Beneficial effects of water in the colloidal synthesis of InP/ZnS core-shell quantum dots for optoelectronic applications

Tailoring Red-to-Blue Emission in In1-xGaxP/ZnSe/ZnS Quantum Dots Using a Novel [In(btsa)2Cl]2 Precursor and GaI3

Ternary In1-xGaxP quantum dots (QDs) have emerged as promising materials for efficient blue emission, owing to their tunable bandgap, high stability, and superior optoelectronic properties. However, most reported methods for Ga incorporation into the InP structure have predominantly relied on cation exchange in pre-grown InP QDs at elevated temperatures above 280 °C. This is largely due to the fact that, when heating In and P precursors in the presence of Ga, an InP/GaP core-shell structure readily forms. Herein, we introduce a novel synthesis approach using the indium precursor [In(btsa)2Cl]2 and GaI3 to fabricate In1-xGaxP QDs in a single step at relatively low temperatures (200 °C). By adjusting the GaI3 content, we achieved controlled emission tuning from red to blue. Structural and compositional analysis through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed successful Ga3+ incorporation into the QD core, with a corresponding blue shift in the emission as GaI3 content increased. The synthesized QDs demonstrated a photoluminescence quantum yield (PLQY) of ~50% and a full width at half maximum (FWHM) of 45~62 nm, highlighting the potential of this synthesis method for advanced optoelectronic applications.

Fe─S Bond-Mediated Efficient Electron Transfer in Quantum Dots/Metal-Organic Frameworks for Boosting Photoelectrocatalytic Nitrogen Fixation

Effective electron supply to produce ammonia in photoelectrochemical nitrogen reduction reaction (PEC NRR) remains challenging due to the sluggish multiple proton-coupled electron transfer and unfavorable carrier recombination. Herein, InP quantum dots decorated with sulfur ligands (InP QDs-S2-) bound to MIL-100(Fe) as a benchmark catalyst for PEC NRR is reported. It is found that MIL-100(Fe) can combined with InP QDs-S2- via Fe─S bonds as bridge to facilitate the electron transfer by experimental results. The formation of Fe─S bonds can facilitate electron transfer from inorganic S2- ligands of InP QDs to the Fe metal sites of MIL-100(Fe) within 52 ps, ensuring a more efficient electron transfer and electron-hole separation confirmed by the time-resolved spectroscopy. More importantly, the process of photo-induced carrier transfer can be traced by in situ attenuated total reflection surface-enhanced infrared tests, certifying that the effective electron transfer can promote N≡N dissociation and N2 hydrogenation. As a result, InP QDs-S2-/MIL-100(Fe) exhibits prominent performance with an outstanding NH3 yield of 0.58 µmol cm-2 h-1 (3.09 times higher than that of MIL-100(Fe)). This work reveals an important ultrafast dynamic mechanism for PEC NRR in QDs modified metal-organic frameworks, providing a new guideline for the rational design of efficient MOFs photocathodes.

Narrow-Band Green-Emitting Hybrid Organic-Inorganic Eu (II)-Iodides for Next-Generation Micro-LED Displays

Low-dimensional metal halide perovskites are an emerging class of light-emitting materials for LED-based displays; however, their B-site cations are confined to ns2, d5, and d10 metals. Here, the design of divalent rare earth ions at B-site is presented and a novel Eu(II)-based iodide hybrid is reported with efficient (PLQY ≈98%) narrow-band (FWHM ≈43 nm) green emission and high thermal stability (97%@150 °C). Owing to reduced lattice vibrations and shrunken average distance of Eu(II)-iodide bonds in the face-sharing 1D-structure, photoluminescence from Eu(II) 4f-5d transition appears along with elevated crystal-field splitting of 5d energy level. The Eu(II)-based iodide hybrid is further demonstrated for color-pure green phosphor-converted LEDs with a maximum brightness of ≈396 000 cd m-2 and photoelectric efficiency of 29.2%. High-resolution micrometer-scale light-emitting diode (micro-LED) displays (2540 PPI) via the solution-processed screen is also presented. This work thus showcases a compelling narrow-band green emitter for commercial micro-LED displays.

Synergistic Effect of Halogen Ions and Shelling Temperature on Anion Exchange Induced Interfacial Restructuring for Highly Efficient Blue Emissive InP/ZnS Quantum Dots

InP quantum dots (QDs) have attracted much attention owing to their nontoxic properties and shown great potential in optoelectronic applications. Due to the surface defects and lattice mismatch, the interfacial structure of InP/ZnS QDs plays a significant role in their performance. Herein, the formation of In-S and S_x -In-P_1-x interlayers through anion exchange at the shell-growth stage is revealed. More importantly, it is proposed that the composition of interface is dependent on the synergistic effect of halogen ions and shelling temperature. High shelling temperature contributes to the optical performance improvement resulting from the formation of interlayers, besides the thicker ZnS shell. Moreover, the effect relates to the halogen ions where I^- presents more obvious enhancement than Br^- and Cl^- , owing to their different ability to coordinate with In dangling bonds, which are inclined to form In-S and S_x -In-P_1-x bonds. Further, the anion exchange under I^- -rich environment causes a blue-shift of emission wavelength with shelling temperature increasing, unobserved in a Cl^- - or Br^- -rich environment. It contributes to the preparation of highly efficient blue emissive InP/ZnS QDs with emission wavelength of 473 nm, photoluminescence quantum yield of ≈50% and full width at half maximum of 47 nm.

Chemical synthesis and optical, structural, and surface characterization of InP-In2O3 quantum dots

InP-In₂O₃ colloidal quantum dots (QDs) synthesized by a single-step chemical method without injection of hot precursors (one-pot) were investigated. Specifically, the effect of the tris(trimethylsilyl)phosphine, P(TMS)₃, precursor concentration on the QDs properties was studied to effectively control the size and shape of the samples with a minimum size dispersion. The effect of the P(TMS)₃ precursor concentration on the optical, structural, chemical surface, and electronic properties of InP-In₂O₃ QDs is discussed. The absorption spectra of InP-In₂O₃ colloids, obtained by both UV-Vis spectrophotometry and photoacoustic spectroscopy, showed a red-shift in the high-energy regime as the concentration of the P(TMS)₃ increased. In addition, these results were used to determine the band-gap energy of the InP-In₂O₃ nanoparticles, which changed between 2.0 and 2.9 eV. This was confirmed by Photoluminescence spectroscopy, where a broad-band emission displayed from 2.0 to 2.9 eV is associated with the excitonic transition of the InP and In₂O₃ QDs. In₂O₃ and InP QDs with diameters ranging approximately from 8 to 10 nm and 6 to 9 nm were respectively found by HR-TEM. The formation of the InP and In₂O₃ phases was confirmed by X-ray Photoelectron Spectroscopy.

Chemical synthesis and optical, structural, and surface characterization of InP-In2O3 quantum dots

InP-In₂O₃ colloidal quantum dots (QDs) synthesized by a single-step chemical method without injection of hot precursors (one-pot) were investigated. Specifically, the effect of the tris(trimethylsilyl)phosphine, P(TMS)₃, precursor concentration on the QDs properties was studied to effectively control the size and shape of the samples with a minimum size dispersion. The effect of the P(TMS)₃ precursor concentration on the optical, structural, chemical surface, and electronic properties of InP-In₂O₃ QDs is discussed. The absorption spectra of InP-In₂O₃ colloids, obtained by both UV-Vis spectrophotometry and photoacoustic spectroscopy, showed a red-shift in the high-energy regime as the concentration of the P(TMS)₃ increased. In addition, these results were used to determine the band-gap energy of the InP-In₂O₃ nanoparticles, which changed between 2.0 and 2.9 eV. This was confirmed by Photoluminescence spectroscopy, where a broad-band emission displayed from 2.0 to 2.9 eV is associated with the excitonic transition of the InP and In₂O₃ QDs. In₂O₃ and InP QDs with diameters ranging approximately from 8 to 10 nm and 6 to 9 nm were respectively found by HR-TEM. The formation of the InP and In₂O₃ phases was confirmed by X-ray Photoelectron Spectroscopy.

Narrow-Band SrMgAl10O17:Eu2+, Mn2+ Green Phosphors for Wide-Color-Gamut Backlight for LCD Displays

The strength of the photoluminescence excitation (PLE) spectrum of SrMgAl₁₀O₁₇:Eu²⁺, Mn²⁺ (SAM:Eu²⁺, Mn²⁺) phosphor increased at deep blue (∼430 nm) and red-shifted from violet to deep blue with increasing concentrations of both Eu²⁺ ions Mn²⁺ ions. Eu²⁺-Mn²⁺ energy transfer between Eu²⁺ ions in Sr-O layer and Mn²⁺ ions at Al-O tetrahedral sites was maximized, and the photoluminescence (PL) intensity of the narrow-band Mn²⁺ emission was improved by optimizing the concentrations of Eu²⁺ and Mn²⁺ ions. The PL emission spectrum of the (Sr_0.6Eu_0.4)(Mg_0.4Mn_0.6)Al₁₀O₁₇ (SAM:Eu²⁺, Mn²⁺) phosphor peaks was optimized at 518 nm at a full width at half-maximum (FWHM) of 26 nm under light-emitting diode (LED) excitation at 432 nm LED. The color gamut area of a color-filtered RGB triangle of down-converted white LEDs (DC-WLEDs) incorporated with optimum SAM:Eu²⁺, Mn²⁺ green and K₂SiF₆:Mn⁴⁺ (KSF:Mn⁴⁺) red phosphors is enlarged by 114% relative to that of the NTSC standard system in the CIE 1931 color space. The luminous efficacy of our DC-WLED was measured and found to be ∼92 lm/W at 20 mA. Increased energy transfers between dual activators and red-shifted band-edge and enhanced intensity of PLE spectrum indicate the possibility of developing dual-activated narrow-band green phosphors for wide-color gamut in an LCD backlighting system.

InP Quantum Dots: Synthesis and Lighting Applications

InP quantum dots (QDs) are typical III-V group semiconductor nanocrystals that feature large excitonic Bohr radius and high carrier mobility. The merits of InP QDs include large absorption coefficient, broad color tunability, and low toxicity, which render them promising alternatives to classic Cd/Pb-based QDs for applications in practical settings. Over the past two decades, the advances in wet-chemistry methods have enabled the synthesis of small-sized colloidal InP QDs with the assistance of organic ligands. By proper selection of synthetic protocols and precursor materials coupled with surface passivation, the QYs of InP QDs are pushed to near unity with modest color purity. The state-of-the-art InP QDs with appealing optical and electronic properties have excelled in many applications with the potential for commercialization. This work focuses on the recent development of wet-chemistry protocols and various precursor materials for the synthesis and surface modification of InP QDs. Current methods for constructing light-emitting diodes using novel InP-based QDs are also summarized.

Surface passivation extends single and biexciton lifetimes of InP quantum dots

Indium phosphide quantum dots (InP QDs) are nontoxic nanomaterials with potential applications in photocatalytic and optoelectronic fields. Post-synthetic treatments of InP QDs are known to be essential for improving their photoluminescence quantum efficiencies (PLQEs) and device performances, but the mechanisms remain poorly understood. Herein, by applying ultrafast transient absorption and photoluminescence spectroscopies, we systematically investigate the dynamics of photogenerated carriers in InP QDs and how they are affected by two common passivation methods: HF treatment and the growth of a heterostructure shell (ZnS in this study). The HF treatment is found to improve the PLQE up to 16-20% by removing an intrinsic fast hole trapping channel (τ h,non = 3.4 ± 1 ns) in the untreated InP QDs while having little effect on the band-edge electron decay dynamics (τ e = 26-32 ns). The growth of the ZnS shell, on the other hand, is shown to improve the PLQE up to 35-40% by passivating both electron and hole traps in InP QDs, resulting in both a long-lived band-edge electron (τ e > 120 ns) and slower hole trapping lifetime (τ h,non > 45 ns). Furthermore, both the untreated and the HF-treated InP QDs have short biexciton lifetimes (τ xx ∼ 1.2 ± 0.2 ps). The growth of an ultra-thin ZnS shell (∼0.2 nm), on the other hand, can significantly extend the biexciton lifetime of InP QDs to 20 ± 2 ps, making it a passivation scheme that can improve both the single and multiple exciton lifetimes. Based on these results, we discuss the possible trap-assisted Auger processes in InP QDs, highlighting the particular importance of trap passivation for reducing the Auger recombination loss in InP QDs.

Sustainable quantum dot chemistry: effects of precursor, solvent, and surface chemistry on the synthesis of Zn3P2 nanocrystals

The quest of exploring alternative materials for the replacement of toxic cadmium- and lead-based quantum dots (QDs) is necessary for envisaging a sustainable future but remains highly challenging. Tackling this issue, we present the synthesis of Zn3P2 nanocrystals (NCs) of unprecedented quality. New, reactive zinc precursors yield highly crystalline, colloidally stable particles, exhibiting oxide-free surfaces, size tunability and outstanding optical properties relative to previous reports of zinc phosphide QDs.

Controlling the nucleation process of InP/ZnS quantum dots using zeolite as a nucleation site

A novel synthesis strategy to adjust the emission wavelength of InP/ZnS quantum dots, using zeolite as a quantum dot nucleation template.

High-Performance Hybrid InP QDs/Black Phosphorus Photodetector

Zero-dimensional-two-dimensional (0D-2D) hybrid optoelectronic devices have demonstrated high sensitivity and high performance due to the high absorption coefficient of 0D materials with a tunable detection range and a high carrier transport property of 2D materials. However, the reported 0D-2D hybrid devices employ toxic nanomaterials as sensitizing layers, which can limit the practical applications. In this study, we first fabricated the 0D-2D hybrid photodetector using nontoxic InP quantum dots (QDs) as a light-absorbing layer and black phosphorus (BP) as a transport layer. The surface treatment using 1,2-ethanedithiol and thermal treatment were carried out to remove the surface long ligands of colloidal QDs, which can accelerate the charge injection of the photogenerated carriers through the interfaces between InP QDs and BP. The InP QDs/BP hybrid photodetector demonstrates a high responsivity of 1 × 10⁹ A/W and detectivity of 4.5 × 10¹⁶ Jones at 0.05 μW cm^-2 under 405 nm illumination. The results show that 0D-2D hybrid photodetectors based on III-V semiconducting QD materials can be optimized for high-performance photodetectors.

InP/ZnS quantum dot-based fluorescent probe for directly sensitive and selective detection of horseradish peroxidase

InP/ZnS quantum dot (QD)-based fluorescent probe for directly sensitive and selective detection of horseradish peroxidase (HRP) was reported herein. Fluorescence of InP/ZnS QDs was statically quenched by HRP, due to the ground state complex formation of InP/ZnS QDs with HRP. Such ground state complex formation between InP/ZnS QDs and HRP reduced both the α-helix content and the melting temperature of HRP. Several key factors including InP/ZnS QDs concentration, buffer pH value, ionic strength, reaction temperature, and reaction time those affected the analytical performance of InP/ZnS QDs in HRP determination were investigated thoroughly. Under the optimal conditions, fluorescence intensity of InP/ZnS QDs was linearly decreased with the increasing of HRP concentration during the range of 1.0 × 10^-9 M ∼ 3.0 × 10^-8 M (0.01 U ml^-1 ∼ 0.3 U ml^-1) with the detection limit as low as 1.2 × 10^-10 M (1.2 mU ml^-1). The present method showed excellent selectivity for HRP over some amino acids, nucleotides, and common proteins. This method was utilized to detect HRP in synthetic samples successfully.

Multi-wavelength tailoring of a ZnGa2O4 nanosheet phosphor via defect engineering

The multi-wavelength luminescence tailoring of an individual phosphor free of external dopants is of great interest and technologically important for practical applications. Using ZnGa2O4 nanosheets as a target phosphor, we demonstrate how to artificially control the luminescence wavelength centers and their emission intensities to simultaneously emit ultraviolet/blue, green and red light via a feasible defect engineering strategy. Simple high-temperature annealing of hydrothermally synthesized ZnGa2O4 nanosheets leads to the effective tunability of their emission process to present multi-wavelength luminescence due to the structural distortion and the formation of oxygen vacancies. Controlling the annealing temperature and time can further precisely modulate the wavelengths and their corresponding intensities. It is speculated that the migration of Ga into the [GaO4] tetrahedron and the O vacancy are responsible for the multi-wavelength luminescence of the ZnGa2O4 nanosheet phosphor. Finally, the tentative multi-wavelength luminescence behavior of the ZnGa2O4 nanosheet phosphor via defect engineering is discussed based on a series of evidenced experimental observations of XRD, XPS, HRTEM and CL.

Effective Neural Photostimulation Using Indium-Based Type-II Quantum Dots

Light-induced stimulation of neurons via photoactive surfaces offers rich opportunities for the development of therapeutic methods and high-resolution retinal prosthetic devices. Quantum dots serve as an attractive building block for such surfaces, as they can be easily functionalized to match the biocompatibility and charge transport requirements of cell stimulation. Although indium-based colloidal quantum dots with type-I band alignment have attracted significant attention as a nontoxic alternative to cadmium-based ones, little attention has been paid to their photovoltaic potential as type-II heterostructures. Herein, we demonstrate type-II indium phosphide/zinc oxide core/shell quantum dots that are incorporated into a photoelectrode structure for neural photostimulation. This induces a hyperpolarizing bioelectrical current that triggers the firing of a single neural cell at 4 μW mm^-2, 26-fold lower than the ocular safety limit for continuous exposure to visible light. These findings show that nanomaterials can induce a biocompatible and effective biological junction and can introduce a route in the use of quantum dots in photoelectrode architectures for artificial retinal prostheses.

Stokes-Shift-Engineered Indium Phosphide Quantum Dots for Efficient Luminescent Solar Concentrators

Luminescent solar concentrators (LSCs) show promise because of their potential for low-cost, large-area, and high-efficiency energy harvesting. Stokes shift engineering of luminescent quantum dots (QDs) is a favorable approach to suppress reabsorption losses in LSCs; however, the use of highly toxic heavy metals in QDs constitutes a serious concern for environmental sustainability. Here, we report LSCs based on cadmium-free InP/ZnO core/shell QDs with type-II band alignment that allow for the suppression of reabsorption by Stokes shift engineering. The spectral emission and absorption overlap was controlled by the growth of a ZnO shell on an InP core. At the same time, the ZnO layer also facilitates the photostability of the QDs within the host matrix. We analyzed the optical performance of indium-based LSCs and identified the optical efficiency as 1.45%. The transparency, flexibility, and cadmium-free content of the LSCs hold promise for solar window applications.

Near-complete photoluminescence retention and improved stability of InP quantum dots after silica embedding for their application to on-chip-packaged light-emitting diodes

Silica is the most commonly used oxide encapsulant for passivating fluorescent quantum dots (QDs) against degradable conditions. Such a silica encapsulation has been conventionally implemented via a Stöber or reverse microemulsion process, mostly targeting CdSe-based QDs to date. However, both routes encounter a critical issue of considerable loss in photoluminescence (PL) quantum yield (QY) compared to pristine QDs after silica growth. In this work, we explore the embedment of multishelled InP/ZnSeS/ZnS QDs, whose stability is quite inferior to CdSe counterparts, in a silica matrix by means of a tetramethyl orthosilicate-based, waterless, catalyst-free synthesis. It is revealed that the original QY (80%) of QDs is nearly completely retained in the course of the present silica embedding reaction. The resulting QD–silica composites are then placed in degradable conditions such UV irradiation, high temperature/high humidity, and operation of an on-chip-packaged light-emitting diode (LED) to attest to the efficacy of silica passivation on QD stability. Particularly, the promising results with regard to device efficiency and stability of the on-chip-packaged QD-LED firmly suggest the effectiveness of the present silica embedding strategy in not only maximally retaining QY of QDs but effectively passivating QDs, paving the way for the realization of a highly efficient, robust QD-LED platform.

Silica embedding strategy enabling a nearly full PL retention of the original QY of InP QDs is proposed for the realization of a highly efficient, robust QD-LED platform.

Facile, one-pot and scalable synthesis of highly emissive aqueous-based Ag,Ni:ZnCdS/ZnS core/shell quantum dots with high chemical and optical stability

We report here on a one-pot, mild and low cost aqueous-based synthetic route for the preparation of colloidally stable and highly luminescent dual-doped Ag,Ni:ZnCdS/ZnS core/shell quantum dots (QDs). The pure dopant emission of the Ni-doped core/shell QDs was found to be highly affected by the presence of a second dopant ion (Ag⁺). Results showed that the PL emission intensity increases while its peak position experiences an obvious blue shift with an increase in the content of Ag⁺ ions. Regarding the optical observations, we provide a simple scheme for absorption-recombination processes of the carriers through impurity centers. To obtain optimum conditions with a better emission characteristic, we also study the effect of different reaction parameters, such as refluxing temperature, the pH of the core and shell solution, molar ratio of the dopant ions (Ni:(Zn+Cd) and Ag:(Zn+Cd)), and concentration of the core and shell precursors. Nonetheless, the most effective parameter is the presence of the ZnS shell in a suitable amount to eliminate surface trap states and enhance their emission intensity. It can also improve the bio-compatibility of the prepared QDs by restricting the Cd²⁺ toxic ions inside the core of the QDs. The present suggested route also revealed the remarkable optical and chemical stability of the colloidal QDs which establishes them as a decent kind of nano-scale structure for light emitting applications, especially in biological technologies. The suggested process also has the potential to be scaled-up while maintaining the emission characteristics and structural quality necessary for industrial applications in optoelectronic devices.

The role of water in the synthesis of indium nanoparticles

We report the water-assisted synthesis of indium nanoparticles (In NPs). We found that a precise amount of water was necessary to allow the formation of the desired 7 nm In NPs: the oxidation of the In surface by water inhibits the growth of NPs as well as subsequent reactivity with white phosphorus (P₄). A novel surface activation method based on the use of organosilanes is presented.