Enhanced light emission of quantum dot films by scattering of poly(zinc methacrylate) coating CdZnSeS/ZnS quantum dots and high refractive index BaTiO3 nanoparticles

Quantum dots (QDs) have received considerable attention in information displays owing to their high quantum yield, high colour purity and low-cost fabrication. However, light emission for ultra-thin QD films with low mass percentage of QDs still need to be improved because the blue light can directly transmit the films, leading to insufficient energy to excite the QDs. In this study, we report QD films based on a poly(zinc methacrylate) coating with alloyed green-emitting CdZnSeS/ZnS quantum dots (QDs@PZnMA) together with high refractive-index BaTiO₃ nanoparticles to enhance the scattering coefficient of the QD films. Results demonstrate a 7.5-fold increase in the absorption coefficient, 11.3-fold increase in the scattering coefficient, 8.5-fold increase in the optical density (OD) and 8.6-fold increase in the green-light emission of QD films, compared with films that have the same mass percentage of pristine QDs. This approach provides a promising strategy for developing QD optical films with high scattering and enhanced light emission for flexible displays.

We report QD films based on a poly(zinc methacrylate) coating with alloyed green-emitting CdZnSeS/ZnS quantum dots (QDs@PZnMA) together with high refractive-index BaTiO₃ nanoparticles to enhance the scattering coefficient of the QD films.     

Metal-enhanced fluorescence in polymer composite films with Au@Ag@SiO2 nanoparticles and InP@ZnS quantum dots

For white light-emitting diode (LED) applications, semiconductor quantum dots (QDs) have been widely utilized as efficient down-converters to change the blue color of the light source into different emission colors. Because QDs offer spectral tunability over the entire visible light range, as well as improved color purity, they have rapidly replaced conventional phosphor-based white LEDs. However, for the sustainable growth of QD-mediated LEDs, the amount of QDs required must be reduced by enhancing the color-conversion efficiency. For this purpose, we prepared poly(lauryl methacrylate) (PLMA) composite films by the photo-crosslinking polymerization of lauryl methacrylate monomers in the presence of Au@Ag@SiO₂ nanoparticles (NPs) and InP@ZnS QDs. In the PLMA composites, the Au@Ag NPs not only amplified the blue light source but also modified the relaxation of the excited QDs via localized surface plasmon resonance. This resulted in a maximum 12.9-fold enhancement in the QD fluorescence. Because the blue light source in this study can be easily replaced by blue LEDs, the enhanced efficiency of QD emissions via the plasmonic effect could potentially increase the performance of QDs for display applications.

Poly(lauryl methacrylate) films containing Au@Ag@SiO₂ nanoparticles and InP@ZnS quantum dots were prepared to investigate metal-enhanced fluorescence in polymer composites.     

Cholesteric mesophase based 1D photonic materials from self-assembly of liquid crystalline block and random terpolymers containing chromonic molecules

We describe the influence of competing self-organizing phenomena on the formation of cholesteric mesophase in liquid crystalline brush block terpolymers (LCBBTs) and liquid crystalline random brush terpolymers (LCRBTs) containing chromonic molecules. A library of LCBBTs and LCRBTs are synthesized using ring-opening metathesis polymerization (ROMP) of norbornene side-chain functionalized monomers comprising cholesteryl mesogen (NBCh₉), chromonic xanthenone (NBXan), and poly(ethylene glycol) (NBMPEG). Compression molded films of LCRBTs containing chromonic molecules display multilevel hierarchical structure in which cholesteric mesophase co-exists with π–π stacking of the chromonic mesophase along with PEG microphase segregated domains. This is unexpected as conventional LCBCPs and LCBBCs that lack chromonic molecules do not form cholesteric mesophases. The presence of π–π interactions modifies the interface at the IMDS so that both chromonic and cholesteric mesophases coexist leading to the manifestation of cholesteric phase for the first time within block architecture and is very reminiscent of previously published LCRBCs without chromonic molecules. The key to the observed hierarchical assembly in these LCBBTs containing chromonic molecules lies in the interplay of LC order, chromonic π–π stacking, PEG side chain microphase segregation, and their supramolecular cooperative motion. This unique “single component” polymer scaffold transforms our capacity to attain nanoscale hierarchies and optical properties from block architecture similar to nanoscale mesophases resulting in random architecture.

We describe the influence of competing self-organizing phenomena on the formation of cholesteric mesophase in liquid crystalline brush block terpolymers (LCBBTs) and liquid crystalline random brush terpolymers (LCRBTs) containing chromonic molecules.     

Static and dynamic electro-optical properties of liquid crystals mediated by ferroelectric polymer films

This paper reports the electro-optical properties of high resistivity nematic liquid crystals sandwiched between ferroelectric polymer films. Interactions between liquid crystals and the film result in a series of interesting optical and electro-optical features. For example, the visualization of ferroelectric domains by means of liquid crystals has been known for decades. However, here we demonstrate that liquid crystals can also reveal the fractal dimension of multi—domain poly(vinylidene fluoride)-based films. Unidirectionally rubbed films made of poly(vinylidene fluoride)-based (PVDF) materials align liquid crystals (LC) homogeneously, with the pretilt angle on the order of 1–2 degrees. This property was implemented in the design of hybrid cells composed of liquid crystals sandwiched between PVDF-based films. The designed PVDF|LC|PVDF cells exhibit tunable electro-optical performance originating from the presence of the PVDF-based films. More specifically, (i) the threshold voltage characterizing the transition of liquid crystals from a planar to a homeotropic state can be tuned by varying the film thickness, and (ii) total fall time (turn-off time) can be controlled by varying the frequency and amplitude of the driving voltage. This frequency dependence of the fall time is strongly pronounced at a relatively high voltage applied across the cell. In the low frequency regime, an increase in the turn-off time can be approximated as a linear function of the applied electric field. An electric-field induced polarization of the PVDF-based films is considered a major reason leading to the afore-mentioned amplitude and frequency dependence of the switching time.

Liquid crystals (LC) can reveal the fractal dimension of multi-domain ferroelectric films (FF) while these films can control the switching time of FF–LC hybrids.     

Biocompatible quantum dot-antibody conjugate for cell imaging,targeting and fluorometric immunoassay: crosslinking,characterization and applications

Quantum dots (QDs) are important fluorescent probes that offer great promise for bio-imaging research due to their superior optical properties. However, QDs for live cell imaging and the tracking of cells need more investigation to simplify processing procedures, improving labeling efficiency, and reducing chronic toxicity. In this study, QDs were functionalized with bovine serum albumin (BSA) via a chemical linker. Anti-human immunoglobulin antibodies were oxidized by sodium periodate to create reactive aldehyde groups for a spontaneous reaction with the amine groups of BSA-modified QDs. An antibody-labeled QD bioconjugate was characterized using agarose gel electrophoresis, dynamic light scattering, and zeta potential. Using fluorescence spectroscopy, we found that the fluorescence of QDs was retained after multiple conjugation steps. The cell-labeling function of the QD bioconjugate was confirmed using an image analyzer and confocal microscopy. The QD bioconjugate specifically targeted human immunoglobulin on the membrane surface of recombinant cells. In addition, the QD bioconjugate applied in fluorometric immunoassay was effective for the quantitative analysis of human immunoglobulin in an enzyme-linked immunosorbent assay. The developed QD bioconjugate may offer a promising platform to develop biocompatible tools to label cells and quantify antibodies in the immunoassay.

A layer-by-layer covalent strategy is developed including the modification of QDs using BSA as a stabilizing agent and then anti-human immunoglobulin antibody as a targeting moiety.     

Unprecedented surface stabilized InP quantum dots with bidentate ligands

For InP-based QDs, the current technology does not outperform CdSe-based QDs in many respects, one of which is stability. The optical stability of QDs is closely related to their surface properties, so QDs often use organic ligands for surface protection. These organic ligands are dynamically attached and detached on the QD surface; during detachment, their surfaces are easily damaged and oxidized, thereby deteriorating their optical characteristics. Therefore, we have synthesized a ligand 1,2-hexadecanedithiol with a bidentate form, inducing one ligand to bind to the QD surface strongly through the chelate effect, as a good way to improve the stability of the QDs; thus, the PL stability of the green-light-emitting InP-based QDs was greatly increased. To confirm the existence of the dithiol ligand, we used thermogravimetric analysis/simultaneous thermal analysis-mass spectroscopy (TGA/STA-MS). After that, we applied the ligand to blue-light-emitting ZnSe QDs and red-light-emitting InP QDs, and for those two types of QD we also confirmed that the stability was increased. Additionally, we tested dithiol exchanged QDs at a high temperature of 150 °C, and the increase of stability was effective even in a high temperature condition.

For InP-based QDs, the current technology does not outperform CdSe-based QDs in many respects, one of which is stability.     

Poly(ethylene glycol) brush-b-poly(N-vinylpyrrolidone)-based double hydrophilic block copolymer particles crosslinked via crystalline α-cyclodextrin domains

Self-assembly of block copolymers is a significant area of polymer science. The self-assembly of completely water-soluble block copolymers is of particular interest, albeit a challenging task. In the present work the self-assembly of a linear-brush architecture block copolymer, namely poly(N-vinylpyrrolidone)-b-poly(oligoethylene glycol methacrylate) (PVP-b-POEGMA), in water is studied. Moreover, the assembled structures are crosslinked via α-CD host/guest complexation in a supramolecular way. The crosslinking shifts the equilibrium toward aggregate formation without switching off the dynamic equilibrium of double hydrophilic block copolymer (DHBC). As a consequence, the self-assembly efficiency is improved without extinguishing the unique DHBC self-assembly behavior. In addition, decrosslinking could be induced without a change in concentration by adding a competing complexation agent for α-CD. The self-assembly behavior was followed by DLS measurement, while the presence of the particles could be observed via cryo-TEM before and after crosslinking.

Self-assembly of the double hydrophilic block copolymer poly(N-vinylpyrrolidone)-b-poly(oligoethylene glycol methacrylate) and supramolecular crosslinking via α-cyclodextrin in water is presented.     

Screening and characterisation of CdTe/CdS quantum dot-binding peptides for material surface functionalisation

Quantum dots (QDs) are promising nanomaterials due to their unique photophysical properties. For them to be useful in biological applications, the particle surface generally needs to be conjugated to biological molecules, such as antibodies. In this study, we screened CdTe/CdS QD-binding peptides from a phage display library as linkers for simple and bio-friendly QD modification. Among five QD-binding peptide candidates, a series of truncated peptides designed from two high-affinity peptides were subjected to an array-based binding assay with QDs to assess their functional core sequences and characteristics. Linking these isolated, shortened peptides (PWSLNR and SGVYK) with an antibody-binding peptide (NKFRGKYK) created dual-functional peptides that are capable of QD surface functionalisation by antibodies. Consequently, the dual-functional peptides could mediate anti-CD9 antibody functionalisation onto CdTe/CdS QD surface; CD9 protein imaging of cancer cells was also demonstrated. Our proposed peptides offer an effective vehicle for QD surface functionalisation in biological applications.

We explored peptide binders to quantum dots (QDs) and proposed a simple and bio-friendly QD functionalisation using dual-functional peptides.     

Photoluminescence color stability of green-emitting InP/ZnS core/shell quantum dots embedded in silica prepared via hydrophobic routes

In this work, green-emitting InP/ZnS quantum dots (QDs) modified with 1-dodecanethiol were embedded into silica by two methods to improve their photostability while maintaining a high photoluminescence quantum yield (PLQY) and a color coordinate. A monolithic QD-silica composite prepared by a non-aqueous route with tetraethyl orthosilicate and lactic acid featured low transparency, a loss of the color purity of green, and a PLQY of 1.6%, which was considerably lower than that of the original QDs (67%). The decrease of the PLQY was attributed to QD aggregation in the sol–gel process and degradation of the QDs by the acid. The alternative method involved stirring a toluene dispersion of the QDs with tetramethyl orthosilicate (TMOS) for 20 h or 7 days. The PLQY of the TMOS-modified InP/ZnS QDs (20 h) was 62%, which was only slightly lower than that of the original QDs. The PLQY decreased to 52% when the duration of aging was prolonged to 7 days. This decrease was attributed to desorption of surface modifiers from the QD surface and oxidative degradation by oxygen dissolved in toluene. Herein, the color coordinate was maintained stably. Photostability was evaluated by continuous irradiation of the samples by a blue light emitting diode. The decrease of photoluminescence (PL) intensity was suppressed by the silica encapsulation. In particular, the PL intensity of the TMOS-modified InP/ZnS QD sample (7 d) maintained 99% of its initial intensity. Silica encapsulation of InP/ZnS QDs prevented contact of the QDs with oxygen in the air, resulting in improved photostability.

We prepared and characterized green-emitting silica composites containing InP/ZnS QDs with excellent quantum yield, emission color purity, and photostability.     

Hydrothermal synthesis of water-soluble Mn- and Cu-doped CdSe quantum dots with multi-shell structures and their photoluminescence properties

Optical properties of semiconductor quantum dots (QDs) can be tuned by doping with transition metal ions. In this study, water-soluble CdSe/ZnS:Mn/ZnS QDs with the core/shell/shell structure were synthesized through a hydrothermal method, in which the surface of the CdSe core was coated with a ZnS:Mn shell and ZnS capping shell. Herein, the CdSe core QDs were prepared first and then doped with Mn²⁺; therefore, the QD size and doping level could be controlled independently and interference from the self-purifying effect could be avoided. When CdSe cores with diameters less than 1.9 nm were used, Mn-related photoluminescence (PL) was observed as the main PL band, whereas the band-edge PL was mainly observed when larger CdSe cores were used. Furthermore, using ZnS:Cu as the doping shell layer, CdSe/ZnS:Cu/ZnS and ZnSe/ZnS:Cu/ZnS nanoparticles were successfully synthesized, and Cu-related PL was clearly observed. These results indicate that the core/shell/shell QD structure with doping in the shell layer is a versatile method for synthesizing doped QDs.

The core/shell/shell QD structure with doping in the shell layer is a versatile method for synthesizing doped QDs.     

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.     

Highly transparent phototransistor based on quantum-dots and ZnO bilayers for optical logic gate operation in visible-light

Highly transparent optical logic circuits operated with visible light signals are fabricated using phototransistors with a heterostructure comprised of an oxide semiconductor (ZnO) with a wide bandgap and quantum dots (CdSe/ZnS QDs) with a small bandgap. ZnO serves as a highly transparent active channel, while the QDs absorb visible light and generate photoexcited charge carriers. The induced charge carriers can then be injected into the ZnO conduction band from the QD conduction band, which enables current to flow to activate the phototransistor. The photoexcited charge transfer mechanism is investigated using time-resolved photoluminescence spectroscopy, scanning Kelvin probe microscopy, and ultraviolet photoelectron spectroscopy. Measurements show that carriers in the QD conduction band can transfer to the ZnO conduction band under visible light illumination due to a change in the Fermi energy level. Moreover, the barrier for electron injection into the ZnO conduction band from the QD conduction band is low enough to allow photocurrent generation in the QDs/ZnO phototransistor. Highly transparent NOT, NOR, and NAND optical logic circuits are fabricated using the QDs/ZnO heterostructure and transparent indium tin oxide electrodes. This work provides a means of developing highly transparent optical logic circuits that can operate under illumination with low-energy photons such as those found in visible light.

The operation of highly transparent optical logic circuits composed of phototransistors with QDs/ZnO heterojunctions are demonstrated. Photoexcited charge transfer mechanism was confirmed for photoinduced carriers transfer at the QDs/ZnO interfaces.     

Ice-regenerated flame retardant and robust film of Bombyx mori silk fibroin and POSS nano-cages

In this study, we present a simple method to prepare and control the structure of regenerated hybrid silkworm silk films through icing. A regenerated hybrid silk (RHS) film consisting of a micro-fibrillar structure was obtained by partially dissolving amino-functionalized polyhedral oligomeric silsesquioxanes (POSS) and silk fibers in a CaCl₂–formic acid solution. After immersion in water and icing, the obtained films of RHS showed polymorphic and strain-stiffening behaviors with mechanical properties that were better than those observed in dry or wet-regenerated silk. It was also found that POSS endowed the burning regenerated silk film with anti-dripping properties. The higher β-sheet content observed in the ice-regenerated hybrid micro-fibrils indicates a useful route to fabricate regenerated silk with physical and functional properties, i.e. strain-stiffening, similar to those observed to date in natural spider silk counterpart and synthetic rubbers, and anti-dripping of the flaming melt. Related carbon nanotube composites are considered for comparison.

In this study, we present a simple method to prepare and control the structure of regenerated hybrid silkworm silk films through icing.     

Flexible translucent chitosan–glycerin/QD nanocomposite glue for anti-counterfeiting films with strong adhesion and stability

With the rapid development of commodity circulation, more attention has been paid to the anticounterfeiting technology of commodities, including stability, universality and ease of distinguishing. The authors report the use of gelatin–chitosan–glycerin/QD nanocomposite-functionalized glue for luminescent anti-counterfeiting labels. As the blend and plasticizer, the addition of chitosan and glycerin effectively improved the flexibility and formability of the gelatin–chitosan–glycerin/QD composite films, which show excellent mechanical properties, including high transparency, luminescence and flexibility, and they are easy to prepare on a large scale, providing certain reference values for new anticounterfeiting technology applying a variety of morphologies.

Flexible translucent anticounterfeiting QD films with strong adhesion and stability.     

Vertical liquid crystal orientation of phytochemical-based oryzanol modified polystyrene

Using plant-derived oryzanol, we synthesized a series of phytochemical-based oryzanol-modified polystyrenes (PORZ#, # = 20, 40, 60, 80, or 100, where # is the mole fraction of the oryzanol moiety) using polymer modification reactions in order to investigate their liquid crystal (LC) orientation behaviors. Generally, an LC cell made from polymer films with a higher mole fraction of the oryzanol side group showed vertical LC orientation behavior. The vertical orientation behavior was strongly correlated with the surface energy of these polymer films. For instance, the vertical orientation was observed when the polymer''s surface energy, which is influenced by the nonpolar and long carbon groups, was less than about 40.42 mJ m⁻². Good electro-optical properties, such as the aligning stabilities at 250 °C and ultraviolet (UV) irradiation of 20 J cm⁻², the voltage holding ratio, and the residual DC voltage (R-DC), were observed for the LC cells fabricated using PORZ100 as an eco-friendly LC orientation layer.

The liquid crystal (LC) orientation properties on phytochemical oryzanol modified polystyrene film were investigated. This can contribute to development of eco-friendly LC orientation layers based on bioavailable resources containing polymer films.     

Polymer encapsulation of anticancer silver–N-heterocyclic carbene complexes

Amphiphilic block copolymers have been developed for the encapsulation of organometallic drugs. silver–N-heterocyclic carbene complexes have shown significant promise as anticancer and antibacterial compounds, and have been studied as the payload in these carriers. Simple modification of the N-heterocyclic carbene ligand structure enables solubility properties and interaction with the polymer to be tuned.

Amphiphilic block copolymers have been developed for the encapsulation of silver anticancer drugs.     

Novel post-synthesis purification strategies and the ligand exchange processes in simplifying the fabrication of PbS quantum dot solar cells

Quantum dots (QDs) solids with iodide passivation are a key component for most of the well-performing PbS QDs solar cells. Usually, iodide passivation of oleic acid (OA) capped PbS QDs films is achieved by a solid-state ligand exchange process using tetrabutylammonium iodide (TBAI). This ligand exchange process has generally been reported to be incomplete, especially in higher thicknesses, affecting the properties of the films adversely, producing inconsistent results in the device structures fabricated. The present study is based on a systematic investigation of the TBAI exchange on PbS QDs films and the performance of the resulting solar cells. We could achieve a complete TBAI exchange in a sufficiently thick (∼240 nm) and dense QDs film deposited by a minimum number of coating steps, through the optimization of the number of post-synthesis washing cycles on the QDs. Detailed studies were carried out investigating the effect of the number of washing cycles on the quantity of OA before and after the exchange, the ligand exchange efficiency, the development of trap states and the resulting photovoltaic device performance. A power conversion efficiency of 5.55% was obtained for a device subjected to an optimum number of washing cycles.

Quantum dots (QDs) solids with iodide passivation are a key component for most of the well-performing PbS QDs solar cells.     

Enhanced,parallel liquid crystal alignment based on polystyrene substituted with phthalimidoyl groups

A series of polystyrene (PS) polymers substituted with phthalimide (PPH#), where # is the degree of substitution, were synthesized via a polymer analogous reaction to investigate liquid crystal (LC) alignment behaviors of LC cells fabricated using PPH# films. The PPH# films exhibited higher optical transparency in the visible light region compared to a commercial polyimide (PI) film. The transmittance of each PPH# film ranged from 91 to 93%, whereas that of PI was 80.5% at 550 nm. The LC cell fabricated with a pristine PS film showed planar LC alignment perpendicular with respect to the rubbing direction. The introduction of the phthalimide group to the side chain of PS diverted the LC alignment direction from perpendicular to parallel with respect to the rubbing direction. The LC cells fabricated with PPH# films exhibited planar LC alignment parallel with respect to the rubbing direction when the degree of substitution of phthalimidoyl moieties was >20 mol%. In addition, the long-term stability of the LC cell composed of pristine PS was very low. However, the long-term stability of the LC cells fabricated with the PPH# series was remarkably enhanced in addition to their ultraviolet stability. Therefore, this study contributes to the development of planar and parallel LC alignments on PS derivatives and can be used in the next-generation display industry for the production of flexible displays.

Polystyrene substituted with phthalimide can enhance liquid crystal alignment behavior and stability and switch orientation direction from perpendicular to parallel.     

Full-color-emitting (CuInS2)ZnS-alloyed core/shell quantum dots with trimethoxysilyl end-capped ligands soluble in an ionic liquid

Zinc-copper-indium sulfide (ZCIS)-alloyed quantum dots are emerging as a new family of low toxic I–III–VI semiconductors due to their broad and color-tunable emissions as well as large Stokes shifts. Here, we fabricated a series of ZCIS QDs with tunable PL wavelengths and band-gap energies via a facile strategy by varying the ratio of A1–3 stock (Cu⁺/In³⁺) to the B stock (Zn²⁺) content. The ZnS shell was formed to improve the PL emission efficiency of the core nanoparticles and the PL emission wavelength of the resulting ZCIS/ZnS NCs gradually blue-shifted with an increase in the number of shell layers, resulting in a wide range of emissions from 800 nm to 518 nm that can be tuned by the core compositions or shell layer numbers for ZCIS/ZnS. Finally, the long-chain ligands dodecanethiol/octadecylamine on the quantum dots'' surface were efficiently replaced by (3-mercaptopropyl)trimethoxysilane, thus enabling their solubility in an ionic liquid, which was confirmed via GC-MS. It also benefited for the co-dissolution of the polymers and chemical binding with other materials through the reactive silanol group, which provide stable and well-distributed ZCIS/ZnS QDs composites or surface coating by the QDs.

ZCIS QDs were fabricated by varying ratio stock A to stock B. PL intensity enhanced and blue shift as shell layers increase. Emissions covering 800 nm to 518 nm tuned by compositions or shell layers. Ligand exchanged by MPtMS enable solubility in IL.     

A near-infrared photoinverter based on ZnO and quantum-dots

Near-infrared (NIR) photoswitching transistors have been fabricated using a hybrid structure of zinc oxide (ZnO) and quantum-dots (QDs). The ZnO active layer was prepared using a solution process, while colloidal QDs were inserted between a silicon dioxide (SiO₂) gate insulator and a ZnO active layer. The small band gap QDs (1.59 eV) were used to absorb low-energy NIR photons, generate photo-excited carriers, and inject them into the conduction band of the ZnO film. The device with the interfacial QDs induced photocurrents upon exposure to 780 nm-wavelength light. The photoresponsivity of the ZnO/QD device was 0.06 mA W⁻¹, while that of the device without QDs was 1.7 × 10⁻⁵ mA W⁻¹, which indicated that the small band gap QDs enabled a photo-induced current when exposed to NIR light. Furthermore, a photoinverter was prepared which was composed of a ZnO/QDs phototransistor and a load resistor. Photoswitching characteristics indicated that the photoinverter was well modulated by a periodic light signal of 780 nm in wavelength. The results demonstrate a useful way to fabricate NIR optoelectronics based on ZnO and QDs.

A near-infrared photoinverter was fabricated based on ZnO and quantum-dots. We found that the small band gap quantum-dots could absorb low-energy near-infrared photons, generate photo-excited carriers, and inject them into the conduction band of ZnO.