Ⅰ-Ⅲ-Ⅵ chalcogenide semiconductor nanocrystals:Synthesis,properties,and applications

Colloidal semiconductor nanocrystals have been proven to be promising candidates for applications in low‐cost and high‐performance photovoltaics,bioimaging,and photocatalysis due to their novel size‐and shape‐dependent properties.Among the colloidal systems,I‐III‐VI semiconductor nanocrystals(NCs)have drawn much attention in the past few decades.Compared to binary NCs,ternary I‐III‐VI NCs not only exhibit low toxicity,but also a high performance similar to that of binary NCs.In this review,we mainly focus on the synthesis,properties,and applications of I‐III‐VI NCs.We summarize the major synthesis methods,analyze their photophysical and electronic properties,and highlight some of the latest applications of I‐III‐VI NCs in solar cells,light‐emitting diodes,bioimaging,and photocatalysis.Finally,based on the information reviewed,we highlight the existing problems and challenges.

Lensless opto-electronic neural network with quantum dot nonlinear activation

With the swift advancement of neural networks and their expanding applications in many fields, optical neural networks have gradually become a feasible alternative to electrical neural networks due to their parallelism, high speed, low latency, and power consumption. Nonetheless, optical nonlinearity is hard to realize in free-space optics, which restricts the potential of the architecture.

Overcoming side reaction effects in the colloidal synthesis of ZnSe/ZnS core/shell quantum dots with an etching strategy

The potential use of large-size ZnSe quantum dots as blue emitters for display applications has greatly inspired the colloidal synthesis.Herein,we report the negative effects of side reactions of large-size ZnSe quantum dots.The side reactions between oleic acid and oleylamine generated amidation products and H_(2)O,which led to the hydrolysis of Zn(OA)2 to Zn(OH)2 and the subsequent formation of zinc oxide(ZnO)and zinc bis[diphenylphosphinate](Zn(DPPA)2)precipitates.These side reactions resulted in the formation of a defective surface including a Se-rich surface and oxygen-related defects.Such negative effects can be overcome by adopting an etching strategy using potassium fluoride and myristic acid in combination.By overcoating a ZnS shell,blue emissive ZnSe/ZnS quantum dots with a maximum photoluminescence quantum yield of up to 91%were obtained.We further fabricated ZnSe quantum dots-based blue light-emitting diodes with an emission peak at 456 nm.The device showed a turn-on voltage of 2.7 V with a maximum external quantum efficiency of 4.2%and a maximum luminance of 1223 cd·m^(−2).

Pure-blue emissive ZnSe/Cd_(x)Zn_(1-x)S/ZnS quantum dots with type-II core-shell structure for display application

Blue emissive quantum dots are key materials in fabricating quantum-dot light-emitting diodes for display applications.Up to date,most of the previous blue emissive quantum dots are based on quantum dots with type-I core-shell structure.In this work,we report pure-blue emissive ZnSe/Cd_(x)Zn_(1-x)S/ZnS quantum dots with type-II core-shell structure,which show high photoluminescence quantum yield over 90%.The type-II structure was investigated by applying time-resolved photoluminescence and transient absorption measurements,illustrating the extended photoluminescence decay lifetime of ZnSe/Cd_(x)Zn_(1-x)S quantum dots as well as the transition of bleaching peak from the valence band of ZnSe to the conduction band of CdZnS.We further fabricated ZnSe/Cd_(x)Zn_(1-x)S/ZnS quantum dots based electroluminescence devices,achieving a maximum external quantum efficiency of 6.7%and a maximum luminance of 39,766 cd·m^(-2).

Revealing the vertical structure of in-situ fabricated perovskite nanocrystals films toward efficient pure red light-emitting diodes

The development of efficient perovskite light-emitting diodes(PeLEDs)relies strongly on the fabrication of perovskite films with rationally designed structures(grain size,composition,surface,etc.).Therefore,an understanding of structure-performance relationships is of vital importance for developing high-performance perovskite devices,particularly for devices with in-situ fabricated perovskite nanocrystal films.In this study,we reveal the vertical structure of an in-situ fabricated quasi-two-dimensional perovskite film.By combining time-of-flight secondary ion mass spectrometry,energy dispersive spectroscopy,grazing incidence wide-angle X-ray scattering(GIWAXS),and low-temperature photoluminescence spectra,we illustrate that the resulting in-situ fabricated DPPA_(2)Cs_(n-1)Pb_(n)(Br_(0.3)I_(0.7))_(3n+1)(DPPA^(+):3,3-diphenylpropylammonium)film has a gradient structure with a very thin layer of ligands on the surface,predominantly small-n domains at the top,and predominantly large-n domains at the bottom owing to the solubility difference of the precursors.In addition,GIWAXS measurements show that the domain of n=2 on the top layer has an ordered in-plane alignment.Based on the understanding of the film structure,we developed an in-situ fabrication process with ligand exchange to achieve efficient pure red PeLEDs at 638 nm with an average external quantum efficiency(EQE)of 7.4%.The optimized device had a maximum luminance of 623 cd/m^(2) with a peak EQE of 9.7%.

Highly efficient and stable white LEDs based on pure red narrow bandwidth emission triangular carbon quantum dots for wide-color gamut backlight displays

High-performance white light-emitting diodes (WLEDs) hold great potential for the next-generation backlight display applications.However,achieving highly efficient and stable WLEDs with wide-color-gamut has remained a formidable goal.Reported here is the first example of pure red narrow bandwidth emission triangular CQDs (PR-NBE-T-CQDs) with photoluminescence peaking at 610 nm.The PR-NBE-T-CQDs synthesized from resorcinol show high quantum yield (QY) of 72% with small full width at half maximum of 33 nm.By simply controlling the reaction time,pure green (PG-) NBE-T-CQDs with high QY of 75% were also obtained.Highly efficient and stable WLEDs with wide-color-gamut based on PR- and PG-NBE-T-CQDs was achieved.This WLED showed a remarkable wide-color gamut of 110% NTSC and high power efficiency of 86.5 lumens per Watt.Furthermore,such WLEDs demonstrate outstanding stability.This work will set the stage for developing highly efficient,low cost and environment-friendly WLEDs based on CQDs for the next-generation wide-color gamut backlight displays.

Halide perovskite quantum dots: potential candidates for display technology

Motivated by the color tunability and narrow-band emission peak of colloidal quantum dots(QDs),the concepts of quantum dot light-emitting diodes(QD-LEDs),based on either the photoluminescence(PL)or electroluminescence(EL)mechanism,have been proposed for a few years[1].Using QD-LEDs in the backlighting system of liquid crystal display(LCD)can significantly expand the

In-situ fabricated anisotropic halide perovskite nanocrystals in polyvinylalcohol nanofibers: Shape tuning and polarized emission

We report an in-situ fabrication of halide perovskite (CH3NH3PbX3,CH3NH3 =methylammonium,MA,X =Cl,Br,I) nanocrystals in polyvinylalcohol (PVA) nanofibers (MAPbX3@PVA nanofibers) through electrospinning a perovskite precursor solution.With the content of the precursors increased,the resulting MAPbBr3 nanocrystals in PVA matrix changed the shape from ellipsoidal to pearl-like,and finely into rods-like.Optimized MAPbBr3@PVA nanofibers show strong polarized emission with the photoluminescence quantum yield of up to 72%.We reveal correlations between the shape of in-situ fabricated perovskite nanocrystals and the polarization degree of their emission by comparing experimental data from the single nanofiber measurements with theoretical calculations.Polarized emission of MAPbBr3@PVA nanofibers can be attributed to the dielectric confinement and quantum confinement effects.Moreover,nanofibers can be efficiently aligned by using parallel positioned conductor strips with an air gap as collector.A polarization ratio of 0.42 was achieved for the films of well-aligned MAPbBr3@PVA nanofibers with a macroscale size of 0.5 cm × 2 cm,which allows potential applications in displays,lasers,waveguides,etc.

Broadband perovskite quantum dot spectrometer beyond human visual resolution

The quantum dot spectrometer,fabricated by integrating different quantum dots with an image sensor to reconstruct the target spectrum from spectral-coupled measurements,is an emerging and promising hyperspectrometry technology with high resolution and a compact size.The spectral resolution and spectral range of quantum dot spectrometers have been limited by the spectral variety of the available quantum dots and the robustness of algorithmic reconstruction.Moreover,the spectrometer integration of quantum dots also suffers from inherent photoluminescence emission and poor batch-to-batch repeatability.In this work,we developed nonemissive in situ fabricated MA_(3)Bi_(2)X_(9) and Cs_(2)SnX_(6)(MA=CH_(3)NH_(3);X=Cl,Br,I)perovskite-quantum-dot-embedded films(PQDFs)with precisely tunable transmittance spectra for quantum dot spectrometer applications.The resulting PQDFs contain in situ fabricated perovskite nanocrystals with homogenous dispersion in a polymeric matrix,giving them advantageous features such as high transmittance efficiency and good batch-to-batch repeatability.By integrating a filter array of 361 kinds of PQDFs with a silicon-based photodetector array,we successfully demonstrated the construction of a perovskite quantum dot spectrometer combined with a compressive-sensing-based total-variation optimization algorithm.A spectral resolution of ~1.6 nm was achieved in the broadband of 250-1000 nm.The performance of the perovskite quantum dot spectrometer is well beyond that of human eyes in terms of both the spectral range and spectral resolution.This advancement will not only pave the way for using quantum dot spectrometers for practical applications but also significantly impact the development of artificial intelligence products,clinical treatment equipment,scientific instruments,etc.

Enhanced piezo-response in copper halide perovskites based PVDF composite films

ln-situ fabricated perovskite nanocrystals in polymeric matrix provide new generation composite mate- rials for plenty of cutting edge technology. In this work, we report the in-situ fabrication of copper halide perovskite （MA_2CuCI_4, MA：CH_3NH＋3） embedded poly（vinylidene fluoride） （PVDF） composite films. The optimized MA_2CuCI_4/PVDF composite films exhibit greatly enhanced piezo-response in comparasion with pure PVDF films. The enhancements were invesitgated and explained by applying piezo-response force microscopy （PFM） measurements and density functional theory （DFT） caculations. We proposed that the high piezoelectric properties of MA_2CuCI_4/PVDF composite films could be related to the large Cu off-centering displacement, the strong interactions between MA_2CuCI_4 and PVDF as well as large stress concentration around the MA_2CuCI_4 particles in the films. These piezoelectric composite films are expected to be suitable functional materials for flexible and/or wearable niezoelectrics.

Perovskite quantum dot microarrays:In situ fabrication via direct print photopolymerization

Quantum dots color conversion(QDCC)is considered as a facial and versatile way to achieve full-color organic light emitting diode(OLED)and micro-LED display due to the wide color gamut performance and easy integration.However,the aggregation of QDs and coffee-ring effects after solvent evaporation lowers the light conversion efficiency and emission uniformity in QDs microarrays,raising blue-light leakage or optical crosstalk.Here,we report the fabrication of perovskite quantum dots(PQDs)microarrays by combining the inkjet printing and in situ fabrication of PQDs during the photopolymerization of precursor ink.The resulting PQDs microarrays exhibit three-dimensional(3D)morphology with hemisphere shape as well as strong photoluminescence,which is desirable for QDCC applications.We demonstrate the dominant role of ultraviolet(UV)curable precursors and surface functionalized substrate in controlling the shape of microarrays,where significantly increased contact angle(100°)and large height to diameter ratio(0.42)can be achieved.We further demonstrate the potential use of the in situ direct print photopolymerization method for fabricating large-area multicolor patterned pixel microarrays with a wide color gamut and high resolution.The fabrication of 3D PQDs microarrays opens up new opportunities in a variety of applications including photonics integration,micro-LED,and near-field display.

Nonlocal interaction enhanced biexciton emission in large CsPbBr_(3) nanocrystals

Biexciton emission in quantum dots is an efficient way to generate entangled photon pairs,which are key resources in quantum informatics.Compared with epitaxial grown quantum dots,chemically synthesized colloidal quantum dots show advantages of tunable wavelength and easy integration to realize quantum light sources.However,biexciton efficiency of colloidal quantum dots has been limited by Auger recombination.In this paper,we reported nonlocal interaction enhanced biexciton emission with efficiency up to 80% in large perovskite nanocrystals(>20 nm).The nonlocal interaction between carriers and excitons leads to the abnormal exponential decrease of Auger recombination with volume in large nanocrystals,which distinguishes with the linear scaling in small counterparts.Such an exponential decrease of Auger recombination results in long lifetime of biexcitons,responsible for the required high biexciton efficiency.The discovery of nonlocal effects in large semiconductor nanocrystals provides new strategies to achieve high efficiency multiple excitons for quantum optics and energy conversation applications.

Progress in semiconductor quantum dots-based continuous-wave laser

Continuous-wave(CW)operated laser is a key component for photonic chips.It has been highly desired to develop low-threshold,high-efficiency,long-term operational,low-cost and easily integratable CW laser.As excellent optical gain materials,quantum dots(QDs)have been intensively investigated for on-chip CW lasers owing to their high photoluminescence quantum yields,tunable emission wavelengths and easy integration.Base on the difference of preparation processes,QDs can be classified into epitaxial QDs and solution-processed colloidal QDs(CQDs).In this mini-review,we summarize the research progresses of epitaxial III–V semiconductor QD and solution-processed CQD-based CW lasers.The challenges associated with the realization of CQD CW lasers are discussed in detail.In particular,the emerging perovskite-based CW lasers are highlighted.Finally,a short perspective of QD-based CW lasers is presented.

Full degree-of-freedom polarization hologram by freeform exposure and inkjet printing

Since the invention of holography by Dennis Gabor,the fabrication of holograms has mainly relied on direct recording of wavefront by engraving the intensity fringes of interfering electric fields into the holographic material.The degree-of-freedom(DoF)is often limited,especially for its usage as a holographic optical element in imaging or display systems,as what is recorded is what to use.In this work,based on the emerging self-assembled photo-aligned liquid crystal,a polarization hologram with full DoF for local manipulation of optical structure is demonstrated.The ability to record an arbitrary wavefront(in-plane DoF)is achieved by freeform surface exposure,while the local adjustment of deposited liquid crystal(out-of-plane DoF)is realized by inkjet printing.The methodology for designing and fabricating such a hologram is exemplified by building a full-color retinal scanning display without color crosstalk.Here,the arbitrary wavefront modulation capability helps to eliminate the aberrations caused by mismatched exposure and display wavelengths.The local liquid crystal adjustment ability enables the suppression of crosstalk by variation of chiral pitch and film thickness to tune the peak and valley of Bragg diffraction band.The demonstrated method is expected to greatly impact the fields of advanced imaging and display,such as augmented reality and virtual reality,that require optics with an ultrathin form factor and high degrees of design freedom simultaneously.

Broadband mid-IR antireflective Reuleaux-triangle-shaped hole array on germanium

A gradient-index Reuleaux-triangle-shaped hole array was fabricated on germanium(Ge)by nanoimprint lithography and inductively coupled plasma processing as a broadband mid-infrared(IR)antireflective surface.The interaction between the{111}planes of cubic crystalline Ge and a circular mold successfully produced an orderly and periodically distributed Reuleaux-triangle-shaped hole array.As a result,the average transmittance increased 15.67% over the waveband at 3–12μm and remained stable at the incidence angle of up to 60°.The vertices of the Reuleaux triangle showed local enhancement of the electric field intensities due to interference of the incident and reflected radiation fields.It was also found that nonuniform hole depths acted to modulate the transmittance over the 3–12μm waveband.

Erratum to:Highly efficient and stable white LEDs based on pure red narrow bandwidth emission triangular carbon quantum dots for wide-color gamut backlight displays

In the version of this article originally published,Figs.2(d)and 3(a),and Figs.S3 and S6 in the Electronic Supplementary Material(ESM)were incorrect.The corrected images are shown below.

Detour-phased perovskite ultrathin planar lens using direct femtosecond laser writing

Perovskite-enabled optical devices have drawn intensive interest and have been considered promising candidates for integrated optoelectronic systems.As one of the important photonic functions,optical phase modulation previously was demonstrated with perovskite substrate and complex refractive index engineering with laser scribing.Here we report on the new scheme of achieving efficient phase modulation by combining detour phase design with 40 nm ultrathin perovskite films composed of nanosized crystalline particles.Phase modulation was realized by binary amplitude patterning,which significantly simplifies the fabrication process.Perovskite nanocrystal films exhibit significantly weak ion migration effects under femtosecond laser writing,resulting in smooth edges along the laser ablated area and high diffractive optical quality.Fabrication of a detour-phased perovskite ultrathin planar lens with a diameter of 150μm using femtosecond laser scribing was experimentally demonstrated.A high-performance 3D focus was observed,and the fabrication showed a high tolerance with different laser writing powers.Furthermore,the high-quality imaging capability of perovskite ultrathin planar lenses with a suppressed background was also demonstrated.

Breaking the symmetry of colloidal 2D nanoplatelets:Twist induced quantum coupling

Twist provides a new degree of freedom for nanomaterial modifications,which can provide novel physical properties.Here,colloidal two-dimensional(2D)twisted CdSe nanoplatelets(NPLs)are successfully fabricated and their morphology can change from totally flat to edge-twisted,and then to middle-twisted with prolonged reaction time.By combining experiments and corresponding theoretical analyses,we have established the length-dependent relationships between the surface energy and twist,with a critical lateral dimension of 30 nm.We found that the defects formed during the synthesis process play a vital role in generating intense stress that develops a strong torsion tensor around the edges,resulting in edge-twisted and final middletwisted NPLs.Furthermore,due to the geometric asymmetry of twisted NPLs,the dissymmetry factor of single particle NPLs can reach up to 0.334.Specifically,quantum coupling occurs in middle-twisted NPLs by twisting one parent NPL into two daughter NPLs,which are structurally and electronically coupled.This work not only further deepens our understanding of the twist mechanism of 2D NPLs during colloidal synthesis,but also opens a pathway for applications using twistronics and quantum technology.

Excitation-dependent perovskite/polymer films for ultraviolet visualization

Ultraviolet(UV)visualization has extensive applications in military and civil fields such as security monitoring,space communication,and wearable equipment for health monitoring in the internet of things(IoT).Due to their remarkable optoelectronic features,perovskite materials are regarded as promising candidates for UV light detecting and imaging.Herein,we report for the first time the excitationdependent perovskite/polymer films with dynamically tunable fluorescence ranging from green to magenta by changing the UV excitation from 260 to 380 nm.And they still render dynamic multicolor UV light imaging with different polymer matrixes,halogen ratios,and cations of perovskite materials.The mechanism of its fluorescence change is related to the chloride vacancies in perovskite materials.A patterned multi-color ultraviolet visualization pad is also demonstrated for visible conversion of the UV region.This technique may provide a universal strategy for information securities,UV visualizations,and dynamic multi-color displays in the IoT.

A general methodology to measure the light-to-heat conversion efficiency of solid materials

Light-to-heat conversion has been intensively investigated due to the potential applications including photothermal therapy and solar energy harvesting.As a fundamental property of materials,accurate measurement of light-to-heat conversion efficiency(LHCE)is of vital importance in developing advanced materials for photothermal applications.Herein,we report a photothermal and electrothermal equivalence(PEE)method to measure the LHCE of solid materials by simulating the laser heating process with electric heating process.The temperature evolution of samples during electric heating process was firstly measured,enabling us to derive the heat dissipation coefficient by performing a linear fitting at thermal equilibrium.The LHCE of samples can be calculated under laser heating with the consideration of heat dissipation coefficient.We further discussed the effectiveness of assumptions by combining the theoretical analysis and experimental measurements,supporting the obtained small error within 5%and excellent reproducibility.This method is versatile to measure the LHCE of inorganic nanocrystals,carbon-based materials and organic materials,indicating the applicability of a variety of materials.