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(a) Energy band diagram of InP/ZnO/ZnS core/shell/shell QDs. Quantum mechanical simulations of (b) InP core, (c) InP/ZnO core/ shell, and (d) InP/ZnO/ZnS core/shell/shell QDs. Black lines correspond to the radial probability distribution of electrons, while red lines show the radial probability distribution of holes. Black and red dashed lines correspond to confinement potential profile for electrons and holes, respectively.
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It is a generally accepted perspective that type-II nanocrystal quantum dots (QDs) have low quantum yield due to the separation of the electron and hole wavefunctions. Recently, high quantum yield levels were reported for cadmium-based type-II QDs. Hence, the quest for finding non-toxic and efficient type-II QDs is continuing. Herein, we demonstrat...
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... Mechanical Calculations and Optical Analysis. To understand the optical properties of the synthesized QDs, we calculated their quantum mechanical properties by selfconsistently solving Poisson−Schrö dinger equations in the effective mass approximation (Figure 1b−d) and correlated them with the optical measurements ( Figure 2). 24 InP core QD has type-I band alignment that led the confinement of electrons and holes in the same spatial core region with a high overlap of the wavefunctions of ∼90% (Figure 1b). ...
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... understand the optical properties of the synthesized QDs, we calculated their quantum mechanical properties by selfconsistently solving Poisson−Schrö dinger equations in the effective mass approximation (Figure 1b−d) and correlated them with the optical measurements ( Figure 2). 24 InP core QD has type-I band alignment that led the confinement of electrons and holes in the same spatial core region with a high overlap of the wavefunctions of ∼90% (Figure 1b). After ZnO shell growth, the band alignment of the nanostructure transit from type-I to type-II, and while hole wavefunction is confined completely in the core region like in InP core QD, electron wavefunction expands toward the ZnO shell that reduces the wavefunction overlap to 60% (Figure 1c). ...
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... InP core QD has type-I band alignment that led the confinement of electrons and holes in the same spatial core region with a high overlap of the wavefunctions of ∼90% (Figure 1b). After ZnO shell growth, the band alignment of the nanostructure transit from type-I to type-II, and while hole wavefunction is confined completely in the core region like in InP core QD, electron wavefunction expands toward the ZnO shell that reduces the wavefunction overlap to 60% (Figure 1c). 34 Since the delocalization of the electron decreases the confinement energy level within the conduction band and the exciton binding energy, the photo- luminescence peak red-shifted from 585 to 613 nm, while the full width at half-maximum (fwhm) was maintained at ∼74−75 nm for core and core/shell nanostructures. ...
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... understand the size and shape of the QDs, we performed small-angle X-ray scattering (SAXS) measurements in ethanol 38 by probing up to 10 6 individual particles. The scattering data after subtracting the ethanol background are shown in Figure S1, which are plotted versus the reciprocal scattering vector q. As shown in Figure 3a, we plotted instead of the reciprocal form factor P(q) directly its Fourier transform, the pair distance distribution function (PDDF) in real space. ...
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... of the QDs within the ensemble depict long-axis values between 6 and 7 nm, which is within the broader mean size distribution found by TEM with a maximum at 7.02 ± 0.9 nm (Figure 3e). The elongated shape of the QD-4ZnS NCs together with their chainlike fractal aggregation (see Figure S1) can be explained by a slightly inhomogeneous growth of the ZnS shell, resulting in an overall prolate like NC shape. This kind of elliptical NC shape can be found also for other core/shell NC systems with thick shells, where the shell growth along specific crystallographic directions is energetically favored. ...
Citations
... Recently, Cd-free Type-II InP/ZnO/ZnS Quantum Dots-based LEDs led to the most efficient external quantum efficiency of 9.4% and a power conversion efficiency of 6.8%, respectively [222]. However, an efficient and Stable CdSe/CdS/ZnS Quantum Rods-in-Matrix Assembly-based CdSe/CdS QRs LED has been fabricated utilizing a stable ZnS encapsulation, that shows a high quantum efficiency (QE) of ∼85%, while white lightemitting diodes (WLEDs) devices depict high optical performance revealing huge potentiality of II-VI semiconductor in LEDs technology [210,211]. ...
... (a) Schematic of InP/ZnO/ZnS core/shell/shell QDs light-emitting devices with energy band diagram, and (b) PCE (%) and EQE (%) at different OD (optical densities) values. Data from Eren G O et al[222]. ...
The demand for advanced electronic and optoelectronic devices has driven significant research and development efforts toward exploring emerging semiconductor materials with enhanced performance characteristics. II-VI semiconductors have been studied extensively owing to their wide bandgap characteristics, which enable high electron mobility, excellent thermal stability, and resistance to radiation damage. These properties make them well-suited for a range of applications, including solar cells, light-emitting diodes (LEDs), photodetectors, lasers, sensors, and field effect transistors (FETs). In II-VI compounds, both ionic and covalent bonds exist with a higher electronegative nature of the VI-group elements than II-group elements. This existing ionic behavior strongly influences the binding of valence band electrons rather strongly to the lattice atoms. Thus, the II-VI semiconductors such as CdS, CdTe, ZnS, ZnSe, and CdSe possess wide tunable bandgaps (~0.02 to ≥ 4.0 eV) and high absorption coefficients of approximately 106 cm-1, setting them apart from other semiconductors formed by a covalent bond with closely equal atomic weights. This review article delves into the physics of II-VI semiconductor homo/heterojunctions, and the steps involved in device fabrication including lithography, etching, metallization, stability (oxidation and passivation) and polymerization together with several doping strategies. Furthermore, this review explores the process for tuning the distinct physical and chemical properties and a substantial advancement in electronic, and optoelectronic devices, including tools, cutting-edge equipment, and instrumentations. This comprehensive review provides detailed insights into the potential and technological progress of II-VI wide bandgap semiconductor device technology including experienced challenges and prospects.
... X-ray diffraction (XRD) analysis confirmed the cubic crystal structure of InP with the (1 1 1), (2 2 0), and (3 1 1) planes (JCPDS 32-0452) ( Fig. 1(d)). Additionally, we did not observe any separate XRD peaks of ZnO QDs, which implies that ZnO shell grew on InP core [40]. X-ray photoelectron spectroscopy (XPS) analysis was performed to confirm the elemental surface chemistry of the InP core. ...
... X-ray photoelectron spectroscopy (XPS) analysis was performed to confirm the elemental surface chemistry of the InP core. In this regard, we identified two distinct peaks at 444.48 eV (3d 5/2 ) and 452.02 eV (3d 3/2 ) that can be assigned to InP (Fig. S2(a)) [40][41][42]. Additionally, the dominant doublet at 128.22-129.11 eV (2p 3/2 ) was the characteristic peak for InP [40,43], while the doublet in the 132.58-133.47 eV range indicated P atoms in an oxidized medium (InPO X ), which is a generally observed phenomena for InP QDs (Fig. S2(b)) [40,[44][45][46]. ...
... Additionally, the dominant doublet at 128.22-129.11 eV (2p 3/2 ) was the characteristic peak for InP [40,43], while the doublet in the 132.58-133.47 eV range indicated P atoms in an oxidized medium (InPO X ), which is a generally observed phenomena for InP QDs (Fig. S2(b)) [40,[44][45][46]. To form type-II band alignment and to investigate the effect of shell thickness on optical properties of QDs, we grew multiple ZnO shells on InP core structure by using thermal decomposition of zinc acetylacetonate (see methods about the reaction details) [47,48]. ...
... The very common GaAs semiconductors (doped with Al or In) are our focus here. Other common III-V semiconductor QDs are made of InP [57,58]. Significant examples of II-VI semiconductors are CdS [11], ZnO, or ZnS [58] and even silicon-based materials [59] have been designed and created relying on the advanced silicon manufacturing technology. ...
... Other common III-V semiconductor QDs are made of InP [57,58]. Significant examples of II-VI semiconductors are CdS [11], ZnO, or ZnS [58] and even silicon-based materials [59] have been designed and created relying on the advanced silicon manufacturing technology. Finally, it should be highlighted that carbon-based structures are promising candidates that aim to provide ecologically responsible and sustainable technological applications [60,61]. ...
Inter-particle Coulombic electron capture (ICEC) is an environment-enabled electron capture process by means of which a free electron can be efficiently attached to a system (e.g. ion, atom, molecule, or quantum dot). The excess electron attachment energy is simultaneously transferred to a neighboring system which concomitantly undergoes ionization (or excitation). ICEC has been theoretically predicted in van-der-Waals and in hydrogen-bonded systems as well as in quantum dot arrays. The theoretical approaches employed in these works range from analytical models to electronic structure and (quantum) dynamical calculations. In this article, we provide a comprehensive review of the main theoretical approaches that have been developed and employed to investigate ICEC and summarize the main conclusions learned from these works. Since knowledge on ICEC is still in its early stage, we conclude this review with our own views and proposals on the future perspectives for the research in ICEC.
... Furthermore, no diffraction peaks of a separate ZnS phase are observed, indicating that the ZnS shell successfully formed on Ru:InP QDs. 41 XRD and TEM results of Ru-doped InP (G-InP) at higher Ru/In ratios (0.005 and 0.01) are also given in Figures S1 and S2, indicating similar trends for the Ru:InP sample with a Ru/In ratio of 0.003. ...
... First, it has been previously shown that oxides (e.g., ZnO) on InP can increase the PLQY of the core QDs. 41,43 Hence, the measured Ru−O−P oxide phase on the surface of QDs (see Discussion part) may also increase the PLQY of the InP core QDs. In addition, the potential diffusion of the dopant ions from the surface to the inside of QDs can passivate the nonradiative traps. ...
... For that, we integrated the QDs on blue LED chips (with a wavelength of 460 nm) in the liquid state to conserve the PLQY and reduce the host material effect. 41,53 We selected polydimethylsiloxane (PDMS) elastomer to prepare transparent polymeric lenses due to its scalable and low-cost production. 54 Moreover, PDMS can recover its surface after the injection and hold the liquid on top of the blue LED chip without any leakage. ...
... In particular, the energy gap between the conduction and valence bands increases as the size of QDs decreases, providing extended stabilization to the charge-separated state [254]. The highest photoluminescence quantum yields have been reported for cadmium containing nanocrystals, such as CdS, CdSe, and CdTe; thus, research on environmentally friendly and highly efficient QDs is growing [255,256]. Nature developed an astonishing light-harvesting unit, namely, photosystem I (PSI, Figure 6h). It is the light-harvesting machinery found in bacterial reaction centers and works in synergy with photosystem II (PSII) to achieve photosynthesis [201,257]. ...
The extraordinary potential of hydrogen as a clean and sustainable fuel has sparked the interest of the scientific community to find environmentally friendly methods for its production. Biological catalysts are the most attractive solution, as they usually operate under mild conditions and do not produce carbon-containing byproducts. Hydrogenases promote reversible proton reduction to hydrogen in a variety of anoxic bacteria and algae, displaying unparallel catalytic performances. Attempts to use these sophisticated enzymes in scalable hydrogen production have been hampered by limitations associated with their production and stability. Inspired by nature, significant efforts have been made in the development of artificial systems able to promote the hydrogen evolution reaction, via either electrochemical or light-driven catalysis. Starting from small-molecule coordination compounds, peptide- and protein-based architectures have been constructed around the catalytic center with the aim of reproducing hydrogenase function into robust, efficient, and cost-effective catalysts. In this review, we first provide an overview of the structural and functional properties of hydrogenases, along with their integration in devices for hydrogen and energy production. Then, we describe the most recent advances in the development of homogeneous hydrogen evolution catalysts envisioned to mimic hydrogenases.
... [5][6][7] Recent innovations in InP-based QD emitters have incorporated strategies such as surface oxide removal by HF treatment prior to shelling with a wider band gap material 6,8 , elimination of indium defects in the shell through extra purification steps prior to shell growth 7 , and careful engineering of core/shell band alignment through tuning the core size and shell thickness 3,5,9 or the composition of the core, the inner shell, and the outer shell layers. [10][11][12][13] Surface oxide defects must be considered in the design of bright and narrow InP QD emitters. Many studies have reported on both the benefits and challenges associated with oxidic species at the core/shell interface. ...
We demonstrate colloidal, layer-by-layer growth of metal oxide shells on InP quantum dots (QDs) at room temperature. We show with computational modeling that native InP QD surface oxides give rise to nonradiative pathways due to the presence of surface-localized dark states near the band edges. Replacing surface indium with zinc to form a ZnO shell results in reduced nonradiative decay and a density of states at the valence band edge that resembles defect-free, stoichiometric InP. We then developed a synthetic strategy using stoichiometric amounts of common atomic layer deposition precursors in alternating cycles to achieve layer-by-layer growth. Metal oxide-shelled InP QDs show bulk and local structural perturbations as determined by X-ray diffraction and extended X-ray absorption fine structure spectroscopy. Upon growing ZnSe shells of varying thickness on the oxide-shelled QDs, we observe increased photoluminescence quantum yields and narrowing of the emission linewidths that we attribute to decreased ion diffusion to the shell, as supported by P X-ray emission spectroscopy. These results present a versatile strategy to control QD interfaces for novel heterostructure design by leveraging surface oxides. This work also contributes to our understanding of the connections between structural complexity and PL properties in technologically relevant colloidal optoelectronic materials.
... Quantum dots are nano-sized semiconductor crystals capable of emitting a wide range of size-dependent fluorescence [1,2]. Due to their unique composition and stable structure, quantum dots possess a set of desirable characteristics, such as photobleaching resistance and high quantum yield, making them highly appealing for various technologies [3][4][5]. QDs are particularly sought after for their promising biomedical applications, including cell tracking, drug delivery systems, disease detection, tumor detection, and antimicrobial remedies [6][7][8][9][10]. Furthermore, quantum dots are currently present in many high-demand commercialized products, including electronic devices, solar cells, and cosmetics [11][12][13][14]. ...
Quantum dots are nanoparticles (2–10 nm) that emit strong and tunable fluorescence. Quantum dots have been heavily used in high-demand commercialized products, research, and for medical purposes. Emerging concerns have demonstrated the negative impact of quantum dots on living cells; however, the intracellular trafficking of QDs in yeast cells and the effect of this interaction remains unclear. The primary goal of our research is to investigate the trafficking path of red cadmium selenide zinc sulfide quantum dots (CdSe/ZnS QDs) in Saccharomyces cerevisiae and the impact QDs have on yeast cellular dynamics. Using cells with GFP-tagged reference organelle markers and confocal microscopy, we were able to track the internalization of QDs. We found that QDs initially aggregate at the exterior of yeast cells, enter the cell using clathrin-receptor-mediated endocytosis, and distribute at the late Golgi/trans-Golgi network. We also found that the treatment of red CdSe/ZnS QDs resulted in growth rate reduction and loss of polarized growth in yeast cells. Our RNA sequence analysis revealed many altered genes. Particularly, we found an upregulation of DID2, which has previously been associated with cell cycle arrest when overexpressed, and a downregulation of APS2, a gene that codes for a subunit of AP2 protein important for the recruitment of proteins to clathrin-mediated endocytosis vesicle. Furthermore, CdSe/ZnS QDs treatment resulted in a slightly delayed endocytosis and altered the actin dynamics in yeast cells. We found that QDs caused an increased level of F-actin and a significant reduction in profilin protein expression. In addition, there was a significant elevation in the amount of coronin protein expressed, while the level of cofilin was unchanged. Altogether, this suggests that QDs favor the assembly of actin filaments. Overall, this study provides a novel toxicity mechanism of red CdSe/ZnS QDs on yeast actin dynamics and cellular processes, including endocytosis.
... One effective approach comprises synthesizing the core/shell QDs with engineered quasi-type II band alignment such as CdSe/CdS, 16 InP/ZnO core/thick shell, 17 and InP/ZnO/ZnS core/shell/ shell QDs. 18 Another strategy is the reduction of the optical density of the QDs inside the LED architecture to suppress the reabsorption losses and replacing the QD content with phosphors to compensate for the efficiency. 19,20 Moreover, to increase the color conversion efficiency, photonic crystals incorporating green-and red-emitting QDs are utilized, which boosts the QD light extraction and blue-light absorption efficiency. ...
Colloidal nanocrystals have great potential for next-generation solid-state lighting due to their outstanding emission and absorption tunability via size and morphology, narrow emission linewidth, and high photoluminescence quantum yield (PLQY). However, the losses due to self- and interabsorption among multitudes of nanocrystals significantly decrease external quantum yield levels of light-emitting diodes (LEDs). Here, we demonstrate efficient white LEDs via CdSe/CdS dot to “dot-in-rod” transition that enabled a large Stokes shift of 780 meV and significantly reduced absorption losses when used in conjunction with near-unity PLQY ZnCdSe/ZnSe quantum dots (QDs) emitting at the green spectral range. The optimized incorporation of nanocrystals in a liquid state led to the white LEDs with an ultimate external quantum efficiency (EQE) of 42.9%, with a net increase of EQE of 10.3% in comparison with white LEDs using CdSe/CdS dots. Therefore, combinations of nanocrystals with different nanomorphologies hold high promise for efficient white LEDs.
... Yet, there have been reservations regarding in vivo usage due to their high toxicity profile [18,55,56,[82][83][84]. It has been assumed that the toxicity of cadmium quantum dots likely stems from the toxic cadmium ion content [23], and, therefore, research for a cadmium-free alternative has been ongoing in recent years [49,85,86]. ...
Quantum dots are nanocrystals with bright and tunable fluorescence. Due to their unique property, quantum dots are sought after for their potential in several applications in biomedical sciences as well as industrial use. However, concerns regarding QDs' toxicity toward the environment and other biological systems have been rising rapidly in the past decade. In this mini-review, we summarize the most up-to-date details regarding quantum dots' impacts, as well as QDs' interaction with mammalian organisms, fungal organisms, and plants at the cellular, tissue, and organismal level. We also provide details about QDs' cellular uptake and trafficking, and QDs' general interactions with biological structures. In this mini-review, we aim to provide a better understanding of our current standing in the research of quantum dots, point out some knowledge gaps in the field, and provide hints for potential future research.
... [5][6][7] Recent innovations in InP-based quantum dot emitters have incorporated strategies such as surface oxide removal by HF treatment prior to wider band gap shelling 6,8 , elimination of indium defects in the shell through extra purification steps prior to shell growth 7 , and careful engineering of core/shell band alignment through tuning the core size and shell thickness 3,5,9 or the composition of the core, the inner shell, and the outer shell layers. [10][11][12][13] Surface oxide defects must be considered in the design of bright and narrow InP QD emitters. Many studies have reported both detriments and advantages associated with oxidic species at the core/shell interface. ...
We demonstrate colloidal, layer-by-layer growth of metal oxide shells on InP quantum dots (QDs) at room temperature. First, computational modeling demonstrates that native InP surface oxides give rise to increased nonradiative pathways due to the presence of surface-localized dark states near the band edges. Replacing surface indium with zinc to form a ZnO shell results in reduced nonradiative decay and a density of states at the valence band maximum that resembles defect-free, stoichiometric InP. Motivated by these findings, we developed a synthetic strategy using stoichiometric amounts of common ALD precursors in alternating cycles. Metal oxide-shelled InP QDs show bulk and local structural perturbations as determined by X-ray diffraction extended X-ray absorption fine structure spectroscopy. Upon growing ZnSe shells of varying thickness on the oxide-shelled QDs, we observe increased photoluminescence quantum yields and narrowing of the emission linewidths, which we hypothesize to be attributable to decreased ion diffusion to the shell, as supported by P X-ray emission spectroscopy. These results present a generalizable and versatile strategy to control QD interfaces for novel heterostructure design by leveraging surface oxides. This work also contributes to our understanding of how to use structural complexity for improved PL properties of technologically relevant colloidal optoelectronic materials.
