InP-based Quantum Dots Research Articles

Enhancing device characteristics of InP quantum dot LED through structural modification with polyethylene glycol blend

This study explored the integration of polyethylene glycol (PEG) into InP-based quantum dot (QD) light-emitting diodes (LEDs). By 5 wt% of PEG 400 blended into the QD emission layer (EML), we achieved an enhancement in both current efficiency (100 %) and external quantum efficiency (91 %). X-ray reflectivity revealed significant morphological changes in the QD EML upon PEG incorporation, primarily manifesting as increased thickness in the dense surface region without affecting the total thickness. This adjustment influenced electron density distribution, impacting hole and electron flow. Overall, the addition of PEG not only improved the electrical properties of QD LEDs but also reshaped the internal morphology of the QD EML. Notably, the efficiency improvements observed rival those achieved by integrating traditional hole transport materials into QD EMLs.

Enhancing the reliability of InP-based QD color conversion layer through a uniform organic encapsulation layer via inkjet printing

Quantum dot (QD) as a color conversion layer (CCL) is gaining increasing attention for use in next generation displays. However, QD CCL, especially those based on indium phosphide (InP) materials, are vulnerable to oxygen and moisture. Accordingly, even in CCL technology, encapsulation is essential to mitigate performance reduction due to the degradation of color conversion efficiency (CCE). Herein, we employed only acrylic-based resin to produce a uniform encapsulation layer on a CCL, enhancing the CCE reliability of the QD CCL under ambient conditions. To print a uniform encapsulation layer, we confirmed the significance of the minimized surface energy differences on glass, bank, and QD film through O2 plasma treatment. We also investigated coating characteristics through adjustment of the drop spacing to analyze the reliability of the CCL. Compared to the CCL without an encapsulation layer, the CCE only showed a decrease of 1.96 % at green and 3.6 % at red light, after 168 h. The T95 (time to 95 % of the initial luminance) was improved from 5.25 h to 75.02 h by applying the encapsulation layer. As a result, we enhanced the stability of the InP-based QD CCL by printing only an organic encapsulation layer using the inkjet printing process.

Transition Layer Assisted Synthesis of Defect Free Amine-Phosphine Based InP QDs.

Environmentally friendly InP-based quantum dots (QDs) are promising for light-emitting diodes (LEDs) and display applications. So far, the synthesis of highly emitting InP-based QDs via safe and economically viable amine-phosphine remains a challenge. Herein, we report the synthesis of amine-phosphine based InP/ZnSe/ZnS QDs by introducing an alloyed oxidation-free In-ZnSe transition layer (TL) at the core-shell interface. The TL not only has the essential function of preventing oxidation of the core and relieving interfacial strain but also results in oriented epitaxial growth of shell. The alloyed TL significantly mitigates the nonradiative recombination at core-shell interfacial trap states, thereby boosting the photoluminescence (PL) efficiency of the QDs up to 98%. Also, the Auger recombination is suppressed, extending the biexciton lifetime from 60 to 100 ps. The electroluminescence device based on the InP-based QDs shows a high external quantum efficiency over 10%, further demonstrating high quality QDs synthesized by this process.

Encapsulation of InP/ZnS Quantum Dots into MOF-5 Matrices for Solid-State Luminescence: Ship in the Bottle and Bottle around the Ship Methodologies.

The utilization of InP-based quantum dots (QDs) as alternative luminescent nanoparticles to cadmium-based QDs is actively pursued. However, leveraging their luminescence for solid-state applications presents challenges due to the sensitivity of InP QDs to oxidation and aggregation-caused quenching. Hence, an appealing strategy is to protect and disperse InP QDs within hybrid materials. Metal-organic frameworks (MOFs) offer a promising solution as readily available crystalline porous materials. Among these, MOF-5 (composed of {Zn4O}6+ nodes and terephthalate struts) can be synthesized under mild conditions (at room temperature and basic pH), making it compatible with InP QDs. In the present work, luminescent InP/ZnS QDs are successfully incorporated within MOF-5 by two distinct methods. In the bottle around the ship (BAS) approach, the MOF was synthesized around the QDs. Alternatively, in the ship in the bottle (SIB) strategy, the QDs were embedded via capillarity into a specially engineered, more porous variant of MOF-5. Comparative analysis of the BAS and SIB approaches, evaluating factors such as operational simplicity, photoluminescence properties, and the resistance of the final materials to leaching were carried out. This comparative study provides insights into the efficacy of these strategies for the integration of InP/ZnS QDs within MOF-5 for potential solid-state applications in materials chemistry.

Improving spectral linewidth performance of InP quantum dots by promoting size-focused growth and decreasing exciton-phonon coupling

InP-based quantum dots (QDs) are widely adopted as a superior alternative to CdSe-based QDs in various fields owing to their high quantum yield, environmental friendliness, and excellent stability. However, improving its color purity remains a challenging task. In this work, we employ a multistage heating strategy to optimize the nucleation and shell growth processes of amino-phosphine-based InP/ZnSe/ZnS QDs for reducing emission linewidths. The multistage heating strategy mitigates the undesired formation of small-size cores by decreasing monomer supersaturation during the nucleation process, thereby promoting size-focusing growth. During the shelling process, multistage heating effectively suppresses Zn2+ diffusion into the InP core while ensuring high-quality shell growth, thus reducing the homogeneous broadening caused by exciton-phonon coupling. Compared to classical synthesis, the multistage heating strategy can reduce the emission linewidth of nucleation and shelling by 13.2% and 30.9% respectively. The optimized InP/ZnSe/ZnS QDs exhibit a narrow full width at half maximum (FWHM) of 41.5 nm at 630 nm, representing significant progress in studying spectral linewidths of amino-phosphine InP QDs. This work provides potential insights for further improving the spectral linewidth performance of InP QDs or other nanocrystals with similar reaction-limited growth systems.

Construction of Reverse Type-II InP/ZnxCd1-xS Core/Shell Quantum Dots with Low Interface Strain to Enhance Photocatalytic Hydrogen Evolution.

The InP-based quantum dots (QDs) have attracted much attention in the field of photocatalytic H2 evolution. However, a shell should be used for InP-based photocatalytic systems to passivate the numerous surface defects. Different from the traditional InP-based core/shell QDs with Type-I or Type-II band alignment, herein, the "reverse Type-II" core/shell QDs in which both the conduction and valence bands of shell materials are more negative than those of core materials have been well-designed by regulating the ratio of Cd/Zn of the alloyed ZnxCd1-xS shell. The reverse Type-II band alignment would realize the spatial separation of photogenerated carriers. More importantly, the photogenerated holes tend to rest on the shell in the reverse Type-II QDs, which facilitate hole transfer to the surface, the rate-determining step for solar H2 evolution using QDs. Therefore, the obtained InP/Zn0.25Cd0.75S core/shell QDs exhibit superior photocatalytic activity and stability under visible light irradiation. The rate of solar H2 evolution reaches 376.19 μmol h-1 mg-1 at the initial 46 h, with a turnover number of ∼2,157,000 per QD within 70 h irradiation.

Angular Momentum Fine Structure in InP/ZnSe Quantum Dots.

There is a large experimental and theoretical literature on the angular momentum fine structure of the lowest energy exciton in InP-based quantum dots. This literature is highly contradictory, and no clear picture of the fine structure accounting for all these results is available. This paper presents a quantitative analysis of recently published luminescence anisotropy results and presents an analysis of the different proposed fine structure models that compares radiative lifetimes calculated from those models with experimental values. These analyses show that the lowest energy (dark) state is the mj = ±2 state and the lowest energy bright state is a vibronically allowed phonon level. The splittings between the ±2/±1L states and the ±1U/0U states are the same, about 28 meV. We also find that the manifold of J = 1 states is about 60 meV above the manifold of J = 2 states.

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.

Encapsulation of Cadmium-Free InP-based Quantum Dots in Cross-Linked Core-Shell Microparticles via Coaxial Electrospraying.

Quantum dots (QDs) are inorganic semiconductornanocrystalscapable of emitting light. The current major challenge lies in theuseofheavy metals, which are known to be highly toxic to humans and pose significant environmental risks. Researchers have turned to indium (In) as a promising option for more environmentally benign QDs, specifically indium phosphide (InP). A significant obstacle remains in sustaining the long-term photostability of InP-based QDs when exposed to the environment. To tackle this, electrospraying is used in this work to protect indium phosphide/zinc selenide/zinc sulfide (InP/ZnSe/ZnS) QDs by embedding them within polymer core-shell microparticles of poly[(lauryl methacrylate)-co-(ethylene glycol dimethacrylate)]/poly(methyl methacrylate)(poly(LMA-co-EGDMA)/PMMA). During the flight of droplets, the liquid monomer core of LMA and EGDMA with QDs is encapsulated by the solid shell of PMMA formed due to solvent evaporation, resulting in a liquid-core/solid-shell particle structure. After that, the captured core of monomers is polymerized into a cross-linked polymer with the embedded QDs via a thermal initiation. They demonstrate how a successful core-shell particle formation is achieved to produce structures for initially liquid monomer systems via coaxial electrospraying that are used for cross-linked polymers, which are of major interest for the encapsulation of InP-based QDs for generally improved photostability over pristineQDs.

(Invited) Luminescent InP Quantum Dots: They're Not Just Like CdSe

There are significant similarities and differences in the spectroscopy and photophysics between CdSe-based and InP-based quantum dots. One of the more important differences is the presence of reversibly populated hole traps in InP/ZnSe quantum dots (QDs). These traps affect many aspects of the overall excited state dynamics. In this paper we elucidate the hole relaxation dynamics in high quality InP/ZnSe/ZnS QDs at room temperature and focus on the role of these traps. Specifically, we show that the presence of transiently populated traps results in extremely slow (tens of picoseconds to nanoseconds) hole cooling as evidenced by a significant fraction of the photoluminescence exhibiting a slow risetime following photoexcitation. Through a combination of chemical derivatization studies and density functional theory calculations, they are assigned to substitutional indium adjacent to a zinc vacancy, In3+/VZn 2-, in the ZnSe shell.

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.

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.

Highly Sensitive, Stable InP Quantum Dot Fluorescent Probes for Quantitative Immunoassay Through Nanostructure Tailoring and Biotin-Streptavidin Coupling.

Nontoxic, highly sensitive InP quantum dot (QD) fluorescent immunoassay probes are promising biomedical detection modalities due to their unique properties. However, InP-based QDs are prone to surface oxidation, and the stability of InP QD-based probes in biocompatible environments remains a crucial challenge. Although the thick shell can provide some protection during the phase transfer process of hydrophobic QDs, the photoluminescence quantum yield (PLQY) is generally decreased because of the contradiction between lattice stress relaxation and thick shell growth. Herein, we developed thick-shell InP-based core/shell QDs by inserting a ZnSeS alloy layer. The ternary ZnSeS intermediate shell could effectively facilitate lattice stress relaxation and passivate the defect states. The synthesized InP/ZnSe/ZnSeS/ZnS core/alloy shell/shell QDs (CAS-InP QDs) with nanostructure tailoring revealed a larger size, high PLQY (90%), and high optical stability. After amphiphilic polymer encapsulation, the aqueous CAS-InP QDs presented almost constant fluorescence attenuation and stable PL intensity under different temperatures, UV radiation, and pH solutions. The CAS-InP QDs were excellent labels of the fluorescence-linked immunosorbent assay (FLISA) for detecting C-reactive protein (CRP). The biotin-streptavidin (Bio-SA) system was first introduced in the FLISA to further improve the sensitivity, and the CAS-InP QDs-based SA-Bio sandwich FLISA realized the detection of CRP with an impressive limit of detection (LOD) of 0.83 ng/mL. It is believed that the stable and sensitive InP QD fluorescent probes will drive the rapid development of future eco-friendly, cost-effective, and sensitive in vitro diagnostic kits.

The Narrow Synthetic Window for Highly Homogenous InP Quantum Dots toward Narrow Red Emission.

Low-toxicity InP-based quantum dots (QDs) exhibit potential for replacing Cd/Pb-containing QDs in the visible and near-infrared regions. Despite advancements, further improvement relies on synthesizing homogeneous InP QDs to achieve a high color purity. In a commonly employed two-step "seed-mediated" synthetic approach, we demonstrate the high sensitivity of InP seed sizes and size distribution to the quantities of trioctylphosphine (TOP) and tris(trimethylsilyl)phosphine [(TMS)3P], attributed to the process of "self-focusing of size distribution" and enhanced reactivity of In-oleate through coordination with TOP. During growth, the processes of size focusing and defocusing are modulated by the accumulation of oleic acid and TOP molecules, as well as the amount of (TMS)3P in the growth precursor, which may relate to the dissolution process of InP magic size clusters. Through precise control, the best valley/depth ratio of InP QDs was 0.52 at the first absorption peak at 571 nm, resulting in luminescence with a full width at half-maximum of 35 at 620 nm with an absolute photoluminescence quantum yield around 90% after heteroepitaxial growth with ZnSe and ZnS shells.

Polarized and Bright Telecom C-Band Single-Photon Source from InP-Based Quantum Dots Coupled to Elliptical Bragg Gratings.

Bright, polarized, and high-purity single-photon sources in telecom wavelengths are crucial components in long-distance quantum communication, optical quantum computation, and quantum networks. Semiconductor InAs/InP quantum dots (QDs) combined with photonic cavities provide a competitive path, leading to optimal single-photon sources in this range. Here, we demonstrate a bright and polarized single-photon source operating in the telecom C-band based on an elliptical Bragg grating (EBG) cavity. With a significant Purcell enhancement of 5.25 ± 0.05, the device achieves a polarization ratio of 0.986, a single-photon purity of g2(0) = 0.078 ± 0.016, and a single-polarized photon collection efficiency of ∼24% at the first lens (NA = 0.65) without blinking. These findings suggest that C-band QD-based single-photon sources are potential candidates for advancing quantum communication.

Thermally assisted optical processes in InP/ZnS quantum dots.

The utilization of InP-based biocompatible quantum dots (QDs) necessitates a comprehensive understanding of the structure-dependent characteristics influencing their optical behavior. The optimization of core/shell QDs for practical applications is of particular interest due to their reduced toxicity, enhanced photostability, and improved luminescence efficiency. This optimization involves analyzing thermally activated processes involving exciton and defect-related energy levels. This study investigates water-soluble colloidal InP/ZnS QDs with varying shell thicknesses and stabilizing coatings using temperature-dependent optical absorption (OA) and photoluminescence (PL). Our results indicate that all samples experience temperature-induced shifts in exciton absorption and luminescence peaks due to interactions with acoustic phonons. Despite the wide size distribution of nanocrystals, the halfwidth of the bands remains constant. We observe a temperature-dependent Stokes shift in InP/ZnS QDs, revealing the fine structure of exciton states across different configurations. Furthermore, our findings demonstrate common mechanisms underlying PL thermal quenching in these QDs, regardless of the shell thickness or coating type. Specifically, defect-related emissions arise from localized energy levels at the core/shell interface. At the same time, exciton PL quenching primarily occurs through thermally activated electron migration from the InP core to the ZnS shell. Overall, our study highlights the potential for tailoring the temperature response of InP/ZnS QDs by adjusting shell thickness, offering opportunities to optimize their performance for specific applications.

Synthesis of High Efficient InP Based Quantum Dot by Reactivity Control of Zinc Precursors

Synthesis of High Efficient InP Based Quantum Dot by Reactivity Control of Zinc Precursors

InP-based Quantum Dot Solutions for Efficient and Reliable Color Conversion in MicroLED Applications

InP-based Quantum Dot Solutions for Efficient and Reliable Color Conversion in MicroLED Applications

InP-based quantum dot on-chip white LEDs with optimal circadian efficiency

InP-based quantum dot on-chip white LEDs with optimal circadian efficiency

Passivating defects in ZnO electron transport layer for enhancing performance of red InP-based quantum dot light-emitting diodes

ZnO nanoparticles (NPs) are considered the most promising materials for electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs). Herein, we employed a synergistic strategy of Mg doping and ZnMgO shell coating to modify the defect states and energy levels of ZnO NPs. Mg doping mitigated the exciton luminescence quenching caused by charge transfer. A ZnMgO shell was also applied to coat the Mg-doped ZnO (ZMO) NPs to passivate surface oxygen defects further. Consequently, QLEDs utilizing ZMO@ZnMgO ETL demonstrate external quantum efficiency and maximum current efficiency of 9.0 % and 11.5 cd A−1. This work shows an effective defect passivation strategy to enhance the performance of red-emitting InP-based QLEDs.