Entire Visible Spectrum Research Articles

Real-time observation of ion exchange dynamics during surface treatment of all-inorganic perovskite quantum dots with Zn-halogenide complexes for color tuning and enhanced quantum efficiency.

All-inorganic lead perovskite quantum dots (QDs), due to their distinctive optical properties, have become one of the "hottest" topics in materials science; therefore, the development of new QD synthesis methods or their emission color adjustment is of great interest. Within this study, we present the simple preparation of QDs employing a novel ultrasound-induced hot-injection method, which significantly reduces the QD synthesis time from several hours to merely 15-20 minutes. Moreover, the post-synthesis treatment of perovskite QDs in solutions using zinc halogenide complexes could increase the QD emission intensity and, at the same time, boost their quantum efficiency. This behavior is due to the zinc halogenide complex's ability to remove or significantly reduce the number of surface electron traps in perovskite QDs. Finally, the experiment that shows the ability to instantly adjust the desired emission color of perovskite QDs by variation of the amount of added zinc halogenide complex is presented. The instantly obtained perovskite QD colors cover virtually the full range of the visible spectrum. The zinc halogenide modified perovskite QDs exhibit up to 10-15% higher QEs than those prepared by an individual synthesis.

Push-pull [7]helicene diimide: excited-state charge transfer and solvatochromic circularly polarised luminescence.

In this communication we describe a helically chiral push-pull molecule named 9,10-dimethoxy-[7]helicene diimide, displaying fluorescence (FL) and circularly polarised luminescence (CPL) over nearly the entire visible spectrum dependent on solvent polarity. The synthesised molecule exhibits an unusual solvent polarity dependence of FL quantum yield and nonradiative rate constant, as well as remarkable gabs and glum values along with high configurational stability.

Controlled LED Lighting for Horticulture: A Review

As energy gradually becomes a more valuable commodity, the desire for reduced energy losses strengthens. Lighting is a critical field on this matter, as it accounts for a large percentage of the global electricity consumption and modern lighting systems are greatly more efficient than incandescent, discharge, and fluorescent lights. Previous research has proven that plants do not require the entire visible spectrum but react only to specific wavelengths, making it possible to control their growth and yield via artificial lighting. The flexibility of control of Light Emitting Diode (LED) lights allows for the combination of great energy losses reduction and controlled plant growth, achieving the improvement of two major parameters in a single action. This review paper summarizes the current research on the effect different light wavelengths have on specific plant species and discusses the applications of LED lighting for horticulture, yield storage, and disease protection.

Ultrasound-activated luminescence with color tunability enabled by mechanoluminescent colloids and perovskite quantum dots.

Ultrasound represents a wireless and non-contact route for energy delivery and device control, owing to its ability to propagate and focus in various mediums including biological tissue. Specifically, ultrasound-activated mechanoluminescence from a colloidal suspension of mechanoluminescent (ML) nanocrystals offers a wireless means to remotely control a light source, such as wirelessly addressing a multicolor display. However, the limited color purity and tunability, as well as the large sizes of conventional ML materials prevent their use in an ultrasound-mediated flexible color display. Here, we apply a biomineral-inspired suppressed dissolution approach to synthesize ML colloids with bright blue emission under ultrasound and small sizes down to 20 nm. In addition, we leverage the bandgap engineering strategy of all-inorganic perovskite quantum dots (PQDs) to achieve wavelength tunability of the mechanoluminescence of ML colloid/PQD composites. Remarkably, the ultrasound-activated emission of the ML colloid/PQD composites exhibits a highly saturated color gamut covering the entire visible spectrum. Based on these advantages, we assembled a pixel array composed of different ML colloid/PQD composites in a silicone elastomer and demonstrated the proof-of-concept of a flexible and wireless multicolor display with each pixel individually addressed by scanning focused ultrasound.

Thermo- and electrochromic smart window derived from a viologen-tethered triazolum based poly(NIPAmn-TEG-BPV) electrolyte to enhance building energy efficiency and visual comfort

In this work, we synthesized by facilely incorporating a modified asymmetric viologen onto the triazole moiety of a phase-changing monomer [poly(NIPAmn-TEG)] via quaternization to produce dual-responsive material [poly(NIPAmn-TEG-BPV)]. However, most chromic material-based smart windows have responded to only one stimulus, but studies on dual-responsive windows are to be given more attention due to the many opportunities in terms of utility and activity that they offer. Whereas here in our work apart from being electrochromic, the material is thermochromic as well, switching from clean to opaque at when heated from 25 to 32 °C as a result of phase transformation, attaining >84.7 % optical contrast (ΔT) in the visible range (650 nm). Similar results were obtained while switching from a clear state to a purple state at an applied potential of ∼ 2.5 V which gave an optical contrast of (ΔT) >89.6 % (550 nm). A coloration speed of 8.1 s and bleaching speed of 26.1 s were attained by the poly(NIPAmn-TEG-BPV) with a coloration efficiency of 346 cm2C−1 and cyclic stability of >500 cycles. The synergistic effect of its thermochromic and electrochromic response when stimulated simultaneously, showed a transparent state to a cloudy blue state and gave high (ΔT) >91.05 % with full absorption of the entire visible solar spectrum resulting to a truly blue opaque state that is ideal for building façade requiring absolute privacy.

Fabrication and Characterization of Si/PEDOT: PSS-Based Heterojunction Solar Cells

In this study, we fabricated a planar Si/PEDOT: PSS heterojunction solar cell using three different solvents—ethylene glycol, acetonitrile, and dimethyl sulfoxide—to find the best one. The fabricated samples were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, X-ray diffraction, and current–voltage. Diffused reflectance spectrum analysis showed reduced reflectance compared to the bare silicon wafers. The absorbance spectrum shows the change in absorption of the Si-coated PEDOT: PSS which was more than a 50% increase in the UV region, and for the EG sample, there was a 20% increase in the entire visible spectrum. This indicates that the solvent plays a major role in the bandgap between the Si and Si/PEDOT: PSS. Scanning electron microscope (SEM) was used to examine the surface morphology of Si/PEDOT: PSS as agglomerated, island-formed surfaces and carbon-layered Si-PEDOT: PSS. Cross-sectional images show the thickness of the PEDOT: PSS layer on the silicon wafer surface. The X-ray diffraction (XRD) pattern shows the characteristic peaks for silicon (69.5°), and Si/PEDOT: PSS shows a forbidden Si (200) peak at 32°. Current–voltage measurements have shown the characteristic diode curve for all fabricated cells. This characteristic diode curve indicated the presence of a heterojunction. Ethylene glycol-containing cells showed current output as 0.2 μA with Voc of 0.2 V.

Robust Full-Spectral Color Tuning of Photonic Colloids.

Creation of color through photonic morphologies manufactured by molecular self-assembly is a promising approach, but the complexity and lack of robustness of the fabrication processes have limited their technical exploitation. Here, it is shown that photonic spheres with full-color tuning across the entire visible spectrum can be readily and reliably achieved by the emulsification of solutions containing a block copolymer (BCP) and two swelling additives. Solvent diffusion out of the emulsion droplets gives rise to 20-150µm-sized spheres with an onion-like lamellar morphology. Controlling the lamellar thickness by differential swelling with the two additives enables color tuning of the Bragg interference-based reflection band across the entire visible spectrum. By studying five different systems, a set of important principles for manufacturing photonic colloids is established. Two swelling additives are required, one of which must exhibit strong interactions with one of the BCP blocks. The additives should be chosen to enhance the dielectric contrast, and the formation kinetics of the spheres must be sufficiently slow to enable the emergence of the photonic morphology. The proposed approach is versatile and robust and allows the scalable production of photonic pigments with possible future applications in inks for cosmetics and arts, coatings, and displays.

Tunable Bright White Light Emission with Ultra‐High Color Rendering Index Induced by Trigonal Bipyramid Unit

AbstractEfficient broadband emitting organic–inorganic metal hybrids (OIMHs) have attracted great attention recently as promising single‐component white light emitters. Here a new zero‐dimensional (0D) OIMH (C13H14N)2InCl5 (C13H14N+ = N‐methyldiphenylammonium) is reported, which features unique five‐coordinated [InCl5]2− trigonal bipyramid motif. For the first time, it is demonstrated that the trigonal bipyramid units in 0D OIMH can act as luminescence centers, showing blue emission under UV light. Remarkably, incorporating Sb3+ in [InCl5]2− trigonal bipyramids induces a new dual‐band emission at 540 and 735 nm resulting from the singlet and triplet self‐trapped excitons in [SbCl5]2−, leading to complete coverage of the entire visible spectrum. The resulting emissions in (C13H14N)2InCl5:Sb3+ are tunable from cold to warm white with the correlated color temperatures changing from 5574 to 3473 K and more importantly, an ultra‐high color rendering index (CRI) up to 96 being observed, which is comparable to the highest value in hybrid metal halides. A high photoluminescence quantum yield of 46.26% is simultaneously obtained in this system. This work demonstrates that the 0D OIMH with trigonal bipyramid motif is an excellent system for realizing the single‐component white light emission with both high efficiency and ultra‐high CRI.

Interface layer modulation of an all-inorganic perovskite solar cell to study the carrier transport mechanism

Over the past decade, organic halide perovskite has been an excellent absorber in solar cells. However, their stability issues have forced the research community to search for purely inorganic perovskites. In this work, we designed a perovskite solar cell based on a purely inorganic Cs0.8Rb0.2SnI3 absorber layer with inorganic carrier transport layers using SCAPS-1D simulation software. Using this exemplary architecture, we have discussed different carrier movement mechanisms in the conduction and valence bands through the interfaces of the absorber and carrier transport layers by instigating two interface layers. Our results illustrate the variation in device performance with the electron affinities and diffusion lengths. In addition, the study demonstrates a positive impact of Rb doping in CsSnI3 based perovskite solar cells. The absorber thickness and defect density optimization are also executed to maximize the solar cell performance. The optimized electron affinities of the interface layers are found to be 4.1 and 4.3 eV, respectively. The final model of the device has achieved a photo-conversion efficiency of 23% with a short circuit current of about 30 mA cm−2. The optimized model covers the entire visible solar spectrum with a quantum efficiency of >90%.

Facile Synthesis of Highly Emissive All-Inorganic Manganese Bromide Compounds with Perovskite-Related Structures for White LEDs

Lead-free all-inorganic halide materials with different Mn2+-based crystal structures (Cs3MnBr5 and CsMnBr3) were obtained using a convenient synthetic method. Cs3MnBr5 had a bright green emission (522 nm), with a unique single-exponential lifetime (τavg = 236 µs) and a high photoluminescence quantum yield (82 ± 5%). A red emission was observed in the case of the CsMnBr3 structure with a two-exponential fluorescence decay curve, and the lifetime was 1.418 µs (93%) and 18.328 µs (7%), respectively. By a judicious tuning of the synthetic conditions, a mixed phase of Cs3MnBr5/CsMnBr3 was also produced that emitted white light, covering almost the entire visible spectrum. White-light-emitting diodes (WLEDs) with color coordinates (0.4269, 0.4955), a color temperature of (3773 K), and a color rendering index (68) were then fabricated using the as-prepared powder of mixed phases of Cs3MnBr5/CsMnBr3 with a commercial UV LED chip (365 nm).

Preparation of triangular silver nanoplates by improved light-driven seed growth method

Triangular silver nanoplates have been synthesized by the improved light-driven seed growth method with only trisodium citrate as both photoreducing reagent and capping reagent under the irradiation of sodium lamp. • Triangular silver nanoplates (TSNPs) can exhibit tunable plasmonic properties across the entire visible spectrum and in the near-infrared region. • TSNPs have been synthesized by the improved light-driven seed growth method with only trisodium citrate as both photoreducing reagent and capping reagent. • The simple rapid preparation process will make it apply in large scale. Triangular silver nanoplates (TSNPs) have attracted much attention for their tunable plasmonic properties. In this letter, TSNPs have been synthesized by the improved light-driven seed growth method with only trisodium citrate (TSC) as both photoreducing reagent and capping reagent. By means of this high efficient method, TSNPs could be produced in high yield. As a kind of promising material, TSNPs will be used for chemical and biological sensing, and they can also be applied in optical limiters against high intensity laser pulse.

Barrierless Exciton Self‐Trapping and Emission Mechanism in Low‐Dimensional Copper Halides

AbstractLow‐dimensional copper halides having nontoxic elements are attracting increasing attention for their peculiar emission properties. Self‐trapped excitons (STEs) account for their high photoluminescence quantum yields (PLQYs) with emission that can stretch across the entire visible spectrum. However, intrinsic factors that influence the formation or loss of the emissive species in low‐dimensional copper halides remain elusive. Here, a comprehensive study on the STE formation dynamics of one‐dimensional CsCu2I3 and zero‐dimensional Cs3Cu2I5 is presented. It is found from STE kinetic analysis that a slower STE formation demonstrated by the 1D structure is not hindered by a potential barrier, but instead related to the number of phonons released in the self‐trapping process. It is further revealed that in 1D CsCu2I3, the non‐radiative recombination of STEs mainly occurs via the intersection between the STE state and the ground state in the configuration coordinate diagram, placing an intrinsic limit on the PLQY at room temperature. These findings show that the STE formation is affected by both the self‐trapping depth and the phonon energy as opposed to a potential barrier in low‐dimensional copper halides. The better understanding of STE formation and recombination processes provide basis for improving design and performance for broadband light emitting devices.

Mechanically stable ultrathin flexible metallic Au/Pt/Au tri-layer as an alternative transparent conducting electrode for optoelectronic device applications

Indium tin oxide (ITO) is a ubiquitous transparent conducting oxide employed in several modern optoelectronic devices. However, due to limited availability and fast depletion of indium, there is an urge to supplement its use with suitable alternatives in appropriate sheet resistance range, depending on the application requirement. In this scenario, an alternative flexible transparent conducting Au/Pt/Au ultrathin metallic tri-layer electrode sputter-deposited on PET substrate is explored. The tri-layer shows maximum transmittance of 55% at 500 nm and it presents a nearly flat behavior in the entire visible spectrum. Electrical transport properties of Au/Pt/Au layer show sheet resistance of 66 Ω/□ and mobility of 8.32 cm2V−1s−1, respectively. The contact angle measurement indicates that plain hydrophilic PET (62.6°) turns hydrophobic (94.2°) upon coating with Au/Pt/Au tri-layer. The surface properties analyzed using atomic force microscopy and optical profilometry indicate a crack-free, densely packed homogenous film. The tri-layer film shows mechanical stability up to 50,000 bending and twisting cycles. The obtained surface work function of Au/Pt/Au tri-layer film is 4.97 eV. The ultrathin flexible Au/Pt/Au tri-layer explored as top electrode in a piezoelectric generator and as top and bottom electrodes in an alternating current driven electroluminescent device exhibits appreciable performance.

Changes in electronic and optical characteristics of halogen–alkali adsorbed WSe2 monolayer

Adsorbing halogen and alkali metals atoms modify the optical and electrical characteristics of WSe2 monolayer (2D). The electrical and optical characteristics of the Wse2 monolayer, alkali and halogen atoms adsorbed WSe2 structures are investigated through density functional theory (DFT) simulations. The pristine WSe2 monolayer has insignificant absorption in the infrared and most parts of the visible region, and substantial absorption in the ultraviolet (UV) region (λ < 410 nm) as well as in a small section of the visible spectrum. The absorption coefficient of alkali–halogen adsorbed structures of WSe2 seems to expand with wavelength, and absorption peaks move toward the higher energy region of the optical spectrum, resulting in redshift effect. Significant absorption is observed in the entire visible spectrum (~ 410 to 780 nm) for both alkali and halogen adsorbed WSe2 nanostructures. The chlorine, bromine, and iodine adsorbed WSe2 structure shows larger absorption in the entire visible region among all other adsorbed structures. Presence of absorption peaks in the visible range of wavelengths rather than in the UV region, is beneficial for optoelectronic applications such as LEDs, CRTs, solar cells, and sensors. Trends in computed dielectric constant and refractive index values are also found to be compatible with trends in absorption coefficient values.

A Single‐Step‐Grown Semiconducting vdW Heterostructure of Tungsten Oxide–Sulfide for High‐Performance Photodetection

AbstractUltrathin semiconducting van der Waals (vdW) heterostructures based on transition metal dichalcogenides (TMDs) play a critical role in developing next‐generation electronic and optoelectronic devices. The replacement of one component of the heterostructure by transition metal oxides (TMOs) certainly brings in numerous benefits including long‐term stability and novel functionalities. However, the single‐step chemical‐vapor deposition growth of TMOs/TMDs vdW heterostructures, as a highly desired approach for large‐scale fabrication and practical implementation, is challenging due to contradictory growth atmospheres of TMOs and TMDs. Here, the single‐step growth of an ultrathin WO3–x/WS2 vdW heterostructure based on the quantity‐driven discrepant interaction between S and the precursor, in which S induces sulfidation to produce WS2 in the S‐rich phase and is changed to the reduction role to obtain sub‐stoichiometric WO3–x in the S‐deficient phase is realized. Both WO3–x and WS2 exhibit semiconducting properties with a favorable type‐II band alignment. A wide response across the entire visible spectrum with a large photo‐responsivity of 4375 A W−1, a detectivity of 5.47 × 1011 Jones, and sub‐ms switching kinetics at 405 nm is achieved without gating bias, which is significantly improved over other reported ultrathin vdW heterostructures. This study demonstrates the possibility of single‐step‐growing TMOs/TMDs vdW heterostructures and their strong potential in high‐performance optoelectronic devices.

Optically imprinted polarization gratings with a twisted nematic liquid crystal as a photomask

Liquid crystal Pancharatnam–Berry phase optical elements (LCPBOEs) are becoming increasingly attractive elements to be used to enhance near-eye displays or manipulate light beams, owing to their flatness and circular polarization-dependent behavior. The optical imprinting technique that is one of the commonly used methods for fabricating LCPBOEs is considered to be the most promising technique for mass production at a low cost, but the design of the photomask must be improved. In this work, a photomask that is based on a twisted nematic liquid crystal polarization grating (TNLCPG) cell, acting as a broadband linear polarization rotator, is designed. This TNLCPG cell, with a predefined alignment profile of a polarization grating, can convert linearly polarized light into a light field with spatially varying linear polarization and exhibits broadband operation over the entire visible spectrum. The designed TNLCPG photomask is used to demonstrate a liquid crystal polarization grating (LCPG) film using a white flashlight as a writing source. A high diffraction efficiency of greater than 95% is obtained. With its simple design and fabrication, the proposed TNLC-based photomask can potentially be used in the fabrication of LCPBOEs.

Effect of Ethylene Glycol: Citric Acid Molar Ratio and pH on the Morphology, Vibrational, Optical and Electronic Properties of TiO2 and CuO Powders Synthesized by Pechini Method.

High-purity TiO2 and CuO powders were synthesized by the Pechini method, an inexpensive and easy-to-implement procedure to synthetize metal oxides. The variables of synthesis were the ethylene glycol:citric acid molar ratio and the pH. High reproducibility of the anatase and tenorite phase was obtained for all synthesis routes. The degree of purity of the powders was confirmed by XRD, FTIR, UV-Vis absorption and XPS spectra. SEM and TEM images revealed the powders are composed of micrometer grains that can have a spherical shape (only in the TiO2) or formed by a non-compacted nanocrystalline conglomerate. FTIR spectra only displayed vibrational modes associating TiO2 and CuO with nanoparticle behavior. UV-Vis absorption spectra revealed the values of maximum absorbance percentage of both systems are reached in the ultraviolet region, with percentages above 83% throughout the entire visible light spectrum for the CuO system, a relevant result for solar cell applications. Finally, XPS experiments allow the observation of the valence bands and the calculation of the energy bands of all oxides.

Volatile Organic Compound Sensing Array and Optoelectronic Filter System using Ion-Pairing Dyes with a Wide Visible Spectrum.

An ideal dye-based sensing array has essential design requirements, including facile preparation methodology, tolerance to water vapor, a broad range of color-responsive changes, and a simple readout system. Here, a brief synthetic route is developed for ion-pairing dyes exhibiting unusual chromatic changes across the entire visible spectrum. It requires only mixing and precipitation under mild conditions. The dyes are applied to a sensing array containing 12 sensing elements with different initial states. Owing to the numerous color variations of the dyes, the color map generated by the array is highly simple yet sufficiently accurate to distinguish among the different functional groups (such as amines, aldehydes, and carboxylic acids) as well as carbon chain lengths. Principle component analysis (PCA) demonstrates that volatile organic compounds (VOCs) can be well classified according to the color changes of the sensing array. The ion-pairing dyes are embedded into3Dstacked nanofibers via electrospinning, and function as effective harmful-gas (e.g., formaldehyde) sensors with sub-ppm theoretical detection limits (0.15ppm). Finally, the 3D stacked nanofibers can be employed in an optoelectronic filter system that automatically checks for formaldehyde in the surroundings and also confirms the effective removal of the detected formaldehyde by the gas filter cartridge.

Omnidirectional, thin metasurface exhibiting selective absorption for un-polarized broadband incidence.

Thin devices with large areas have strong and omnidirectional absorption over a wide bandwidth and are in demand for applications such as energy harvesting, structural color, and vehicle LiDAR (laser detection and ranging). Despite persistent efforts in the design and fabrication of such devices, the simultaneous realization of all these desired properties remains a challenge. In this study, a 190-nm-thick metasurface with an area of 3 cm2, incorporating dielectric cylinder arrays, a chromium layer, a silicon nitride (SiNx) layer, and an aluminum layer is theoretically and experimentally demonstrated. The developed device achieves an average absorptivity of ∼99% (97% in the experiment) in the entire visible spectrum 400-700 nm. Moreover, it exhibits strong absorption over a wide range of incident angles (∼91% and 90% at 60° in the calculation and experiment, respectively). Importantly, the feasibility of applying the developed metasurface absorber to solar thermophotovoltaics and vehicle LiDAR (laser detection and ranging) has been explored. Moreover, the photoresist can be replaced by other glues and easily scaled up to a large area using the roll-to-roll nanoimprinting process. With the excellent spectral properties and performance, this device is promising for large-area applications.

A nano-liter droplet-based microfluidic reactor serves as continuous large-scale production of inorganic perovskite nanocrystals

Lead halide perovskite nanocrystals (NCs) exhibit high photoluminescence quantum yield (PLQY), high defect tolerance, narrow half peak width, and wide luminous gamut, making them the ideal optoelectronic materials in numerous fields. Nonetheless, their production still suffers from the limited productivity at the bench level. In this work, we fabricated CsPbX3 (X = Cl, Br, I) NCs within droplet-based micro-reactors, where both the nucleation and growth processes could be precisely controlled inside 130-nL microdroplets. This provides a new paradigm for the large-scale synthesis of perovskite NCs with high PLQY. Compared with other synthetic methods, this method can increase the concentration of reactant precursors by 3–116 times, while lowering the ligand to reactant ratio to 2%–50% of the commonly used hot-injection method. By modulating the reaction temperature and residence time, the structure-function relationship between the morphology of NCs and PL properties was extensively investigated. The microfluidic-based process allows the flexible adjustment in the proportion of PbX2 precursors to achieve the fabrication of perovskite NCs whose luminescence range covers the entire visible spectrum (406–677 nm) within one reaction. Finally, perovskite NCs with different halide ions were encapsulated in polymethyl methacrylate to prepare a colored light-emitting diode strip.