preference for monoclonal antibody over a 3-dose vaccine series included prior awareness of LD, living in a rural area, and less positive attitudes towards vaccines.
Two-thirds of parents in high and emerging incidence states would vaccinate their children against Lyme disease. Addressing safety concerns will be important, and a health care provider recommendation could also encourage those who are unsure or unwilling. Given the slight preference for monoclonal antibody over vaccine, particularly in rural areas, access to both may increase LD prevention.
Assessing the intrinsic material performance of emerging copper-based ternary oxide photocathode candidate materials such as CuBi2O4 (CBO) has been challenging due to the formation of ...phase-segregated domains in films with stoichiometric nonideality. However, we find films with CuO phase segregation demonstrate improved photoelectrochemical (PEC) performance, the origin of which inspired this deeper investigation. Uniform and compact CBO thin films with Bi:Cu ratios of 2.10, 1.97, 1.78, and 1.38 were grown by spin-coating. Although CuO was detected by Raman and X-ray diffraction in the 1.38 film only, high resolution energy-dispersive X-ray spectroscopy mapping revealed the presence of 10–20 nm CuO particles at the CBO/FTO interface in the 1.38, 1.78, and 1.97 samples. The greater number of CuO particles in the 1.38 sample resulted in a 25% enhancement in incident photon-to-current efficiency performance but could not be attributed to CuO-related light absorption. X-ray photoelectron spectroscopy characterization of the type-II band alignment was used to confirm that the particles behave as hole-selective contacts. The presence of nanoparticulate heterojunctions improves carrier collection of low diffusion length holes, enhancing the performance of the heterojunction beyond that of a fully planar derivative.
Hollow gold nanospheres (HGNs) have been used as the template for seed-mediated growth of multibranched hollow gold nanostars (HNS). The HGNs were synthesized via anerobic reduction of cobalt ...chloride to cobalt nanoparticles and then formation of a gold shell via galvanic replacement followed by the oxidation of the cobalt core. We obtained control of the inner core size of the HGNs by increasing the size of the sacrificial cobalt core and by varying the ratio of B(OH)3/BH4 using boric acid rather than 48 h aged borohydride. We synthesized the HNS by reducing Au3+ ions in the presence of Ag+ ions using ascorbic acid, creating a spiky morphology that varied with the Au3+/Ag+ ratio. A broadly tunable localized surface plasmon resonance was achieved through control of both the inner core and the spike length. Amyloid beta (Aβ) was conjugated to the HNS by using a heterobifunctional PEG linker and identified by the vibrational modes associated with the conjugated ring phenylalanine side chain. A bicinchoninic acid assay was used to determine the concentration of Aβ conjugated to HNS as 20 nM, which is below the level of Aβ that negatively affects long-term potentiation. Both the core size and spike length were shown to affect the optical properties of the resulting nanostructures. This HGN templated method introduced a new parameter for enhancing the plasmonic properties of gold nanostars, namely, the addition of a hollow core. Hollow gold nanostars are highly desirable for a wide range of applications, including high sensitivity disease detection and monitoring.
We present the fabrication and characterization of Ti-doped hematite ( alpha -Fe sub(2)O sub(3)) films for application as photoanodes in photoelectrochemical (PEC) cells for water splitting. It is ...demonstrated that Ti doping significantly improves the PEC activity as the photocurrent at 1.0 V vs.Ag/AgCl electrode for a 400 nm thick Ti-doped film (0.66 mA cm super(-2)) was found to be similar to 14 times higher than that of an undoped film (0.045 mA cm super(-2)). The films were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and ultrafast transient absorption spectroscopy to obtain information about their structural, electronic, and charge carrier dynamic properties. Based on characterization of the chemical states of the involved elements as well as the charge carrier dynamics of the films with Ti doping, it appears that the photocurrent enhancement is related to an increase in charge carrier density or reduced electron-hole recombination. The highest incident photon conversion efficiency (IPCE) measured for this system was 27.0% at 360 nm at a potential of 1.23 V vs.reversible hydrogen electrode (RHE), which was obtained on a 400 nm thick Ti-doped alpha -Fe sub(2)O sub(3) film.
In principle, the diameter and surface plasmon resonance (SPR) frequency of hollow metal nanostructures can be independently adjusted, allowing the formation of targeted photoactivated structures of ...specific size and optical functionality. Although tunable SPRs have been reported for various systems, the shift in SPR is usually concomitant with a change in particle size. As such, more advanced tunability, including constant diameter with varying SPR or constant SPR with varying diameter, has not been properly achieved experimentally. Herein, we demonstrate this advanced tunability with hollow gold nanospheres (HGNs). HGNs were synthesized through galvanic exchange using cobalt-based nanoparticles (NPs) as sacrificial scaffolds. Co2B NP scaffolds were prepared by sodium borohydride nucleation of aqueous cobalt chloride and characterized using UV–vis, dynamic light scattering, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Careful control over the size of the Co2B scaffold and its galvanic conversion is essential to realize fine control of the resultant HGN diameter and shell thickness. In pursuit of size control, we introduce B(OH)4 – (the final product of NaBH4 hydrolysis) as a growth agent to obtain hydrodynamic diameters ranging from ∼17–85 nm with relative standard deviation <3%. The highly monodisperse Co2B NPs were then used as scaffolds for the formation of HGNs. In controlling HGN shell thickness and uniformity, environmental oxygen was shown to affect both the structural and optical properties of the resultant gold shells. With careful control of these key factors, we demonstrate an HGN synthesis that enables independent variation of diameter and shell thickness, and thereby SPR, with unprecedented uniformity. The new synthesis method creates a truly tunable plasmonic nanostructure platform highly desirable for a wide range of applications, including sensing, catalysis, and photothermal therapy.
Charge transport mediators are commonly used in photoelectronic devices to promote selective charge transport and mitigate carrier losses. However, related investigations are mainly carried out by ...the trial‐and‐error method, and a deeper understanding of its local charge transport behavior is still lacking. Herein, a comprehensive study is performed on a BiVO4/Ti3C2 photoanode to reveal its local charge transport properties by combing microprobe technologies and numerical computations. For the first time, a nano‐Schottky junction is directly shown at the BiVO4/Ti3C2 interface and the band bending is quantified with promoted hole transport and prolonged photocarrier's lifetime. These mechanistic insights leverage a path to further optimize performance through interface engineering and achieve a photocurrent of 5.38 mA cm−2 at 1.23 V versus reversible hydrogen electrode. This work provides deeper insight into the function of charge transport mediators in view of interface contact rather than material nature and demonstrates a strategy to improve photoelectrochemical performance through Fermi‐level engineering.
Local photocurrent imaging analysis provides a deeper understanding of interfacial charge transport behavior at the nanoscale, which facilitates the development and optimization of charge select materials for the photoelectrochemical system to efficient solar fuel production.
In this study, we report anomalous size-dependent photoluminescence (PL) intensity variation of PbS quantum dots (QDs) with the formation of a thin CdS shell via a microwave-assisted cation exchange ...approach. Thin shell formation has been established as an effective strategy for increasing the PL of QDs. Nonetheless, herein we observed an unusual PL decrease in ultrasmall QDs upon shell formation. We attempted to understand this abnormal phenomenon from the perspective of trap density variation and the probability of electrons and holes reaching surface defects. To this end, the quantum yield (QY) and PL lifetime (on the ns-μs time scales) of pristine PbS QDs and PbS/CdS core/shell QDs were measured and the radiative and non-radiative recombination rates were derived and compared. Moreover, transient absorption (TA) analysis (on the fs-ns time scale) was performed to better understand exciton dynamics at early times that lead to and affect longer time dynamics and optical properties such as PL. These experimental results, in conjunction with theoretical calculations of electron and hole wave functions, provide a complete picture of the photophysics governing the core/shell system. A model was proposed to explain the size-dependent optical and dynamic properties observed.
PDF
