Indium Phosphide Quantum Dots Research Articles

Siloxane-based oligomer ligands of indium phosphide quantum dots for improving dispersion in a siloxane matrix

The ligands of indium phosphide (InP) quantum dots (QDs) were modified with siloxane-based oligomers in a two-step process to improve the dispersion of InP QDs in a siloxane-based matrix. Oleic acid ligands on InP QDs (InP-OA) were exchanged with 6-mercapto-1-hexanol. Then, the hydroxyl functional groups (–OH) of the ligands were induced to react with poly(dimethylsiloxane), diglycidyl ether terminated (PDMS-DGE) by a ring-opening reaction of epoxide. The chemical bonding between the hydroxyl groups and PDMS-DGE was confirmed by Fourier-transform infrared (FT-IR) spectroscopy. The synthesized InP QDs with PDMS-DGE ligands (InP-PDMS-DGE) were blended with acrylate-siloxane polymers to produce color conversion QD films. The photoluminescence (PL) intensity of the QD films with the InP-PDMS-DGE QDs was improved by 2.3 times compared with that of InP-OA QDs. The color conversion efficiency of the QD films was determined using a blue light-emitting diode (LED), and the QD film containing InP-PDMS-DGE QDs demonstrated a conversion efficiency of 21%, compared to a lower efficiency of 17% for a film containing InP-OA QDs. The stability of the InP-PDMS-DGE film was tested at 85°C with a relative humidity (RH) of 85%, demonstrating an improvement of 28% compared to that with an InP-OA film.

Evidence and Structural Insights into a Ligand-Mediated Phase Transition in the Solvated Ligand Shell of Quantum Dots.

As synthesized, nanocrystal surfaces are typically covered in coordinating organic ligands, and the degree of packing and order of these ligands are ongoing questions in the field of colloidal nanocrystals, particularly in the solution state. Recently, isothermal titration calorimetry coupled with 1H NMR has been used to probe ligand exchanges on colloidal quantum dots, revealing the importance of the composition of the ligand shell on exchange thermodynamics. Previous work has shown that the geometry and length of a ligand's aliphatic chain can influence the thermodynamics of exchange. This has been attributed to interligand interactions, and the use of a modified Ising model simulation to account for these collective effects has been critical in describing these reactions. In this report, we explore the reaction between indium phosphide quantum dots and zinc chloride on a size series of nanocrystals capped with two different lengths of aliphatic, straight-chain carboxylate ligands to investigate the effect that nanocrystal size has on these interligand interactions. We demonstrate that interligand interactions increase as the nanocrystal size increases, changing the thermodynamics of the ligand exchange reaction. Critically, we show that a self-consistent model of these ligand exchanges does not fit the data without the use of a phase transition term in the model and that the strength of this phase transition depends on the nanocrystal size. Combined with solution state X-ray diffraction, these results provide indirect evidence that ligands are ordered on nanocrystals in the solution state.

On the Electroluminescence of InP Quantum Dots with Varied ZnSe/ZnS Shell Thickness

Quantum dots (QDs) have emerged as a highly promising material for future display applications, offering advantages such as tunable emission wavelengths, narrow linewidths, and the ability to cover a broad color gamut. Traditionally, cadmium selenide (CdSe) QDs have dominated the electroluminescence (EL) QD light-emitting Diode (QLED) landscape. However, the presence of toxic metal cadmium in CdSe QDs has raised environmental and safety concerns. In recent years, indium phosphide (InP) materials, free from heavy metals, have become a focal point in EL QLED research. For InP EL QLED, the shell structure of InP/ZnSe/ZnS core/shell/shell QDs plays a crucial role in influencing carrier behavior and device performance. In this study, we prepare InP QDs with three different shell thickness, including ZnSeS shell with thickness of more than 6 nm (InP/ZnSe/ZnS QD size > 15 nm), and explore their EL properties. The research aims to investigate the potential mechanisms governing the interplay between shell thickness and carrier recombination, contributing to the optimization of InP QLEDs. Figure 1

Unity quantum yield of InP/ZnSe/ZnS quantum dots enabled by Zn halide-derived hybrid shelling approach

Environment-benign indium phosphide (InP) quantum dots (QDs) show great promise as visible emitters for next-generation display applications, where bright and narrow emissivity of QDs should be required toward high-efficiency, high-color reproducibility. The photoluminescence (PL) performance of InP QDs has been consistently, markedly improved, particularly owing to the exquisite synthetic control over core size homogeneity and core/shell heterostructural variation. To date, synthesis of most high-quality InP QDs has been implemented by using zinc (Zn) carboxylate as a shell precursor that unavoidably entails the formation of surface oxide on InP core. Herein, we demonstrate synthesis of superbly bright, color-pure green InP/ZnSe/ZnS QDs by exploring an innovative hybrid Zn shelling approach, where Zn halide (ZnX2, X = Cl, Br, I) and Zn oleate are co-used as shell precursors. In the hybrid Zn shelling process, the type of ZnX2 is found to affect the growth outcomes of ZnSe inner shell and consequent optical properties of the resulting heterostructured InP QDs. Enabled by not only the near-complete removal of the oxide layer on InP core surface through the hybrid Zn shelling process but the controlled growth rate of ZnSe inner shell, green InP/ZnSe/ZnS QDs achieve a record quantum yield (QY) up to unity along with a highly sharp linewidth of 32 nm upon growth of an optimal ZnSe shell thickness. This work affords an effective means to synthesize high-quality heterostructured InP QDs with superb emissive properties.

Highly Luminescent Shell-Less Indium Phosphide Quantum Dots Enabled by Atomistically Tailored Surface States.

Contrary to the prevailing notion that shell structures arise from the intricate chemistry and surface defects of InP quantum dots (QDs), an innovative strategy that remarkably enhances the luminescence efficiency of core-only InP QDs to over 90% is introduced. This paradigm shift is achieved through the concurrent utilization of group 2 and 3 metal-derived ligands, providing an effective remedy for surface defects and facilitating charge recombination. Specifically, a combination of Zn carboxylate and Ga chloride is employed to address the undercoordination issues associated with In and P atoms, leading to the alleviation of in-gap trap states. The intricate interplay and proportional ratio between Ga- and Zn-containing ligands play pivotal roles in attaining record-high luminescence efficiency in core-only InP QDs, as successfully demonstrated across various sizes and color emissions. Moreover, the fabrication of electroluminescent devices relying solely on InP core emission opens a new direction in optoelectronics, demonstrating the potential of the approach not only in optoelectronic applications but also in catalysis or energy conversion by charge transfer.

Asymmetric Metal-Carboxylate Complexes for Synthesis of InGaP Alloyed Quantum Dots with Blue Emission.

Indium phosphide (InP) quantum dots (QDs) have attracted significant interest as next-generation light-emitting materials. However, the synthesis of blue-emitting InP-based QDs has lagged behind that of established green- and red-emitting InP QDs. Herein, we present a strategy to synthesize blue-emitting QDs by forming an InGaP alloy composition. The introduction of asymmetric In-carboxylate and Ga-carboxylate complexes resulted in a balanced synthetic reactivity between In-P and Ga-P, leading to the formation of InGaP alloyed QDs. The resultant In1-xGaxP alloyed QDs exhibited a broad range of photoluminescence (PL) tunability, spanning from 535 nm (InP) to 465 nm (In0.62Ga0.38P), depending on the In/Ga ratio used in the synthesis. In contrast, synthesis with symmetric In-carboxylate and Ga-carboxylate complexes produced a core/shell structure of InP/GaP QDs, which did not exhibit a blue shift of the PL peak with Ga addition. By employing a core/shell structure of In0.62Ga0.38P/ZnS QDs, we achieved a PL quantum yield of 42% at 475 nm. This work highlights the material-processing strategy essential for forming alloyed structures in III-V ternary systems.

Development of an aptasensor to target metallo-β-lactamase through Förster resonance energy transfer

The escalating issue of antibiotic resistance in bacteria necessitates innovative detection methods to identify resistance mechanisms promptly. In this study, we present a novel approach for detecting resistance in Pseudomonas aeruginosa, a bacterium known for its metallo-β-lactamase production during the development of antibiotic resistance. We have designed an aptasensor employing Förster resonance energy transfer utilising two distinct methodologies. Initially, indium phosphide quantum dots with a zinc sulphide shell, and gold nanoparticles were utilised as the Förster resonance energy transfer donor-acceptor pair. Although this system demonstrated a response, the efficiency was low. Subsequently, optimisation involved relocating the donor and acceptor in close proximity and incorporating two quantum dots with varying emission wavelengths as the acceptor and donor. This optimisation significantly enhanced the Förster resonance efficiency, resulting in a novel method for detecting metallo-β-lactamase. Förster resonance energy transfer efficiency was increased from 31% to 63% by optimising the distance and donor using a quantum dot-quantum dot pair. Our findings showcase a cheap, rapid and versatile aptasensor with potential applications beyond antibiotic resistance, highlighting its adaptability for diverse scenarios.

Near-Unity Photoluminescence Quantum Yield of Core-Only InP Quantum Dots via a Simple Postsynthetic InF3 Treatment.

Indium phosphide (InP) quantum dots (QDs) are considered the most promising alternative for Cd and Pb-based QDs for lighting and display applications. However, while core-only QDs of CdSe and CdTe have been prepared with near-unity photoluminescence quantum yield (PLQY), this is not yet achieved for InP QDs. Treatments with HF have been used to boost the PLQY of InP core-only QDs up to 85%. However, HF etches the QDs, causing loss of material and broadening of the optical features. Here, we present a simple postsynthesis HF-free treatment that is based on passivating the surface of the InP QDs with InF3. For optimized conditions, this results in a PLQY as high as 93% and nearly monoexponential photoluminescence decay. Etching of the particle surface is entirely avoided if the treatment is performed under stringent acid-free conditions. We show that this treatment is applicable to InP QDs with various sizes and InP QDs obtained via different synthesis routes. The optical properties of the resulting core-only InP QDs are on par with InP/ZnSe/ZnS core-shell QDs, with significantly higher absorption coefficients in the blue, and with potential for faster charge transport. These are important advantages when considering InP QDs for use in micro-LEDs or photodetectors.

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.

Surface Passivation toward Multiple Inherent Dangling Bonds in Indium Phosphide Quantum Dots.

Indium phosphide (InP) quantum dots (QDs) have become the most recognized prospect to be less-toxic surrogates for Cd-based optoelectronic systems. Due to the particularly dangling bonds (DBs) and the undesirable oxides, the photoluminescence performance and stability of InP QDs remain to be improved. Previous investigations largely focus on eliminating P-DBs and resultant surface oxidation states; however, little attention has been paid to the adverse effects of the surface In-DBs on InP QDs. This work demonstrates a facile one-step surface peeling and passivation treatment method for both In- and P-DBs for InP QDs. Meanwhile, the surface treatment may also effectively support the encapsulation of the ZnSe shell. Finally, the generated InP/ZnSe QDs display a narrower full width at half-maximum (fwhm) of ∼48 nm, higher photoluminescence quantum yields (PLQYs) of ∼70%, and superior stability. This work enlarges the surface chemistry engineering consideration of InP QDs and considerably promotes the development of efficient and stable optoelectronic devices.

Pseudohalogen Ammonium Salt-Assisted Syntheses of Large-Sized Indium Phosphide Quantum Dots with Near-Infrared Photoluminescence.

The development of indium phosphide (InP)-based quantum dots (QDs) with a near-infrared (NIR) emission area still lags behind the visible wavelength region and remains problematic. This study describes a one-step in situ pseudohalogen ammonium salt-assisted approach to generate NIR-emitted InP-based QDs with high photoluminescence quantum yields (PLQYs). The coexistence of NH4+ and PF6- ions from NH4PF6 may in situ synchronously etch and passivate the surface oxides and impede the creation of traps under the whole growth process of InP QDs. Experimental findings demonstrated that the in situ pseudohalogen ammonium salt-assisted syntheses technique may feature emission at a full width at half-maximum (fwhm) peak as fine as ∼45 nm and broaden the emission range to around ∼780 nm. A two-step approach for ZnS shells was developed to further improve the PLQY of NIR-emitted InP QDs. Furthermore, the constructed high-power intrinsically stretchable NIR color-conversion film employing the InP-based QDs/polymer composites presented excellent luminescence conversion ability and stretchability.

Quantum Dot Imaging Agents: Haematopoietic Cell Interactions and Biocompatibility.

Quantum dots (QDs) are semi-conducting nanoparticles that have been developed for a range of biological and non-biological functions. They can be tuned to multiple different emission wavelengths and can have significant benefits over other fluorescent systems. Many studies have utilised QDs with a cadmium-based core; however, these QDs have since been shown to have poor biological compatibility. Therefore, other QDs, such as indium phosphide QDs, have been developed. These QDs retain excellent fluorescent intensity and tunability but are thought to have elevated biological compatibility. Herein we discuss the applicability of a range of QDs to the cardiovascular system. Key disease states such as myocardial infarction and stroke are associated with cardiovascular disease (CVD), and there is an opportunity to improve clinical imaging to aide clinical outcomes for these disease states. QDs offer potential clinical benefits given their ability to perform multiple functions, such as carry an imaging agent, a therapy, and a targeting motif. Two key cell types associated with CVD are platelets and immune cells. Both cell types play key roles in establishing an inflammatory environment within CVD, and as such aid the formation of pathological thrombi. However, it is unclear at present how and with which cell types QDs interact, and if they potentially drive unwanted changes or activation of these cell types. Therefore, although QDs show great promise for boosting imaging capability, further work needs to be completed to fully understand their biological compatibility.

Green synthesis of high-quality indium phosphide quantum dots using tripyrrolidine phosphine as a promising phosphorus source for white LED

Indium phosphide quantum dots (InP QDs) have emerged as highly promising contenders for cadmium-based quantum dots, primarily due to their environmentally sustainable attributes. Early methods for synthesizing InP QDs employed tris(trimethylsilyl)phosphine and tris(dimethylamino)phosphine as phosphorus sources. However, the associated toxicity and hazards of these sources have hindered further progress. In this study, we introduce tripyrrolidine phosphine as a safe alternative phosphorus source. This source not only guarantees affordability, but also simplifies recycling and hazardous waste treatment processes. Simultaneously, precise regulation of the Zn precursor during the growth of the ZnS shell has enabled the synthesis of InP QDs of exceptional quality with a prominent emission peak at 525 nm, an impressive photoluminescence quantum yield of 76.11 %, and a narrow half-peak width of 37 nm. This achievement sets a significant precedent for the development of an environmentally friendly InP QD synthesis methodology. Furthermore, the incorporation of the QDs into white LEDs yields compelling outcomes, including color coordinates of (0.33, 0.30) and a measured correlated color temperature of 5637 K. Therefore, this study not only establishes an innovative path for InP QD production, but also drives their broader integration into the realm of white LED applications.

Single- and two-photon-induced Förster resonance energy transfer in InP-mCherry bioconjugates.

Indium phosphide (InP) quantum dots (QDs) have recently garnered considerable interest in the design of bioprobes due to their non-toxic nature and excellent optical properties. Several attempts for the conjunction of InP QDs with various entities such as organic dyes and dye-labeled proteins have been reported, while that with fluorescent proteins remains largely uncharted. This study reports the development of a Förster resonance energy transfer pair comprising glutathione-capped InP/GaP/ZnS QDs [InP(G)] and the fluorescent protein mCherry. Glutathione on InP(G) undergoes effective bioconjugation with mCherry consisting of a hexahistidine tag, and the nonradiative energy transfer is investigated using steady-state and time-resolved measurements. Selective one-photon excitation of InP(G) in the presence of mCherry shows a decay of the emission of the QDs and a concomitant growth of acceptor emission. Time-resolved investigations prove the nonradiative transfer of energy between InP(G) and mCherry. Furthermore, the scope of two-photon-induced energy transfer between InP(G) and mCherry is investigated by exciting the donor in the optical transparency range. The two-photon absorption is confirmed by the quadratic relationship between the emission intensity and the excitation power. In general, near-infrared excitation provides a path for effective light penetration into the tissues and reduces the photodamage of the sample. The two-photon-induced energy transfer in such assemblies could set the stage for a wide range of biological and optoelectronic applications in the foreseeable future.

Ligand Steric Profile Tunes the Reactivity of Indium Phosphide Clusters.

Indium phosphide quantum dots have become an industrially relevant material for solid-state lighting and wide color gamut displays. The synthesis of indium phosphide quantum dots from indium carboxylates and tris(trimethylsilyl)phosphine (P(SiMe3)3) is understood to proceed through the formation of magic-sized clusters, with In37P20(O2CR)51 being the key isolable intermediate. The reactivity of the In37P20(O2CR)51 cluster is a vital parameter in controlling the conversion to quantum dots. Herein, we report structural perturbations of In37P20(O2CR)51 clusters induced by tuning the steric properties of a series of substituted phenylacetate ligands. This approach allows for control over reactivity with P(SiMe3)3, where meta-substituents enhance the susceptibility to ligand displacement, and para-substituents hinder phosphine diffusion to the core. Thermolysis studies show that with complete cluster dissolution, steric profile can modulate the nucleation period, resulting in a nanocrystal size dependence on ligand steric profile. The enhanced stability from ligand engineering also allows for the isolation and structural characterization by single-crystal X-ray diffraction of a new III-V magic-sized cluster with the formula In26P13(O2CR)39. This intermediate precedes the In37P20(O2CR)51 cluster on the InP QD reaction coordinate. The physical and electronic structure of this cluster are analyzed, providing new insight into previously unrecognized relationships between II-VI and III-V materials and the discrete growth of III-V cluster intermediates.

Current Status and Challenges in Indium Phosphide Quantum Dots and Their Electroluminescence

Current Status and Challenges in Indium Phosphide Quantum Dots and Their Electroluminescence

Growth of Medium-Sized InP Quantum Dots with High Photoluminescence Efficiency and Enhanced Stability

This study introduces medium-sized core/shell InP quantum dots (QDs) with high photoluminescence (PL) efficiency and remarkable material stability. The incorporation of a ZnSe interlayer between the core and the thicker outer ZnS shell enhances both the optical performance and material stability. When further increasing the S/Se ratio to synthesize larger QDs with a thicker ZnS layer, optical performance significantly declines despite the improvement in stability. To achieve QDs with superior optical performance and stability, we controlled the S/Se ratio variation during shell growth and examined its impact on the structure, morphology, and size of InP QDs. Our approach resulted in medium-sized InP/ZnSe/ZnS QDs with tunable wavelengths (606-630 nm), PL quantum yields (PLQY) > 90%, full width at half maximum (FWHM) values < 40 nm, and enhanced material stability.Keywords: indium phosphide (InP), quantum dots (QDs), high efficiency and stability, S/Se ratio of shell, medium-size quantum dots, stainless steel reactor Figure 1

Study of Indium Phosphide Quantum Dots/Carbon Quantum Dots System for Enhanced Photocatalytic Hydrogen Production from Hydrogen Sulfide

Quantum dots (QDs) are promising semiconductor nanocrystals in photocatalysis due to their unique properties and in contrast to bulk semiconductors. Different from the traditional modification methods of indium phosphide (InP) QDs such as metal doping, shell design, and surface ligand modification, we firstly constructed the indium phosphide quantum dot and carbon quantum dot (InP QDs/CQDs) system and used it for the study of photocatalytic hydrogen production from hydrogen sulfide (H2S) in this work. The photocatalytic performance tests show that the average rate of photocatalytic decomposition of hydrogen sulfide to produce hydrogen of the InP QDs/CQDs system increases by 2.1 times in contrast to InP QDs alone. The steady-state and time-resolved photoluminescence spectra demonstrated that the introduction of CQDs can effectively improve the separation efficiency of photo-generated carriers. In addition, the surface electronegativity of the InP QDs/CQDs system is weaker than that of InP QDs, which may reduce the repulsion between the photocatalyst and reaction substrate, promoting the surface oxidation reaction in the photocatalytic process. This work indicates that the construction of the QDs hybrid system can improve their photocatalytic performance, providing a way to optimize QDs in photocatalysis.

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.

Resonance energy transfer in electrostatically assembled donor-acceptor system based on blue-emitting InP quantum dots

Demonstration of light harvesting studies with blue-emitting quantum dots (QDs) is important to expand the scope of QDs in various optoelectronic applications including display, photocatalysis, energy and electron transfer processes, sensing, etc. Here, we report a light induced Förster resonance energy transfer (FRET) process in an all-QD based nanohybrid system containing pure-blue emitting indium phosphide (InP) QDs. A precise control over the kinetics of nucleation and growth processes resulted in the formation of environmentally friendly blue and green emitting InP QDs. The surfaces of the QDs were functionalized with oppositely charged ligands to form an electrostatically assembled donor-acceptor system based on blue and green emitting InP QDs. A large spectral overlap integral and the close proximity between the QDs in the electrostatically assembled donor-acceptor system led to an efficient FRET process (∼65%) from blue-emitting InP QDs to green-emitting InP QDs in water. Systematic steady-state and time-resolved spectroscopic studies revealed the involvement of both static as well as dynamic components in the photoluminescence quenching process. Control experiments conclusively prove the necessity of appropriately functionalized QDs and electrostatic attraction for achieving an efficient FRET process. In short, our work proves the ability of blue-emitting InP QDs to participate in an efficient FRET process, which can accelerate the development of all-QD based light harvesting systems for various optoelectronic applications.