Tailored Environment-Friendly Reverse Type-I Colloidal Quantum Dots for a Near-Infrared Optical Synapse and Artificial Vision System

Colloidal quantum dots (QDs) are emerging as potential candidates for constructing near-infrared (NIR) photodetectors (PDs) and artificial optoelectronic synapses due to solution processability and a tunable bandgap. However, most of the current NIR QDs-optoelectronic devices are still fabricated using QDs with incorporated harmful heavy metals of lead (Pb) and mercury (Hg), showing potential health and environment risks. In this work, we tailored eco-friendly reverse type-I ZnSe/InP QDs by copper (Cu) doping and extended the photoresponse from the visible to NIR region. Transient absorption spectroscopy analysis revealed the presence of Cu dopant states in ZnSe/InP:Cu QDs that facilitated the extraction of photogenerated charge carriers, leading to an enhanced photodetection performance. Specifically, under 400 nm illumination, the Cu-doped ZnSe/InP QDs-based PDs presented a broadband photodetection ranging from ultraviolet (UV) to NIR, with a responsivity of 70.5 A W-1 and detectivity of 2.8 × 1011 Jones, surpassing those of the undoped ZnSe/InP QDs-based PDs (49.4 A W-1 and 1.9 × 1011 Jones, respectively). More importantly, the ZnSe/InP:Cu QDs-PDs demonstrated various synapse-like characteristics of short-term plasticity (STP), long-term plasticity (LTP), and learning-forging-relearning under NIR light illumination, which were further used to construct PD array devices for simulating the artificial visual system that is available in prospective optical neuromorphic applications.

Aqueous Grown Quantum Dots with Robust Near-Infrared Fluorescence for Integrated Traumatic Brain Injury Diagnosis and Surgical Monitoring

Surgical intervention is the most common first-line treatment for severe traumatic brain injuries (TBIs) associated with high intracranial pressure, while the complexity of these surgical procedures often results in complications. Surgeons often struggle to comprehensively evaluate the TBI status, making it difficult to select the optimal intervention strategy. Here, we introduce a fluorescence imaging-based technology that uses high-quality silver indium selenide-based quantum dots (QDs) for integrated TBI diagnosis and surgical guidance. These engineered, poly(ethylene glycol)-capped QDs emit in the near-infrared region, are resistant to phagocytosis, and importantly, are ultrastable after the epitaxial growth of an aluminum-doped zinc sulfide shell in the aqueous phase that renders the QDs resistant to long-term light irradiation and complex physiological environments. We found that intravenous injection of QDs enabled both the precise diagnosis of TBI in a mouse model and, more importantly, the comprehensive evaluation of the TBI status before, during, and after an operation to distinguish intracranial from superficial hemorrhages, provide real-time monitoring of the secondary hemorrhage, and guide the decision making on the evacuation of intracranial hematomas. This QD-based diagnostic and monitoring system could ultimately complement existing clinical tools for treating TBI, which may help surgeons improve patient outcomes and avoid unnecessary procedures.

Effect of Lattice Disorder on Exciton Dynamics in Copper-Doped InP/ZnSexS1-x Core/Shell Quantum Dots

InP/ZnSexS1-x core/shell quantum dots (QDs) with varying Cu concentrations were synthesized by a one-pot hot-injection method. X-ray diffraction and high-resolution transmission electron microscopy results indicate that Cu doping did not alter the crystal structure or particle size of the QDs. The optical shifts in UV-visible absorption and photoluminescence (PL) suggest changes in the electronic structure and induction of lattice disorder due to Cu doping. Ultrafast transient absorption spectroscopy (TAS) reveled that a higher Cu-doping level leads to faster charge carrier recombination, likely due to increased nonradiative decay from defect states. Time-resolved PL (TRPL) studies show longer average lifetimes of charge carriers with increased Cu doping. These findings informed the development of a kinetic model to better understand how Cu-induced disorder affects charge carrier dynamics in the QDs, which is important for emerging applications of Cu-doped InP/ZnSexS1-x QDs in optoelectronics.

Control of the Reaction Kinetics of Monodispersed InP/ZnSeS/ZnS-Based Quantum Dots Using Organophosphorus Compounds for Electroluminescent Devices

Green emissive InP-based quantum dots (QDs) remain less developed than red QDs because of the difficulty of controlling the reactivity of small InP cores. Herein, we report the synthesis of monodispersed green InP-based QDs using tris(dimethylamino)phosphine, a considerably inexpensive and safer phosphorus source compared to conventional tris(trimethylsilyl)phosphine. An organophosphorus compound, trioctylphosphine, was used to control the reaction kinetics by slowing the progression of the nucleation process, which weakened the aggregation behavior of the clusters and improved the size distribution. The synthesized green emissive InP/ZnSeS/ZnS QDs exhibited a photoluminescence (PL) peak at 515 nm with an enhancement of the full width at half-maximum from 66 to 46 nm and the PL quantum yield from 61% to 70%. An electroluminescent device was fabricated, and the electron transport layer was optimized by changing the layer thickness. The optimized device structure improved the charge balance and increased the external quantum efficiency from 2.1% to 3.5%.

A Novel Strategy to Enhance the Photostability of InP/ZnSe/ZnS Quantum Dots with Zr Doping

Plentiful research of InP semiconductor quantum dots (QDs) has been launched over the past few decades for their excellent photoluminescence properties and environmentally friendly characteristics in various applications. However, InP QDs show inferior photostability because they are extremely sensitive to the ambient environment. In this study, we propose a novel method to enhance the photostability of InP/ZnSe/ZnS QDs by doping zirconium into the ZnS layer. We certify that Zr can be oxidized to Zr oxides, which can prevent the QDs from suffering oxidation during light irradiation. The InP/ZnSe/ZnS:Zr QDs maintained 78% of the original photoluminescence quantum yields without significant photodegradation under the irradiation of LED light (450 nm, 3.0 W power intensity) for 14 h, while conventional InP/ZnSe/ZnS QDs dramatically decreased to 29%.

Passivation and Interlayer Effect of Zr(i-PrO)4 on Green CuGaS2/ZnS/Zr(i-PrO)4@Al2O3 and Red CuInS2/ZnS/Zr(i-PrO)4@Al2O3 QD Hybrid Powders

Broadband emissive I-III-VI quantum dots (QDs) are synthesized as efficient and stable I-III-VI QDs to be used as eco-friendly luminescent materials in various applications. Here, we introduce the additional passivation of zirconium isopropoxide (Zr(i-PrO)₄) to improve the optical properties and environmental stability of green-emitting CuGaS₂/ZnS (G-CGS/ZnS) and red-emitting CuInS₂/ZnS (R-CIS/ZnS) QDs. The photoluminescence quantum yield (PLQY) of both resultant Zr(i-PrO)₄-coated G-CGS/ZnS and R-CIS/ZnS QDs reaches similar values of ~ 95%. In addition, the photostability and thermal-stability of G-CGS/ZnS/Zr(i-PrO)₄ and R-CIS/ZnS/Zr(i-PrO)₄ QDs are improved by reducing the ligand loss via encapsulation of the ligand-coated QD surface with Zr(i-PrO)₄. It is also proved that the Zr(i-PrO)₄-passivated interlayer mitigates the further degradation of I-III-V QDs from ligand loss even under harsh conditions during additional hydrolysis reaction of aluminum tri-sec-butoxide (Al(sec-BuO)₃), forming easy-to-handle G-CGS/ZnS and R-CIS/ZnS QD-embedded Al₂O₃ powders. Therefore, the introduction of a Zr(i-PrO)₄ complex layer potentially provides a strong interlayer to mitigate degradation of I-III-VI QD-embedded Al₂O₃ hybrid powders as well as passivation layer for protecting I-III-VI QD.

A review on I-III-VI ternary quantum dots for fluorescence detection of heavy metals ions in water: optical properties, synthesis and application

Heavy metal contamination remains a major threat to the environment. Evaluating the concentrations of heavy metals in water environments is a crucial step towards a viable treatment strategy. Non-cadmium photo-luminescent I-III-VI ternary QDs have attracted increasing attention due to their low toxicity and extraordinary optical properties, which have made them popular in biological applications. Recently, ternary I-III-VI-QDs have gained growing interest as fluorescent detectors of heavy metal ions in water. Here, we review the research progress of ternary I-III-VI QDs for the fluorescence detection of heavy metal ions in water. First, we summarize the optical properties and synthesis methodologies of ternary I-III-VI QDs. Then, we present various detection mechanisms involved in the fluorescence detection of heavy metal ions, which are mostly attributed to direct interaction between these unique QDs and the metal ions, seen in the form of fluorescence quenching and fluorescence enhancement. We also display the potential applications in environmental remediation such as water treatment and associated challenges of I-III-VI QDs in the fluorescence detection of Cu2+ and other metal ions.

Recent research on the luminous mechanism, synthetic strategies, and applications of CuInS2 quantum dots

We discuss the synthesis and luminescence mechanisms of CuInS₂ QDs, the strategies to improve their luminous performance and their potential application in light-emitting devices, solar energy conversion, and the biomedical field.

Composition-tailored ZnMgO nanoparticles for electron transport layers of highly efficient and bright InP-based quantum dot light emitting diodes

Tailored-ZnMgO layers result in green-emitting InP based quantum dot light emitting diodes (QLEDs) with a maximum luminance of 13 900 cd m-2 and an external quantum efficiency (EQE) of 13.6%. This is the first report of green-emitting InP based QLEDs that exceed an EQE of 10% and a luminance of 13 000 cd m-2.

Electrospun Fibers Containing Emissive Hybrid Perovskite Quantum Dots

We demonstrate a single-step fabrication process of highly stable and luminescent polymer fibers embedded with quantum dots (QDs) of the organic-inorganic hybrid perovskite (OIP) (CH₃NH₃PbBr₃) using the electrospinning process. The fiber (∼2 μm diameter) primarily consists of poly(methyl methacrylate) dispersed with clusters of OIP quantum dots. The OIP clusters are radially distributed, normal to the fiber axis. The photoluminescence quantum yield (PLQY) is high (∼80%) and comparable to that of conventional QDs. The emission maxima are tunable by varying the concentration of OIP precursor in the electrospinning solution. Submicron emission maps show an isotropic and continuous emission along the fiber, suggesting uniform distribution of QD clusters. Temperature-dependent PL response indicates features which are a function of the particle size. For small QDs, the PLQY(T) maxima are close to the ambient temperature, whereas the PLQY(T) maxima shift sizably to T < 50 K for larger QDs. Significant waveguiding of QDs emission and amplified spontaneous emission, a prerequisite for lasing, were observed in the fiber confined OIP system at room temperature.

Al atomistic surface modulation on colloidal gradient quantum dots for high-brightness and stable light-emitting devices

Quantum-dot (QD) light-emitting devices (QLEDs) have been attracting considerable attention owing to the unique properties of process, which can control the emission wavelength by controlling the particle size, narrow emission bandwidth, and high brightness. Although there have been rapid advances in terms of luminance and efficiency improvements, the long-term device stability is limited by the low chemical stability and photostability of the QDs against moisture and air. In this study, we report a simple method, which can for enhance the long-term stability of QLEDs against oxidation by inserting Al into the shells of CdSe/ZnS QDs. The Al coated on the ZnS shell of QDs act as a protective layer with Al₂O₃ owing to photo-oxidation, which can prevents the photodegradation of QD with prolonged irradiation and stabilize the device during a long-term operation. The QLEDs fabricated using CdSe/ZnS/Al QDs exhibited a maximum luminance of 57,580 cd/m² and current efficiency of 5.8 cd/A, which are significantly more than 1.6 times greater than that of CdSe/ZnS QDs. Moreover, the lifetimes of the CdSe/ZnS/Al-QD-based QLEDs were significantly improved owing to the self-passivation at the QD surfaces.

A high-efficiency and stable cupric oxide photocathode coupled with Al surface plasmon resonance and Al2O3 self-passivation

A high-efficiency and stable CuO/Al/Al₂O₃ photocathode for photoelectrochemical water splitting has been successfully synthesized by a facile magnetron sputtering combined with spontaneous oxidation method.

Effect of surface/interfacial defects on photo-stability of thick-shell CdZnSeS/ZnS quantum dots

High color-purity CdZnSeS alloy cores and CdZnSeS/ZnS core/shell quantum dots (QDs) with 3, 11 and 17 monolayer (ML) ZnS shells are synthesized, and the narrow emission (full-width at half-maximum: ∼21 nm) is ascribed to the high size uniformity of QDs and the narrow linewidth of single QD spectra. Ultraviolet (UV) irradiation experiments show that the photo-stabilities of the samples improve remarkably with increasing shell thickness, but the photo-stability clearly decreases when the shell thickness is further increased to 17 MLs. Spectroelectrochemical (SEC) measurements indicate that the exciton recombination of QDs is mainly affected by surface electronic traps, and the interaction between exciton recombination centers and surface traps is significantly weakened with the increase in shell thickness due to the decreased wave function overlap of the exciton and surface traps. In the case of the 17 ML shell, the reduced photo-stability is due to increased interfacial defects caused by stress release during UV illumination, which can be proved by high-resolution transmission electron microscopy images and X-ray diffraction patterns. Furthermore, based on QDs' theoretical mass calculations, a photo-stable white light-emitting diode is fabricated by encapsulating with a thick-shell QD, and an exceptional color gamut of 130% relative to the National Television Systems Committee color space can be achieved. Also, its colorimetry and photometry are discussed in detail.

Stable and Flexible CuInS2/ZnS:Al-TiO2 Film for Solar-Light-Driven Photodegradation of Soil Fumigant

Semiconductor quantum dots (QDs) are suitable light absorbers for photocatalysis because of their unique properties. However, QDs generally suffer from poor photochemical stability against air, limiting their applications in photocatalysis. In this study, a stable solar-light-driven QDs-containing photocatalytic film was developed to facilitate photocatalytic degradation of the soil fumigant 1,3-dichloropropene (1,3-D). Highly stable CuInS2/ZnS:Al core/shell QDs (CIS/ZnS:Al QDs) were synthesized by doping Al into the ZnS shell and controlling ZnS:Al shell thickness; the CIS/ZnS:Al QDs were subsequently combined with TiO2 to form a CIS/ZnS:Al-TiO2 photocatalyst. The optimized ZnS:Al shell thickness for 1,3-D photodegradation was approximately 1.3 nm, which guaranteed and balanced the good photocatalytic activity and stability of the CIS/ZnS:Al-TiO2 photocatalyst. The photodegradation efficiency of 1,3-D can be maintained up to more than 80% after five cycles during recycling experiment. When CIS/ZnS:Al-TiO2 was deposited as photocatalytic film on a flexible polyethylene terephthalate substrate, over 99% of cis-1,3-D and 98% of trans-1,3-D were depleted as they passed through the film during 15 h of irradiation under natural solar light. This study demonstrated that the stable CIS/ZnS:Al-TiO2 photocatalyst both in powder and film form is a promising agent for photodegradation and emission reduction of soil fumigants.

Optoelectronic Properties of CuInS2 Nanocrystals and Their Origin

The capacity of fluorescent colloidal semiconductor nanocrystals for commercial application has led to the development of nanocrystals with nontoxic constituent elements as replacements for the currently available Cd- and Pb-containing systems. CuInS2 is a good candidate material because of its direct band gap in the near-infrared spectral region and large optical absorption coefficient. The ternary nature, flexible stoichiometry, and different crystal structures of CuInS2 lead to a range of optoelectronic properties, which have been challenging to elucidate. In this Perspective, the optoelectronic properties of CuInS2 nanocrystals are described and what is known of their origin is discussed. We begin with an overview of their synthesis, structure, and mechanism of formation. A complete discussion of the tunable luminescence properties and the radiative decay mechanism of this system is then presented. Finally, progress toward application of these "green" nanocrystals is summarized.

Optimized synthesis of CuInS2/ZnS:Al–TiO2 nanocomposites for 1,3-dichloropropene photodegradation

CuInS₂/ZnS:Al–TiO₂ nanocomposites were optimally prepared by response surface methodology and could be highly efficient for soil fumigant photodegradation.