InP QDs Research Articles

Giant Pyramidal Near‐Infrared InP/ZnS Quantum Dots with Size Over 15 nm for Cell Imaging

AbstractIn recent years, near‐infrared quantum dots (NIR QDs) have emerged as a promising candidate for biological imaging owing to their strong fluorescence penetrating into biological tissues and high imaging signal‐to‐noise ratio. Among various materials, InP QDs are environmentally friendly and have a relatively narrow bandgap of 1.35 eV, which provides a possibility for their emission wavelength to extend to the near‐infrared region. However, the strong reactivity of the precursor of phosphorus makes it challenging to synthesize NIR InP QDs, as it leads to rapid nucleation of the InP core. Herein, a method of epitaxial growth is reported to synthesize NIR InP QDs. Through high‐temperature nucleation and low‐temperature epitaxial growth, NIR InP QDs larger than 15 nm in size and with an emission wavelength of 807 nm are successfully synthesized. Furthermore, by removing InPOx defects on the surface of the core through HF etching, the quantum yield (QY) is increased from 6% to 12%. Ligand exchange successfully converted oil‐soluble ligands into water‐soluble ones, leading to excellent performance in cell imaging. The study provides a promising approach to the synthesis of desirable NIR InP QDs for use in biomedical imaging applications.

Empirical band-gap correction for LDA-derived atomic effective pseudopotentials

Atomic effective pseudopotentials enable atomistic calculations at the level of accuracy of density functional theory for semiconductor nanostructures with up to fifty thousand atoms. Since they are directly derived from ab-initio calculations performed in the local density approximation (LDA), they inherit the typical underestimated band gaps and effective masses. We propose an empirical correction based on the modification of the non-local part of the pseudopotential and demonstrate good performance for bulk binary materials (InP, ZnS, HgTe, GaAs) and quantum dots (InP, CdSe, GaAs) with diameters ranging from 1.0 nm to 4.45 nm. Additionally, we provide a simple analytic expression to obtain accurate quasiparticle and optical band gaps for InP, CdSe, and GaAs QDs, from standard LDA calculations.

Metal-Solvent Complex Formation at the Surface of InP Colloidal Quantum Dots.

The surface chemistry of colloidal semiconductor nanocrystals (QDs) profoundly influences their physical and chemical attributes. The insulating organic shell ensuring colloidal stability impedes charge transfer, thus limiting optoelectronic applications. Exchanging these ligands with shorter inorganic ones enhances charge mobility and stability, which is pivotal for using these materials as active layers for LEDs, photodetectors, and transistors. Among those, InP QDs also serve as a model for surface chemistry investigations. This study focuses on group III metal salts as inorganic ligands for InP QDs. We explored the ligand exchange mechanism when metal halide, nitrate, and perchlorate salts of group III (Al, In Ga), common Lewis acids, are used as ligands for the conductive inks. Moreover, we compared the exchange mechanism for two starting model systems: InP QDs capped with myristate and oleylamine as X- and L-type native organic ligands, respectively. We found that all metal halide, nitrate, and perchlorate salts dissolved in polar solvents (such as n-methylformamide, dimethylformamide, dimethyl sulfoxide, H2O) with various polarity formed metal-solvent complex cations [M(Solvent)6]3+ (e.g., [Al(MFA)6]3+, [Ga(MFA)6]3+, [In(MFA)6]3+), which passivated the surface of InP QDs after the removal of the initial organic ligand. All metal halide capped InP/[M(Solvent)6]3+ QDs show excellent colloidal stability in polar solvents with high dielectric constant even after 6 months in concentrations up to 74 mg/mL. Our findings demonstrate the dominance of dissociation-complexation mechanisms in polar solvents, ensuring colloidal stability. This comprehensive understanding of InP QD surface chemistry paves the way for exploring more complex QD systems such as InAs and InSb QDs.

Magnesium ions enhanced core-shell lattice matching for Narrow-Band green emission indium phosphide QDs

Indium phosphide QDs have emerged as a promising candidate for the next generation optoelectronic applications. However, the optical performance of InP QDs still lags behind that of CdSe-based QDs, partly due to surface traps induced by the lattice mismatch between InP and ZnSe. Herein, based on (DMA)3P, we designed an alloyed inner-shell structure of InP/Zn(Mg)Se/ZnS QDs. The dual-function mechanism of the Zn(Mg)Se was revealed, which effectively mitigates the lattice mismatch between the core and shell toreduce the emission of surface defect states, resulting in narrowed emission peaks (FWHM ∼ 36 nm). While the increased band gap of Zn(Mg)Se confines the exciton delocalization from core to shell, thereby reducing the non-radiative relaxation of carriers at the defect states in the shell. This discovery provides a strategy to improve the color purity and luminescence efficiency of InP QDs. By combining blue LED chips with InP/Zn(Mg)Se/ZnS, a white light-emitting diode (QLED) with a high luminous efficiency of 63 lm/W was obtained. Furthermore, the realization of QDs arrays with 10 μm pixel dots by inkjet printing technology and the fabrication of white-light emitting Micro-LEDs by combining QDs films with Micro-LED chip arrays demonstrate the potential application of InP QDs in high-efficiency optoelectronic devices (LEDs/micro-LEDs).

Efficient and environmentally friendly white light-emitting diodes with InP-based quantum dots embedded in mesoporous silica

As one of the promising next-generation light conversion materials, indium phosphide quantum dots (InP QDs) deserve much attention due to their great optical performances and environmentally friendly properties in particular. Herein, InP-based QDs are embedded into mesoporous SBA-15 and solid QDs/SBA-15 composites are prepared, which exhibit 1.5 times higher photoluminescence quantum yield (PLQY) and narrower full width of half maximum (FWHM) than traditional QDs powder thanks to the reduction of light reabsorption and the optical waveguide effect of mesoporous structure. These advantages contribute to the performance enhancement of light-emitting diodes (LEDs). The luminous efficacy of the LED with green QDs/SBA-15 is 99.49 lm/W, which is higher than that of QDs powder (66.14 lm/W). In addition, the white LED fabricated with green and red InP-based QDs/SBA-15 shows luminous efficacy of 61.38 lm/W. More importantly, the luminous efficacy of the white LED is improved to 129.62 lm/W when using the K2SiF6:Mn4+ instead of red InP-based QDs/SBA-15, because the K2SiF6:Mn4+ does not absorb the emission from green InP-based QDs/SBA-15. This value is higher than those white LEDs with InP-based QDs reported previously. It is believed that this study demonstrates the promising potential of InP-based QDs for optoelectronic applications.

Eu3+-based InP/ZnS quantum dot fluorescence platform for multi-color and sensitive visualization of tetracycline

A turn-on type ratiometric fluorescence sensing system of blue quantum dot Eu-MPA-InP/ZnS was established for multi-color visualization determination of tetracycline (TC). Mercaptopropionic acid (MPA)-capped InP/ZnS quantum dots (MPA-InP/ZnS QDs) both modify the hydrophilicity of InP/ZnS QDs and serve as a scaffold for coordinating of Eu3+ ions. The blue fluorescence of Eu-MPA-InP/ZnS at 478 nm is reduced by the TC through the inner filter effect (IFE) under a single excitation wavelength of 365 nm. Rich colour gradients and a highly discriminative colour change were features of this multicolour response to TC, which allowed visual quantification of TC in a dose-dependent manner. Furthermore, by cross-linking Eu-MPA-InP/ZnS with agarose (Aga.), a mouldable Eu-MPA-InP/ZnS@Aga 96-well gel sensing device was designed to serve as a handheld sensor for on-site detection of TC. This probe expands the use of InP QDs in analytical sensing and has been effectively applied to the visual detection of tetracycline in milk and the environment.

Optical gain and entanglement through dielectric confinement and electric field in InP quantum dots.

Quantum dots are widely recognized for their advantageous light-emitting properties. Their excitonic fine structure along with the high quantum yields offers a wide range of possibilities for technological applications. However, especially for the case of colloidal QDs, there are still characteristics and properties which are not adequately controlled and downgrade their performance for applications which go far beyond the simple light emission. Such a challenging task is the ability to manipulate the energetic ordering of exciton and biexciton emission and subsequently control phenomena such as Auger recombination, optical gain and photon entanglement. In the present work we attempt to engineer this ordering for the case of InP QDs embedded in polymer matrix, by means of their size, the dielectric confinement and external electric fields. We employ well tested, state of the art theoretical methods, in order to explore the conditions under which the exciton-biexciton configuration creates the desired conditions either for optical gain or photon entanglement. Indeed, this appears to be feasible for QDs with small diameters (1 nm, 1.5 nm) embedded in a host material with high dielectric constant and additional external electric fields. These findings offer a new design principle which might be complementary to the well-established type II core-shell QDs approach for achieving electron-hole separation.

Surface Chemistry Dictates the Enhancement of Luminescence and Stability of InP QDs upon c-ALD ZnO Hybrid Shell Growth.

Indium phosphide quantum dots (InP QDs) are a promising example of Restriction of Hazardous Substances directive (RoHS)-compliant light-emitting materials. However, they suffer from low quantum yield and instability upon processing under ambient conditions. Colloidal atomic layer deposition (c-ALD) has been recently proposed as a methodology to grow hybrid materials including QDs and organic/inorganic oxide shells, which possess new functions compared to those of the as-synthesized QDs. Here, we demonstrate that ZnO shells can be grown on InP QDs obtained via two synthetic routes, which are the classical sylilphosphine-based route and the more recently developed aminophosphine-based one. We find that the ZnO shell increases the photoluminescence emission only in the case of aminophosphine-based InP QDs. We rationalize this result with the different chemistry involved in the nucleation step of the shell and the resulting surface defect passivation. Furthermore, we demonstrate that the ZnO shell prevents degradation of the InP QD suspension under ambient conditions by avoiding moisture-induced displacement of the ligands from their surface. Overall, this study proposes c-ALD as a methodology for the synthesis of alternative InP-based core@shell QDs and provides insight into the surface chemistry that results in both enhanced photoluminescence and stability required for application in optoelectronic devices and bioimaging.

Population balance modeling of InP quantum dots: Experimentally enabled global optimization to identify unknown material parameters

Despite great progress in the synthetic chemistry of InP QDs, a predictive model to describe their temporal formation is still missing. In this work, we introduce a population balance model incorporating liquid phase reactions, homogeneous nucleation and reaction-limited growth of InP supported with the highly reproducible and reliable experimental data acquired from an automated robotic synthesis platform. A comparison between experimental kinetic data (different initial concentrations and temperatures) and simulations was made. The proposed model describes the temporal evolution of solid concentration, particle diameter and particle size distribution very well. The quantitative agreement between experiments and simulations was only achieved by global optimization to identify unknown and hardly measurable material parameters and kinetic constants such as surface energy, growth rate constants or activation energies. We see this model rendering the first step towards the development of more refined models that enable rigorous optimization and control of the production process for III-V semiconductors.

Aminophosphine-based continuous liquid-phase synthesis of InP and InP/ZnS quantum dots in a customized tubular flow reactor

Continuous flow synthesis of InP QDs and InP/ZnS core/shell QDs using a premixed precursor solution and a customized tubular flow reactor setup.

Advances, Challenges, and Perspectives for Heavy‐Metal‐Free Blue‐Emitting Indium Phosphide Quantum Dot Light‐Emitting Diodes

AbstractQuantum dot light‐emitting diodes (QLEDs), regarded as promising candidates in the next‐generation display, have attracted much attention recently. In spite of the outstanding performance of cadmium‐based (Cd‐based) QLEDs, the toxicity of Cd hinders their wide application. Indium phosphide quantum dots (InP QDs) with heavy‐metal‐free feature and competitive performance are considered to be able to replace Cd‐based QDs as emitting layer in the QLEDs. Much progress is obtained in the red‐emitting and green‐emitting InP‐based QLEDs. However, the blue‐emitting ones are faced with great challenges and are demanded on full‐color display urgently, which is limited by the inferior performance of blue‐emitting InP QDs and lack of investigations about their QLED devices. In this review, the encountered challenges for high‐quality blue‐emitting InP QDs are presented. Common strategies for blue‐emitting InP QDs, including size engineering, composition engineering, and surface engineering are presented and analyzed. The progress of blue‐emitting InP‐based QLEDs, which strongly relies on the advances of materials, is also summarized. Finally, some perspectives from device physics are provided and discussed to inspire more efficient strategies toward blue‐emitting InP‐based QLEDs.

A Water-Free In Situ HF Treatment for Ultrabright InP Quantum Dots.

Indium phosphide quantum dots are the main alternative for toxic and restricted Cd-based quantum dots for lighting and display applications, but in the absence of protecting ZnSe and/or ZnS shells, InP quantum dots suffer from low photoluminescence quantum yields. Traditionally, HF treatments have been used to improve the quantum yield of InP to ∼50%, but these treatments are dangerous and not well understood. Here, we develop a postsynthetic treatment that forms HF in situ from benzoyl fluoride, which can be used to strongly increase the quantum yield of InP core-only quantum dots. This treatment is water-free and can be performed safely. Simultaneous addition of the z-type ligand ZnCl2 increases the photoluminescence quantum yield up to 85%. Structural analysis via XPS as well as solid state and solution NMR measurements shows that the in situ generated HF leads to a surface passivation by indium fluoride z-type ligands and removes polyphosphates, but not PO3 and PO4 species from the InP surface. With DFT calculations it is shown that InP QDs can be trap-free even when PO3 and PO4 species are present on the surface. These results show that both polyphosphate removal and z-type passivation are necessary to obtain high quantum yields in InP core-only quantum dots. They further show that core-only InP QDs can achieve photoluminescence quantum yields rivalling those of InP/ZnSe/ZnS core/shell/shell QDs and the best core-only II-VI QDs.

Inkjet-printed blue InP/ZnS/ZnS quantum dot light-emitting diodes

Inkjet-printed quantum dot light-emitting diodes (QLEDs) are considered to be ideal candidates for use in full-color displays. However, preparation of eco-friendly blue InP QLEDs using inkjet printing techniques remains rather challenging due to the inferior optical properties of QDs. Here, we present the first efficient method for generating inkjet-printed QLEDs with high color purity using blue InP/ZnS/ZnS QDs as the emitting layer. A two-step heat-up and thick shell strategy was employed for the preparation of blue InP/ZnS/ZnS QDs with a photoluminescence (PL) peak at 465 nm, full width at half-maximum of 38 nm, and PL quantum yield (QY) of ∼ 96 %, which are the records for blue InP QDs. We found that the use of a zinc iodide precursor and anhydrous oxygen reaction environment is critical to determining InP core size, and the size distribution of InP cores can be improved by separating formation of InP magic size clusters and cores via a heat-up step at low temperature. We used two kind of zinc precursors to facilitate shell growth, and the engineered shell thickness suppresses energy transfer, enabling InP/ZnS/ZnS QDs film with high PLQYs and contributing to efficient inkjet printing of QLEDs. These results can facilitate the development of blue InP QLEDs for large-area electroluminescent full-color displays.

Engineering Core Size of InP Quantum Dot with Incipient ZnS for Blue Emission

AbstractBlue indium phosphide quantum dot (InP QD) is an emerging colloidal semiconductor nanocrystal, considered as a promising next‐generation photoactive material for light‐emitting purposes. Despite the tremendous progress in blue InP QDs, the synthetic method for tailoring InP core size to realize the blue‐emissive QDs still lags behind. This work suggests a synthetic method for blue‐emitting InP QDs by engineering the core size with an incipient ZnS (i‐ZnS) shell. The formation of i‐ZnS complexes, before the tris(trimethylsilyl)phosphine injection (e.g., before core growth process), restrains the overgrowth of InP nuclei by rapidly forming a ZnS shell on its surface, thereby resulting in further dwarfed InP cores. With additional ZnS shell coating, the blue QDs exhibit a photoluminescence quantum yield of ≈52% at 483 nm. The origin of bandgap diminution with the increase of shell thickness, or with the utilization of ZnSe shell is unraveled via the first‐principles density functional theory simulations. Simulational evidence on InP‐core densification with the shell coating, along with accompanying changes in chemical and structural properties, is presented. The blue‐emitting InP QD device shows a maximum luminance of 1162 cd m−2 and external quantum efficiency of 1.4%.

Narrowing of the Particle Size Distribution of InP Quantum Dots for Green Light Emission by Synthesis in Micro‐Flow Reactor

AbstractQuantum dots (QDs), with their superior efficiency, color purity, and color controllability, are expected to be applied in next generation displays and other devices. The development of methods to synthesize QDs still provide equivalent or better performance without restricted substances such as cadmium (Cd) and lead (Pb) is a meaningful challenge. In this study, InP QDs were synthesized using the micro‐flow reactor (MFR) with an extremely high rate of temperature change to shorten the nucleation time and avoid Ostwald ripening during QD synthesis. As a result, the particle size distribution was narrowed and the emission full‐width at half maximum (FWHM) was reduced to less than 40 nm. While other related studies have tried complex methods, in our efforts, it was achieved by using the simple MFR. These results can accelerate the application of InP QDs as a promising option for commercially viable QDs.

Photoactivated Indium Phosphide Quantum Dots Treat Multidrug-Resistant Bacterial Abscesses In Vivo.

The increasing prevalence of drug-resistant bacterial strains is causing illness and death in an unprecedented number of people around the globe. Currently implemented small-molecule antibiotics are both increasingly less efficacious and perpetuating the evolution of resistance. Here, we propose a new treatment for drug-resistant bacterial infection in the form of indium phosphide quantum dots (InP QDs), semiconductor nanoparticles that are activated by light to produce superoxide. We show that the superoxide generated by InP QDs is able to effectively kill drug-resistant bacteria in vivo to reduce subcutaneous abscess infection in mice without being toxic to the animal. Our InP QDs are activated by near-infrared wavelengths with high transmission through skin and tissues and are composed of biocompatible materials. Body weight and organ tissue histology show that the QDs are nontoxic at a macroscale. Inflammation and oxidative stress markers in serum demonstrate that the InP QD treatment did not result in measurable effects on mouse health at concentrations that reduce drug-resistant bacterial viability in subcutaneous abscesses. The InP QD treatment decreased bacterial viability by over 3 orders of magnitude in subcutaneous abscesses formed in mice. These InP QDs thus provide a promising alternative to traditional small-molecule antibiotics, with the potential to be applied to a wide variety of infection types, including wound, respiratory, and urinary tract infections.

65‐2: Red Electroluminescence Quantum Dot Devices (EL‐QD) with Improved Efficiency and Lifetime

By optimizing the interface between charge transport layer and quantum dots in EL‐QD devices based on InP QDs, 1.4‐fold improvement in the efficiency and 3‐fold increasing lifetime are obtained.

P‐59: The Linewidth Gaps for Quantum Dots and Micro LEDs

The emission linewidth of light emitters such as quantum dots and µLEDs significantly affect their performance in displays, but the gaps between experimental data and the fundamental limits have not been clearly quantified. Here, a survey of experimental data and simple theoretical models are used to delineate large linewidth gaps for both QDs and µLEDs for visible wavelengths. For CdSe QDs the linewidth gap is ~1.5‐3 times the fundamental limit. For InP QDs the linewidth gap is ~2‐4 times the fundamental limit. For GaN‐based µLEDs the gap is ~1.5‐3 times the fundamental linewidth limit. It is also shown that both state‐of‐the‐art OLEDs and GaN LEDs have similar linewidths over the visible wavelength range. Moreover, it is found that one of the value propositions of using inorganic GaN µLEDs (better color gamut) is yet to be demonstrated, and QDs as color conversion for red and green will likely prove beneficial until the “ideal state” of GaN based µLEDs can be proven/solved.

Extending the Near-Infrared Emission Range of Indium Phosphide Quantum Dots for Multiplexed In Vivo Imaging.

This report of the reddest emitting indium phosphide quantum dots (InP QDs) to date demonstrates tunable, near-infrared (NIR) photoluminescence (PL) as well as PL multiplexing in the first optical tissue window while avoiding toxic constituents. This synthesis overcomes the InP "growth bottleneck" and extends the emission peak of InP QDs deeper into the first optical tissue window using an inverted QD heterostructure, specifically ZnSe/InP/ZnS core/shell/shell nanoparticles. The QDs exhibit InP shell thickness-dependent tunable emission with peaks ranging from 515-845 nm. The high absorptivity of InP yields effective photoexcitation of the QDs with UV, visible, and NIR wavelengths. These nanoparticles extend the range of tunable direct-bandgap emission from InP-based nanostructures, effectively overcoming a synthetic barrier that has prevented InP-based QDs from reaching their full potential as NIR imaging agents. Multiplexed lymph node imaging in a mouse model demonstrates the potential of the NIR-emitting InP particles for in vivo imaging.

Stability enhancement of InP quantum dot/poly(methyl methacrylate) nanocomposites for light-emitting diode applications by grafting thermoresponsive poly(N-isopropylacrylamide)

Nanocomposites containing thermoresponsive poly(N-isopropylacrylamide)-grafted InP QDs exhibit enhanced stability against high temperature and humidity and luminescence properties.