Inorganic Quantum Dots Research Articles

A novel in-situ process for high performance blue CsPbBr3 perovskite quantum dots via Cs ion-exchange in Sodium Titanium Silicate

Inorganic perovskite quantum dots (QDs) have attracted extensive attention from researchers in recent years, because of their good prospects in micro-LED for next generation lighting and display. However, the research on high quality and stable inorganic perovskite blue QDs is relatively backward, which limits its further applications in micro-LED. In the present work, crystalline silicotitanate (CST) is used as matrix and synthesized by hydrothermal method, then, Cs+ ion replaces Na+ ion in the tunnel in c-axis dimension of CST matrix by ion exchange, and finally, the CsPbBr3 QDs are in situ anchored on the Cs+ ion in the tunnel. The sizes of the as prepared CsPbBr3 QDs are determined to be mostly less than 4 nm, which guarantees the as prepared CST: CsPbBr3 QDs to have a brilliant blue emission peak at 463 nm with a narrow FWHM of less than 20 nm, and it can be excited by a broad n-UV light range from 300 to 400 nm and peak at 365 nm. A photoluminescent quantum yield of 88.34% is achieved. Furthermore, the as prepared CST: CsPbBr3 QDs is demonstrated to have a good air and thermal stability with an average PL lifetime of 112.00 ns? The color gamut of CST: CsPbBr3 QDS together with the commercial green (Sr, Ba)2SiO4: Eu2+ and red (Sr, Ca)AlSiN3: Eu2+ phosphors is calculated to be 114.12% of the NTSC standard. Therefore, the present pure blue CST: CsPbBr3 QDs can be a potential backlight source for display devices.

Self‐Driven Multistep Quantum Dot Synthesis Enabled by Autonomous Robotic Experimentation in Flow

Identifying the optimal formulation of emerging inorganic lead halide perovskite quantum dots (LHP QDs) with their vast colloidal synthesis universe and multiple synthesis/postsynthesis processing parameters is a challenging undertaking for material‐ and time‐intensive, batch synthesis strategies. Herein, a modular microfluidic synthesis strategy, integrated with an artificial intelligence (AI)‐guided decision‐making agent for intelligent navigation through the complex colloidal synthesis universe of LHP QDs with 10 individually controlled synthesis parameters and an accessible parameter space exceeding 2 × 107, is introduced. Utilizing the developed autonomous microfluidic experimentation strategy within a global learning framework, the optimal formulation of LHP QDs is rapidly identified through a two‐step colloidal synthesis and postsynthesis halide exchange reaction, for 10 different emission colors in less than 40 min per desired peak emission energy. Using two in‐series microfluidic reactors enables continuous bandgap engineering of LHP QDs via in‐line halide exchange reactions without the need for an intermediate washing step. Using an inert gas within a three‐phase flow format enables successful, self‐synchronized continuous delivery of halide salt precursor into moving droplets containing LHP QDs, resulting in accelerated closed‐loop formulation optimization and end‐to‐end continuous manufacturing of LHP QDs with desired optoelectronic properties.

Multiscale modeling and optimal operation of millifluidic synthesis of perovskite quantum dots: Towards size-controlled continuous manufacturing

Inorganic lead halide perovskite quantum dots (QDs) have emerged as a promising semiconducting nanomaterial candidate for widespread applications, including next-generation solar cells, displays, and photocatalysts. The optoelectronic properties of colloidal QDs are majorly dictated by their bandgap energy (related to their size). Thus, it is important to fine-tune the size while having fast and continuous production of QDs. However, the mass and heat transfer limitations of batch reactors with batch-to-batch variations have hindered precise control over the size-dependent optoelectronic properties of QDs. Thus, to address this knowledge gap, we propose a multiscale model for continuous flow manufacturing of colloidal perovskite QDs. Specifically, a first-principled kinetic Monte Carlo model is integrated with a continuum model to describe a plug-flow crystallizer (PFC). The PFC has two manipulated inputs, precursor concentration and superficial flow velocity, to fine-tune the size of QDs. Furthermore, a neural network based surrogate model is designed to identify an optimal input trajectory which will ensure that the desired QD size is achieved, thereby taking a step towards controlled and reliable nanomanufacturing of QDs.

A Study on an Organic Semiconductor-Based Indirect X-ray Detector with Cd-Free QDs for Sensitivity Improvement.

In this paper, we studied the optimized conditions for adding inorganic quantum dots (QD) to the P3HT:PC70BM organic active layer to increase the sensitivity of the indirect X-ray detector. Commonly used QDs are composed of hazardous substances with environmental problems, so indium phosphide (InP) QDs were selected as the electron acceptor in this experiment. Among the three different sizes of InP QDs (4, 8, and 12 nm in diameter), the detector with 4 nm InP QDs showed the highest sensitivity, of 2.01 mA/Gy·cm2. To further improve the sensitivity, the QDs were fixed to 4 nm in diameter and then the amount of QDs added to the organic active layer was changed from 0 to 5 mg. The highest sensitivity, of 2.26 mA/Gy·cm2, was obtained from the detector with a P3HT:PC70BM:InP QDs (1 mg) active layer. In addition, the highest mobility, of 1.69 × 10−5 cm2/V·s, was obtained from the same detector. Compared to the detector with the pristine P3HT:PC70BM active layer, the detector with a P3HT:PC70BM:InP QDs (1 mg) active layer had sensitivity that was 61.87% higher. The cut-off frequency of the P3HT:PC70BM detector was 21.54 kHz, and that of the P3HT:PC70BM:InP QDs (1 mg) detector was 26.33 kHz, which was improved by 22.24%.

Inorganic Semiconductor Quantum Dots as a Saturated Excitation (SAX) Probe for Sub‐Diffraction Imaging

AbstractThe photoluminescence (PL) saturation of CdSe/ZnS core/shell inorganic semiconductor quantum dots (QDs) and its utility as a probe for saturated excitation (SAX) microscopy are reported. Under saturating excitation power densities, the PL signal was demodulated and recorded at harmonics of the fundamental frequency. For commercially available Qdot® 655 ITK™ QDs, the power density required to achieve saturation was dependent upon the local environment of the QDs. For QDs deposited and dried on a glass substrate, the excitation power density required for PL saturation was less than 1 kW/cm2. Compared to this, saturation of PL for QDs dispersed in water required an excitation power density greater than 200 kW/cm2. This observation is manifested as a limitation in the imaging of hydrated samples, as demonstrated for HeLa cells labelled with biotinylated‐phalloidin followed by labelling with streptavidin‐coated QDs. As saturation affects the obtained spatial resolution in several imaging formats, including confocal imaging, the provided data will aid in obtaining the optimal spatial resolution when using QD probes to image biological samples.

Growing Perovskite Quantum Dots on Carbon Nanotubes for Neuromorphic Optoelectronic Computing

AbstractBrain‐inspired (neuromorphic) computing that offers lower energy consumption and parallelism (simultaneous processing and memorizing) compared to von Neumann computing provides excellent opportunities in many computational tasks ranging from image recognition to speech processing. To accomplish neuromorphic computing, highly efficient optoelectronic synapses, which can be the building blocks of optoelectronic neuromorphic computers, are necessary. Currently, carbon nanotubes (CNTs), an attractive candidate to develop circuit‐level photonic synapses, provide weak light responses. The inferior photoresponse of CNTs increases the energy consumption of neuromorphic optoelectronic devices. Herein, a method to grow organic–inorganic halide perovskite quantum dots (PQDs) directly on multiwall CNTs (MWCNTs) to increase the photosensitivity of optoelectronic synapses is demonstrated. The new hybrid material synchronizes the high photoresponse of PQDs and the excellent electrical properties of MWCNTs to provide photonic memory under very low light intensity (125 µW cm−2). However, neat MWCNTs do not show any detectable light response at the tested light intensity, as high as 25 mW cm−2. Since the PQDs are grown directly on and in the MWCNTs, the hybrid PQD‐MWCNT provides a new direction for the future MWCNT‐based optoelectronic devices for neuromorphic computing with a potential to break the von Neumann bottleneck.

Multiple Cations Enhanced Defect Passivation of Blue Perovskite Quantum Dots Enabling Efficient Light‐Emitting Diodes

AbstractAll inorganic perovskite quantum dots (ABX3, A = Cs, B = Pb, X = Cl, Br, or I) are potential candidates for wide‐color‐gamut display applications. High‐efficiency green and red perovskite quantum dot (PeQD) light‐emitting diodes (LEDs) have been achieved, however, development of blue‐emitting devices, especially those with the relatively short wavelengths (<470 nm) meeting National Television System Committee blue standard, lag largely behind, mainly due to poor film quality, low photoluminescence quantum yield (PLQY) of PeQDs, and unfavorable device structure. Here, a strategy of co‐doping Rb+ and Ni2+ in (Cs0.8Rb0.2)(Pb0.95Ni0.05)(Br1.8Cl1.2) PeQDs is reported to improve the film quality and PLQY of PeQDs by realizing multiple passivations and modifying the energy band of PeQDs to reduce the hole injection barrier. With further engineering the device structure to facilitate the hole transport, PeQDLEDs based on multiple‐cation PeQDs show the maximum EQE of 2.14% and the emission peak at 467 nm with a full width at half maximum of 16 nm. This work would open up a new avenue to design and develop efficient blue‐emitting materials for high‐performance blue PeQDLEDs.

Photo‐ and Magnetothermally Responsive Nanomaterials for Therapy, Controlled Drug Delivery and Imaging Applications

AbstractHyperthermia generates heat as a cure for illness and it is not a chemical treatment. Nanomaterials are supposed to provide novel mechanisms to tackle photothermal and magnetothermal problems, with the potential also to deal with specific approaches to care. The present review outlines recent developments in the field of photothermal and magnetothermal responsive nanomaterials and the photothermal approach mechanism over the last years. These photo/magnetothermal nanomaterials are classified into gold nanostructures (various shapes), carbon nanomaterials (CNTs, fullerene, carbon quantum dots, and graphene), inorganic nanomaterials (Fe, Pt, Pd, Bi, MOF, MoSe2, inorganic quantum dots, etc.) and organic nanoparticles (PLGA (Poly Lactic‐co‐Glycolic Acid) and other nanopolymers). Different groups may be placed together to improve the potential of the photothermal/magnetothermal effects, treatments, drug delivery, and imaging. The review also describes synthesis strategies for photothermal/magnetothermal nanomaterials, physicochemical characterization, the role of size, size distribution, shape, and surface coating of nanomaterials, challenges, and future scopes of photothermal/magnetothermal responsive nanomaterials for therapy, controlled drug delivery, and imaging applications. The recent development in nanomaterial has shown great potential for tumor diagnostic and therapeutic applications in hyperthermia. Magnetic hyperthermia (also called thermal therapy or thermotherapy) is a type of cancer treatment in which body tissue is exposed to high temperatures (up to 41 °C) in presence of a magnetic field. Research has shown that high temperatures can damage and kill cancer cells, usually with minimal injury to normal tissues. By killing cancer cells and damaging proteins and structures within cells, hyperthermia can necrotize tumor cells. This treatment can be local, regional, or whole‐body hyperthermia, depending on the extent of the area being treated. Hyperthermia can be combined with anticancer drugs or chemotherapy to enhance cancer treatment. In this article, we have discussed recent nanomaterials utilized for this treatment, mechanism, and synthesis methods.

Enhanced Spatial Light Confinement of All Inorganic Perovskite Photodetectors Based on Hybrid Plasmonic Nanostructures.

3D incident light confinement by radical electromagnetic fields offers a facile and novel way to break through the performance limit of inorganic perovskite CsPbBr3 quantum dots (QDs). Herein, metallic nanoparticles decorated anodic aluminum oxide (AAO) hybrid plasmonic nanostructures with geometric control are first proposed for cyclic light utilization of perovskite photodetectors, enabled by spatially extended light confinement. The drastic multiple interference induced by plasmonic coupling within AAO matrixes are generated as a function of pore sizes, which can effectively collect the transmitted photons back to the surface. In addition, the self-assembled metallic nanoparticles simultaneously concentrate the incident and reflected light beams into the CsPbBr3 QD layers. The light confinement inherently stems from the metallic nanoparticles due to the variation of the near surface electromagnetic fields. As a result, perovskite photodetectors based on Al nanoparticles/AAO hybrid plasmonic nanostructures with a pore size of 220nm exhibit enhanced photoresponse behavior with remarkably increased photocurrent by ≈43× and maintain low dark current under 490nm light illumination at 1V.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges.

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Sustainable synthesis of carbon dots from agarose waste and prospective application in sensing of l-aspartic acid

The excessive utilization of carbon dots (CDs) has led to different fates and perseverance which further prejudiced by various photochemical and other transformations. The mechanistic behaviour of their respective conversions is still very unclear. The present report fulfils this knowledge breach by single step synthesis of CDs with one step synthesis of CDs by thermal treatment by using agarose waste. The formed particles have possessed outstanding quantum yield with value ∼ 62 %. The developed CDs are highly sustainable and non-toxic in nature as compared to organic and inorganic quantum dots as their unknown chemical, physical and optoelectronic properties limit their widespread use. The exceptional luminescence and physicochemical characteristics of developed CDs inspired this research work towards commercial products. With this view, they particles have been successfully applied in recognition of biological component such as aspartic acid. The fluorescence emission intensity of developed CDs reflects extraordinary sensitivity and selectivity towards l-aspartic acid out of twenty amino acids through quenching mechanism in wide concentration range with a linear relationship of 10 μm to 1 nm and value of detection limit was found to be 0.28 nm. Astonishingly, such a sensor can be applied in real world analysis with satisfactory spiked recovery of 98 %. The developed C-dots are pragmatic to real sample recognition and results are highly sustaining.

Recent Progress in Emerging Near-Infrared Emitting Materials for Light-Emitting Diode Applications

In view of the wide applications of near-infrared (NIR) light in night vision, security, medicine, sensors, telecommunications, and military applications, and the scarcity of high-efficiency NIR-emitting materials, development of alternative NIR-emitting materials is urgently required. In this review, we focus on three kinds of emerging NIR-emitting materials used in light-emitting diodes (LEDs), namely organic materials, inorganic quantum dot (QD) materials, and organic–inorganic hybrid perovskite materials; the corresponding devices are organic LEDs, QD LEDs, and perovskite LEDs. The advantages and disadvantages of the three kinds of materials are discussed, some representative works are reviewed, and a brief outlook for these materials is provided.

Superradiant emission from self-assembled light emitters: From molecules to quantum dots

Abstract

The Elusive Nature of Carbon Nanodot Fluorescence: An Unconventional Perspective

The burgeoning interest raised by carbon dots (CDs) is an epitome of the urgency to develop green and biocompatible alternatives to inorganic and hybrid quantum dots. The fast-paced development of synthetic approaches for CDs over the past few years has left many open questions on their characterization. Herein, we further confirm how the standardization of CDs cannot disregard the presence of fluorescent molecular byproducts. On the contrary, we show how the emissive properties of our solvothermally synthesized CDs largely stem from free molecular adducts produced during the synthesis of carbon cores. The presence of these small molecules, not detectable by electron microscopy, could be deceptive for a reliable characterization of the CDs and could lead to an overestimate of their optical properties. Hence, we propose to introduce more bias-free structure–property correlations based on spectroscopy techniques capable of giving direct insights into their structural properties. Through a combination of standard and unconventional characterization techniques, such as fluorescence correlation spectroscopy (FCS) and time-resolved electron paramagnetic resonance (TREPR), we demonstrate how molecular byproducts dominate the emission properties: these are freely moving in the solution rather than decorating a carbonaceous scaffold. Considering carefully the possibility that newly synthesized CDs are heterogeneous solutions will boost the research and optimization of CDs, thereby paving the way to the large-scale production of cheap and biocompatible light-emissive nanostructures.

Water-Stable and Photoelectrochemically Active CsPbBr3/Polyaniline Composite by a Photocatalytic Polymerization Process

Inorganic perovskite quantum dots (PQDs) have emerged as an unprecedented class of optoelectronic materials due to their notable properties. However, their inherent poor stability has become the ma...

Facile synthesis of highly fluorescent water-soluble SnS2 QDs for effective detection of Fe3+ and unveiling its fluorescence quenching mechanism

Abstract In recent years, inorganic semiconductor quantum dots (QDs) have garnered significant attention of scientific diaspora owing to their unique photophysical properties. In this series, SnS2-QDs are predicted as one of the promising inorganic quantum dots. However, investigation on the photoluminescence property of SnS2 QDs and its biosensing applications is limited. Therefore, it needs serious exploration. In this work, we report the synthesis of in-situ functionalized fluorescent tin disulfide quantum dots (f-SnS2 QDs) using one-step bottom-up hydrothermal technique. The obtained f-SnS2 QDs are monodispersed in nature and exhibits strong blue fluorescence under UV exposure with a high quantum yield (QY ~8.7%) in aqueous medium. Interestingly, it is observed that fluorescence of f-SnS2 QDs significantly quenched in the presence of Fe3+ ions. The developed optical sensor shows linear response for Fe3+ ions in the concentration range of 0 μM–68 μM (~0.84 μM detection limit). Further, to understand the quenching kinetics, the PL and TRPL studies are conducted which reveal that the quenching phenomenon is both static as well as dynamic in nature. The underneath detailed mechanism is also discussed in the paper.

Thiol-Anchored TIPS-Tetracene Ligands with Quantitative Triplet Energy Transfer to PbS Quantum Dots and Improved Thermal Stability.

Triplet energy transfer between inorganic quantum dots (QDs) and organic materials plays a fundamental role in many optoelectronic applications based on these nanocomposites. Attaching organic molecules to the QD as transmitter ligands has been shown to facilitate transfer both to and from QDs. Here we show that the often disregarded thiol anchoring group can achieve quantitative triplet energy transfer yields in a PbS QD system with 6,11-bis[(triisopropylsilyl)ethynyl]tetracene-2-methylthiol (TET-SH) ligands. We demonstrate efficient triplet transfer in a singlet fission-based photon multiplication system with 5,12-bis[(triisopropylsilyl)ethynyl]tetracene generating triplets in solution that transfer to the PbS QDs via the thiol ligand TET-SH. Importantly, we demonstrate the increased thermal stability of the PbS/TET-SH system, compared to the traditional carboxylic acid counterpart, allowing for higher photoluminescence quantum yields.

Enhancing the efficiency of green perovskite-QDs-based light-emitting devices by controlling interfacial defects with diamine molecules

Inorganic perovskite quantum dots (QDs) have emerged as promising materials for light-emitting devices by merits of their high photoluminescence quantum yield (PLQY), narrow full width at half-maximum and tunable emission spectrum. However, fluorescence quenching and trap-mediated nonradiative recombination between hole transport layer (HTL) and QD films are prejudicial to the performance of perovskite-QDs-based light-emitting devices (QLEDs). Here, HTL was modified with diamine molecules (1,4-butanediamine (4-DA), 1,8-octyldiamine (8-DA) and 1,11-aminoundecylamine (11-DA)) through a simple self-assembly method. QD films based on modified poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (Poly-TPD) exhibited higher PL intensity and lower fluorescence quenching properties. Meanwhile, diamine molecules do favor to the flatness of Poly-TPD film and contribute to the smoothness of QD films. Moreover, the exciton quenching and the density of defects at the interface between HTL and QD films were effectively reduced. Particularly, QLEDs based on HTL modified with 8-DA was endowed with a maximum luminance of 78634 cd/m2, a peak current efficiency of 30.77 cd/A, a maximum external quantum efficiency of 8.90% and T50 of 16.8 min when the initial brightness is about 1000 cd/m2.

Improved stability and performance of all inorganic perovskite quantum dots synthesized directly with N-alkylmonoamine ligands for light-erasable transistor memory

All inorganic perovskite quantum dots (PeQDs) of CsPbX3 (X = Cl, Br, I, or their mixture) are regarded as promising candidates for photovoltaics and optoelectronic devices owing to their excellent and unique optical and electronic properties. However, their inherent poor stability severely limits their practical applications. Herein, aiming at improving their stability and photoluminescence (PL) properties, a novel surface capping ligand strategy was performed via directly synthesizing CsPbX3 quantum dots (QDs) by hot injection method with straight-chain n-alkylmonoamine instead of conventional organic amine (oleylamine) as ligands. With stronger intermolecular interaction and denser alignment, n-alkylmonoamine ligands would form a stable protective layer on the surface of PeQDs. As a result, the n-alkylmonoamine capped CsPbBr3 QDs exhibited remarkable long-term storage with 70% of PLQY retaining after 30 days in the open air, impressive water resistance for over 1 h in water, significant photostability with hour-scale laser exposure, and high thermal stability with 60% of PLQY retaining after heating at 80 °C for over 60 min. In addition, by blending the CsPbBr3 QDs with polymer as the gate dielectric, novel light-erasable transistor memories were fabricated based on the device architecture of a floating-gate transistor memory (FGOTM). Acting as dense charge tunneling layers for charge trapping materials (PeQDs) in light-erasable transistor memory, the alkylmonoamine ligand layers led to significant broadening of memory windows, presenting various charge capture abilities of the PeQDs with the different capping ligands.

Number of Surface-Attached Acceptors on a Quantum Dot Impacts Energy Transfer and Photon Upconversion Efficiencies

Composites of organic molecules and inorganic quantum dots (QDs) have emerged as attractive photon upconversion systems that use triplet–triplet annihilation upconversion (TTA-UC). However, the upc...