Ultrathin,Core–Shell Structured SiO2 Coated Mn2+‐Doped Perovskite Quantum Dots for Bright White Light‐Emitting Diodes

All‐inorganic semiconductor perovskite quantum dots (QDs) with outstanding optoelectronic properties have already been extensively investigated and implemented in various applications. However, great challenges exist for the fabrication of nanodevices including toxicity, fast anion‐exchange reactions, and unsatisfactory stability. Here, the ultrathin, core–shell structured SiO₂ coated Mn²⁺ doped CsPbX₃ (X = Br, Cl) QDs are prepared via one facile reverse microemulsion method at room temperature. By incorporation of a multibranched capping ligand of trioctylphosphine oxide, it is found that the breakage of the CsPbMnX₃ core QDs contributed from the hydrolysis of silane could be effectively blocked. The thickness of silica shell can be well‐controlled within 2 nm, which gives the CsPbMnX₃@SiO₂ QDs a high quantum yield of 50.5% and improves thermostability and water resistance. Moreover, the mixture of CsPbBr₃ QDs with green emission and CsPbMnX₃@SiO₂ QDs with yellow emission presents no ion exchange effect and provides white light emission. As a result, a white light‐emitting diode (LED) is successfully prepared by the combination of a blue on‐chip LED device and the above perovskite mixture. The as‐prepared white LED displays a high luminous efficiency of 68.4 lm W^?1 and a high color‐rendering index of Ra = 91, demonstrating their broad future applications in solid‐state lighting fields.     

Light‐Emitting Diodes with Cu‐Doped Colloidal Quantum Wells: From Ultrapure Green,Tunable Dual‐Emission to White Light

Copper‐doped colloidal quantum wells (Cu‐CQWs) are considered a new class of optoelectronic materials. To date, the electroluminescence (EL) property of Cu‐CQWs has not been revealed. Additionally, it is desirable to achieve ultrapure green, tunable dual‐emission and white light to satisfy the various requirement of display and lighting applications. Herein, light‐emitting diodes (LEDs) based on colloidal Cu‐CQWs are demonstrated. For the 0% Cu‐doped concentration, the LED exhibits Commission Internationale de L'Eclairage 1931 coordinates of (0.103, 0.797) with a narrow EL full‐wavelength at half‐maximum of 12 nm. For the 0.5% Cu‐doped concentration, a dual‐emission LED is realized. Remarkably, the dual emission can be tuned by manipulating the device engineering. Furthermore, at a high doping concentration of 2.4%, a white LED based on CQWs is developed. With the management of doping concentrations, the color tuning (green, dual‐emission to white) is shown. The findings not only show that LEDs with CQWs can exhibit polychromatic emission but also unlock a new direction to develop LEDs by exploiting 2D impurity‐doped CQWs that can be further extended to the application of other impurities (e.g., Mn, Ag).     

Polarized Light‐Emitting Diodes Based on Patterned MoS2 Nanosheet Hole Transport Layer

Here, this study successfully fabricates few‐layer MoS₂ nanosheets from (NH₄)₂MoS₄ and applies them as the hole transport layer as well as the template for highly polarized organic light‐emitting diodes (OLEDs). The obtained material consists of polycrystalline MoS₂ nanosheets with thicknesses of 2 nm. The MoS₂ nanosheets are patterned by rubbing/ion‐beam treatment. The Raman spectra shows that {poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole), poly[(9,9‐di‐n‐octylfluorenyl‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,8‐diyl)]} (F8BT) on patterned MoS₂ exhibits distinctive polarization behavior. It is discovered that patterned MoS₂ not only improves the device efficiency but also changes the polarization behavior of the devices owing to the alignment of F8BT. This work demonstrates a highly efficient polarized OLED with a polarization ratio of 62.5:1 in the emission spectrum (166.7:1 at the peak intensity of 540 nm), which meets the manufacturing requirement. In addition, the use of patterned MoS₂ nanosheets not only tunes the polarization of the OLEDs but also dramatically improves the device performance as compared with that of devices using untreated MoS₂.     

Eu3+, Sm3+ Deep‐Red Phosphors as Novel Materials for White Light‐Emitting Diodes and Simultaneous Performance Enhancement of Organic–Inorganic Perovskite Solar Cells

The luminous efficiency of inorganic white light‐emitting diodes, to be used by the next generation as light initiators, is continuously progressing and is an emerging interest for researchers. However, low color‐rendering index (Ra), high correlated color temperature (CCT), and poor stability limit its wider application. Herein, it is reported that Sm³⁺‐ and Eu³⁺‐doped calcium scandate (CaSc₂O₄ (CSO)) are an emerging deep‐red‐emitting material with promising light absorption, enhanced emission properties, and excellent thermal stability that make it a promising candidate with potential applications in emission display, solid‐state white lighting, and the device performance of perovskite solar cells (PSCs). The average crystal structures of Sm³⁺‐doped CSO are studied by synchrotron X‐ray data that correspond to an extremely rigid host structure. Samarium ion is incorporated as a sensitizer that enhances the emission intensity up to 30%, with a high color purity of 88.9% with a 6% increment. The impacts of hosting the sensitizer are studied by quantifying the lifetime curves. The CaSc₂O₄:0.15Eu³⁺,0.03Sm³⁺ phosphor offers significant resistance to thermal quenching. The incorporation of lanthanide ion‐doped phosphors CSOE into PSCs is investigated along with their potential applications. The CSOE‐coated PSCs devices exhibit a high current density and a high power conversion efficiency (15.96%) when compared to the uncoated control devices.     

Room‐Temperature Triple‐Ligand Surface Engineering Synergistically Boosts Ink Stability,Recombination Dynamics,and Charge Injection toward EQE‐11.6% Perovskite QLEDs

Developing low‐cost and high‐quality quantum dots (QDs) or nanocrystals (NCs) and their corresponding efficient light‐emitting diodes (LEDs) is crucial for the next‐generation ultra‐high‐definition flexible displays. Here, there is a report on a room‐temperature triple‐ligand surface engineering strategy to play the synergistic role of short ligands of tetraoctylammonium bromide (TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid (OTAc) toward “ideal” perovskite QDs with a high photoluminescence quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel, stable ink characteristics, and effective charge injection and transportation in QD films, resulting in the highly efficient QD‐based LEDs (QLEDs). Furthermore, the QD films with less nonradiative recombination centers exhibit improved PL properties with a PLQY of 61% through dopant engineering in A‐site. The robustness of such properties is demonstrated by the fabrication of green electroluminescent LEDs based on CsPbBr₃ QDs with the peak external quantum efficiency (EQE) of 11.6%, and the corresponding peak internal quantum efficiency (IQE) and power efficiency are 52.2% and 44.65 lm W^?1, respectively, which are the most‐efficient perovskite QLEDs with colloidal CsPbBr₃ QDs as emitters up to now. These results demonstrate that the as‐obtained QD inks have a wide range application in future high‐definition QD displays and high‐quality lightings.     

Optical properties of Eu<Superscript>3+</Superscript> activated SrLa<Subscript>2</Subscript>O<Subscript>4</Subscript> red-emitting phosphors for WLED applications

The SrLa_2?xO₄:xEu³⁺ phosphors are synthesized through high-temperature solid-state reaction method at 1473 K with various doping concentration. Their phase structures, absorption spectra, and luminescence properties are investigated by X-ray diffraction (XRD), UV–Vis spectrophotometer and photoluminescence spectrometry. The intense absorption of SrLa_2?xO₄:xEu³⁺ phosphors have occurred around 400 nm. The prominent luminescence spectra of the prepared phosphors exhibited bright red emission at 626 nm. The doping concentration 0.12 mol% of Eu³⁺ is shown to be optimal for prominent red emission and chromaticity coordinates are x?=?0.692, y?=?0.3072. Considering the high colour purity and appropriate emission intensity of Eu³⁺ doped SrLa₂O₄ can be used as red phosphors for white light emitting diodes (WLEDs).     

How Effective is Plasmonic Enhancement of Colloidal Quantum Dots for Color‐Conversion Light‐Emitting Devices?

Enhancing the fluorescence intensity of colloidal quantum dots (QDs) in case of color‐conversion type QD light‐emitting devices (LEDs) is very significant due to the large loss of QDs and their quantum yields during fabrication processes, such as patterning and spin‐coating, and can therefore improve cost‐effectiveness. Understanding the enhancement process is crucial for the design of metallic nanostructure substrates for enhancing the fluorescence of colloidal QDs. In this work, improved color conversion of colloidal green and red QDs coupled with aluminum (Al) and silver (Ag) nanodisk (ND) arrays designed by in‐depth systematic finite‐difference time domain simulations of excitation, spontaneous emission, and quantum efficiency enhancement is reported. Calculated results of the overall photoluminescence enhancement factor in the substrate of 500 × 500 µm² size are 2.37‐fold and 2.82‐fold for Al ND‐green QD and Ag ND‐red QD structures, respectively. Experimental results are in good agreement, showing 2.26‐fold and 2.66‐fold enhancements for Al ND and Ag ND structures. Possible uses of plasmonics in cases such as white LED and total color conversion for possible display applications are discussed. The theoretical treatments and experiments shown in this work are a proof of principle for future studies of plasmonic enhancement of various light‐emitting materials.     

Designable Luminescence with Quantum Dot–Silver Plasmon Coupler

We explore a strongly interacting QDs/Ag plasmonic coupling structure that enables multiple approaches to manipulate light emission from QDs. Group II–VI semiconductor QDs with unique surface states (SSs) impressively modify the plasmonic character of the contiguous Ag nanostructures whereby the localized plasmons (LPs) in the Ag nanostructures can effectively extract the non‐radiative SSs of the QDs to radiatively emit via SS–LP resonance. The SS–LP coupling is demonstrated to be readily tunable through surface‐state engineering both during QD synthesis and in the post‐synthesis stage. The combination of surface‐state engineering and band‐tailoring engineering allows us to precisely control the luminescence color of the QDs and enables the realization of white‐light emission with single‐size QDs. Being a versatile metal, the Ag in our optical device functions in multiple ways: as a support for the LPs, for optical reflection, and for electrical conduction. Two application examples of the QDs/Ag plasmon coupler for optical devices are given, an Ag microcavity + plasmon‐coupling structure and a new QD light‐emitting diode. The new QDs/Ag plasmon coupler opens exciting possibilities in developing novel light sources and biomarker detectors.     

Inorganic Nano Light‐Emitting Transistor: p‐Type Porous Silicon Nanowire/n‐Type ZnO Nanofilm

An inorganic nano light‐emitting transistor (INLET) consisting of p‐type porous Si nanowires (PoSiNWs) and an n‐type ZnO nanofilm was integrated on a heavily doped p‐type Si substrate with a thermally grown SiO₂ layer. To verify that modulation of the Fermi level of the PoSiNWs is key for switchable light emitting, I–V and electroluminescent characteristics of the INLET are investigated as a function of gate bias (V _g). As the V _g is changed from 0 V to ?20 V, the current level and light‐emission intensity in the orange–red range increase by three and two times, respectively, with a forward bias of 20 V in the p–n junction, compared to those at a V _g of 0 V. On the other hand, as the V _g approaches 10 V, the current level decreases and the emission intensity is reduced and then finally switched off. This result arises from the modulation of the Fermi level of the PoSiNWs and the built‐in potential at the p–n junction by the applied gate electric field.     

Charge‐Trap Memory Based on Hybrid 0D Quantum Dot–2D WSe2 Structure

Recently, layered ultrathin 2D semiconductors, such as MoS₂ and WSe₂ are widely studied in nonvolatile memories because of their excellent electronic properties. Additionally, discrete 0D metallic nanocrystals and quantum dots (QDs) are considered to be outstanding charge‐trap materials. Here, a charge‐trap memory device based on a hybrid 0D CdSe QD–2D WSe₂ structure is demonstrated. Specifically, ultrathin WSe₂ is employed as the channel of the memory, and the QDs serve as the charge‐trap layer. This device shows a large memory window exceeding 18 V, a high erase/program current ratio (reaching up to 10⁴), four‐level data storage ability, stable retention property, and high endurance of more than 400 cycles. Moreover, comparative experiments are carried out to prove that the charges are trapped by the QDs embedded in the Al₂O₃. The combination of 2D semiconductors with 0D QDs opens up a novelty field of charge‐trap memory devices.     

Semiconductor‐Nanocrystals‐Based White Light‐Emitting Diodes

In response to the demands for energy and the concerns of global warming and climate change, energy efficient and environmentally friendly solid‐state lighting, such as white light‐emitting diodes (WLEDs), is considered to be the most promising and suitable light source. Because of their small size, high efficiency, and long lifetime, WLEDs based on colloidal semiconductor nanocrystals (or quantum dots) are emerging as a completely new technology platform for the development of flat‐panel displays and solid‐state lighting, exhibiting the potential to replace the conventionally used incandescent and fluorescent lamps. This replacement can cut the ever‐increasing level of energy consumption, solve the problem of rapidly depleting fossil fuel reserves, and improve the quality of the global environment. In this review, the recent progress in semiconductor‐nanocrystals‐based WLEDs is highlighted, the different approaches for generating white light are compared, and the benefits and challenges of the solid‐state lighting technology are discussed.     

Next‐Generation Narrow‐Band Green‐Emitting RbLi(Li3SiO4)2:Eu2+ Phosphor for Backlight Display Application

The discovery of high efficiency narrow‐band green‐emitting phosphors is a major challenge in backlighting light‐emitting diodes (LEDs). Benefitting from highly condensed and rigid framework structure of UCr₄C₄‐type compounds, a next‐generation narrow green emitter, RbLi(Li₃SiO₄)₂:Eu²⁺ (RLSO:Eu²⁺), has emerged in the oxide‐based family with superior luminescence properties. RLSO:Eu²⁺ phosphor can be efficiently excited by GaN‐based blue LEDs, and shows green emission at 530 nm with a narrow full width at half maximum of 42 nm, and very low thermal quenching (103%@150 °C of the integrated emission intensity at 20 °C), however its chemical stability needs to be improved later. The white LED backlight using optimized RLSO:8%Eu²⁺ phosphor demonstrates a high luminous efficacy of 97.28 lm W^?1 and a wide color gamut (107% National Television System Committee standard (NTSC) in Commission Internationale de L'Eclairage (CIE) 1931 color space), suggesting its great potential for industrial applications as liquid crystal display (LCD) backlighting.     

Lead Halide Post‐Perovskite‐Type Chains for High‐Efficiency White‐Light Emission

Hybrid metal halides containing perovskite layers have recently shown great potential for applications in solar cells and light‐emitting diodes. Such compounds exhibit quantum confinement effects leading to tunable optical and electronic properties. Thus, broadband white‐light emission has been observed from diverse metal halides and, owing to high color rendering index, high thermal stability, and low‐temperature solution processability, these materials have attracted interest for application in solid‐state lighting. However, the reported quantum yields for white photoluminescence (PLQY) remain low (i.e., in the range 0.5–9%) and no approach has shown to successfully increase the intensity of this emission. Here, it is demonstrated that the quantum efficiencies of hybrid metal halides can be greatly enhanced if they contain a polymorph of the [PbX₄]^2? perovskite‐type layers: the [PbX₄]^2? post‐perovskite‐type chains showing a PLQY of 45%. Different piperazines lead to a hybrid lead halide with either perovskite layers or post‐perovskite chains influencing strongly the presence of self‐trapped states for excitons. It is anticipated that this family of hybrid lead halide materials could enhance all the properties requiring the stabilization of trapped excitons.     

Molybdenum Disulfide Nanosheet/Quantum Dot Dynamic Memristive Structure Driven by Photoinduced Phase Transition

MoS₂ 2D nanosheets (NS) with intercalated 0D quantum dots (QDs) represent promising structures for creating low‐dimensional (LD) resistive memory devices. Nonvolatile memristors based 2D materials demonstrate low power consumption and ultrahigh density. Here, the observation of a photoinduced phase transition in the 2D NS/0D QDs MoS₂ structure providing dynamic resistive memory is reported. The resistive switching of the MoS₂ NS/QD structure is observed in an electric field and can be controlled through local QD excitations. Photoexcitation of the LD structure at different laser power densities leads to a reversible MoS₂ 2H‐1T phase transition and demonstrates the potential of the LD structure for implementing a new dynamic ultrafast photoresistive memory. The dynamic LD photomemristive structure is attractive for real‐time pattern recognition and photoconfiguration of artificial neural networks in a wide spectral range of sensitivity provided by QDs.     

Phosphorus‐Mediated MoS2 Nanowires as a High‐Performance Electrode Material for Quasi‐Solid‐State Sodium‐Ion Intercalation Supercapacitors

Molybdenum disulfide (MoS₂) is a promising electrode material for electrochemical energy storage owing to its high theoretical specific capacity and fascinating 2D layered structure. However, its sluggish kinetics for ionic diffusion and charge transfer limits its practical applications. Here, a promising strategy is reported for enhancing the Na⁺‐ion charge storage kinetics of MoS₂ for supercapacitors. In this strategy, electrical conductivity is enhanced and the diffusion barrier of Na⁺ ion is lowered by a facile phosphorus‐doping treatment. Density functional theory results reveal that the lowest energy barrier of dilute Na‐vacancy diffusion on P‐doped MoS₂ (0.11 eV) is considerably lower than that on pure MoS₂ (0.19 eV), thereby signifying a prominent rate performance at high Na intercalation stages upon P‐doping. Moreover, the Na‐vacancy diffusion coefficient of the P‐doped MoS₂ at room temperatures can be enhanced substantially by approximately two orders of magnitude (10^?6–10^?4 cm² s^?1) compared with pure MoS₂. Finally, the quasi‐solid‐state asymmetrical supercapacitor assembled with P‐doped MoS₂ and MnO₂, as the positive and negative electrode materials, respectively, exhibits an ultrahigh energy density of 67.4 W h kg^?1 at 850 W kg^?1 and excellent cycling stability with 93.4% capacitance retention after 5000 cycles at 8 A g^?1.     

Gap‐Mode Surface‐Plasmon‐Enhanced Photoluminescence and Photoresponse of MoS2

2D materials hold great potential for designing novel electronic and optoelectronic devices. However, 2D material can only absorb limited incident light. As a representative 2D semiconductor, monolayer MoS₂ can only absorb up to 10% of the incident light in the visible, which is not sufficient to achieve a high optical‐to‐electrical conversion efficiency. To overcome this shortcoming, a “gap‐mode” plasmon‐enhanced monolayer MoS₂ fluorescent emitter and photodetector is designed by squeezing the light‐field into Ag shell‐isolated nanoparticles–Au film gap, where the confined electromagnetic field can interact with monolayer MoS₂. With this gap‐mode plasmon‐enhanced configuration, a 110‐fold enhancement of photoluminescence intensity is achieved, exceeding values reached by other plasmon‐enhanced MoS₂ fluorescent emitters. In addition, a gap‐mode plasmon‐enhanced monolayer MoS₂ photodetector with an 880% enhancement in photocurrent and a responsivity of 287.5 A W^?1 is demonstrated, exceeding previously reported plasmon‐enhanced monolayer MoS₂ photodetectors.     

Synthesis and characterisation of MoS2 quantum dots by liquid nitrogen quenching

Among transition metal dichalcogenides family, molybdenum disulphide (MoS₂) nanomaterial has a vital role in two-dimensional field due to its intrinsic optical and electronic properties. In this study, we report a new top-down approach for synthesising MoS₂ quantum dots (QDs). This strategy consists of liquid nitrogen (LN2) quenching of bulk MoS₂ material followed by two processes, probe sonication and ultra-centrifugation. This approach is simple, cost effective and eco-friendly. The structural, optical and morphological properties of obtained MoS₂ quantum dots were characterised. Photoluminescence spectra (PL) of the synthesised MoS₂ QDs show blue light emission when excited with ultraviolet radiation (365?nm). A significant observation in this study is that, the peak position of photoluminescence (PL) emission spectra is independent of excitation wavelength. In addition, a higher fluorescence quantum yield was obtained for the present MoS₂ QDs compared to MoS₂ QDs prepared by other methods.     

NIR‐Emitting Quantum Dot‐Encoded Microbeads through Membrane Emulsification for Multiplexed Immunoassays

NIR‐emitting CdSeTe/CdS/ZnS core/shell/shell QD‐encoded microbeads are combined with common flow cytometry with one laser for multiplexed detection of hepatitis B virus (HBV). A facile one‐pot synthetic route is developed to prepare CdSeTe/CdS/ZnS core/shell/shell QDs with high photoluminescence quantum yield and excellent stability in liquid paraffin, and a Shirasu porous glass (SPG) membrane emulsification technique is applied to incorporate the QDs into polystyrene–maleic anhydride (PSMA) microbeads to obtain highly fluorescent QD‐encoded microbeads. The relatively wide NIR photoluminescence full width half maximum of the CdSeTe/CdS/ZnS QDs is used to develop a ‘single wavelength’ encoding method to obtain different optical codes by changing the wavelengh and emission intensity of the QDs incorporated into the microbeads. Moreover, a detection platform combining NIR‐emitting CdSeTe/CdS/ZnS QD‐encoded microbeads and Beckman Coulter FC 500 flow cytometry with one laser of 488 nm is successfully used to conduct a 2‐plex hybridization assay for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), and a 3‐plex hybridization assay for hepatitis B surface antibody (HBsAb), hepatitis B e antibody (HBeAb), and hepatitis B core antibody (HBcAb), which suggests the promising application of NIR QD‐encoded microbeads for multiplex immunoassays.     

All‐Inorganic CsCu2I3 Single Crystal with High‐PLQY (≈15.7%) Intrinsic White‐Light Emission via Strongly Localized 1D Excitonic Recombination

Energy‐saving white lighting from the efficient intrinsic emission of semiconductors is considered as a next‐generation lighting source. Currently, white‐light emission can be composited with a blue light‐emitting diode and yellow phosphor. However, this solution has an inevitable light loss, which makes the improvement of the energy utilization efficiency more difficult. To deal with this problem, intrinsic white‐light emission (IWE) in a single solid material gives a possibility. Here, an all‐inorganic lead‐free CsCu₂I₃ perovskite single crystal (SC) with stable and high photoluminescence quantum yield (≈15.7%) IWE through strongly localized 1D exciton recombination is synthesized. In the CsCu₂I₃, the Cu–I octahedron, which provides most of electron states, is isolated by Cs atoms in two directions to form a 1D electronic structure, resulting a high radiation recombination rate of excitons. With this electronic structure design, the CsCu₂I₃ SCs have great potential in energy‐saving white lighting.     

Near-infrared-emitting colloidal Ag<Subscript>2</Subscript>S quantum dots excited by an 808 nm diode laser

Thioglycolic acid (TGA)-coated colloidal Ag₂S quantum dots (QDs) emitting in the near-infrared (NIR) region upon excitation by an 808 nm diode laser were synthesized. The observed photoluminescence (PL) was attributed to the presence of ligand-modified Ag₂S on the QD surfaces and could be easily controlled by a simple dilution process due to the concentration-dependent surface structure of the colloidal QDs. Upon dilution of the solution, the PL intensity initially increased before later decreasing, with a blueshift being observed in the PL spectra. These phenomena can be accounted for by the aggregation of QDs due to a decrease in the content of ligand-modified Ag₂S on the QD surfaces upon dilution, which in turn affected the fluorescence resonance energy transfer (FRET), and re-emission of the surface energy level.