Entire Visible Light Range Research Articles

Tunable Spectral Emission from 0D Rb3ZnBr5 Crystals for Single‐Component Multi‐Color LED Applications

AbstractThe development of efficient, stable, and cost‐effective luminescent materials is crucial for advancing lighting and display technologies. In this study, a series of tunable luminescent materials based on the novel 0D all‐inorganic perovskite (AIP) crystal Rb₃ZnBr₅ (RZB) is obtained. The emission of Sn2⁺ doped RZB spans the entire visible light range and extends into the near‐infrared (NIR) region, achieving a photoluminescence quantum yield (PLQY) of 75%. The distinct lifetimes combined with theoretical calculations, indicate that the broadband dual‐peak emissions at 496 and 636 nm originate from the singlet and triplet states of Sn2⁺, respectively, which is rarely observed in Sn2⁺‐doped perovskite crystals. The phosphor RZB:Sn2⁺ demonstrates the high thermal stability, along with excellent moisture and air stability. Co‐doping RZB with Sn2⁺ and Mn2⁺ broadens the excitation spectrum and allows precise control over the excitation wavelength, facilitating dynamic transitions from warm white to yellow and green light. This feature is particularly beneficial for multicolor LEDs and multi‐level anti‐counterfeiting applications.

Ultrabroadband invisibility cloaking design of a concentric multilayered cylindrical metamaterial

An ultrabroadband invisibility cloak is designed using a genetic algorithm (GA) for a cylindrical target with an infinite length. The cloaking band is 0.4 to 0.7µm, covering almost the entire visible light range. The invisibility cloaking medium consists of concentric multilayered cylindrical metamaterials (CM). When the cloaking target is covered with a well-designed 26+ layer CM, the average scattering cross-section is 6% or less of the uncloaked target’s cross-section. The cloaking performance of the structure designed by the GA was superior to that designed by analytical calculations based on a combination of the transformation optics and the effective medium approximation. The cloaking is confirmed through the time variation of the magnetic fields calculated using the finite-difference time-domain method. In addition, the mechanism of the cloaking is discussed.

Oxygen‐Tolerant Near‐Infrared Organic Long‐Persistent Luminescent Copolymers**

AbstractOrganic materials exhibiting long‐lasting emission in the near infrared are expected to have applications in bio‐imaging and other areas. Although room temperature phosphorescence and thermally activated delayed fluorescence display long‐lived emission of approximately one minute, organic long‐persistent luminescence (OLPL) systems with a similar emission mechanism to inorganic persistent emitters can emit for several hours at room temperature. In particular OLPL with a hole‐diffusion mechanism can function even in the presence of oxygen. However, ionic materials lack long‐term stability in neutral organic host owing to aggregation and phase separation. In this study, we synthesized polymers with stable near‐infrared persistent luminescence at room temperature via the copolymerization of electron donors and acceptors. The copolymers exhibit long‐persistent luminescence (LPL) at temperatures below the glass transition temperature and can be excited by approximately the entire range of visible light. LPL properties and spectra can be controlled by the dopant.

Oxygen-Tolerant Near-Infrared Organic Long-Persistent Luminescent Copolymers.

Organic materials exhibiting long-lasting emission in the near infrared are expected to have applications in bio-imaging and other areas. Although room temperature phosphorescence and thermally activated delayed fluorescence display long-lived emission of approximately one minute, organic long-persistent luminescence (OLPL) systems with a similar emission mechanism to inorganic persistent emitters can emit for several hours at room temperature. In particular OLPL with a hole-diffusion mechanism can function even in the presence of oxygen. However, ionic materials lack long-term stability in neutral organic host owing to aggregation and phase separation. In this study, we synthesized polymers with stable near-infrared persistent luminescence at room temperature via the copolymerization of electron donors and acceptors. The copolymers exhibit long-persistent luminescence (LPL) at temperatures below the glass transition temperature and can be excited by approximately the entire range of visible light. LPL properties and spectra can be controlled by the dopant.

Fabrication of Moth-Eye Structures with Precisely Controlled Shapes by Nanoimprinting Using Anodic Porous Alumina Molds

An anodic porous alumina mold with tapered pores, which can be used to form moth-eye structures, was formed by repetitions of anodization and etching. It was shown that the controllability of the pore shape of the anodic porous alumina mold improved with the number of repetitions of anodization and etching. However, it was found that even when the total anodization time or anodic charge (electrical current × time) was kept constant, the thickness of anodic films was not constant because the total etching time varied. This is because the etching of the anodic porous alumina mold not only increases the pore size but also reduces the thickness of the barrier layer so that pore growth proceeds after the barrier layer is re-formed during re-anodization. Therefore, it was found that if anodization is performed with the additional anodic charge required to re-form the barrier layer, an anodic porous alumina mold with tapered pores and uniform film thickness can be produced even if the etching time is varied. Nanoimprinting using the resulting anodic porous alumina mold was shown to form a moth-eye structure with a reflectance of less than 0.1% over the entire visible light range.

Effects of tensile strain on the electronic, optical and ferroelectric properties of a multifunctional R3c InFeO3 compound

The search for materials with appropriate ferroelectric and photovoltaic properties is an intense field of research. The main objective of these studies is to obtain efficient materials for solar cell applications. In this work, non-collinear spin density functional theory calculations are performed to describe the electronic, optical, and ferroelectric properties of a multiferroic R3c InFeO3 compound under tensile strain. Our studies reveal that under conditions of tensile strain, this material had ideal fundamental properties for photovoltaic applications. Under 9% tensile strain of the R3c InFeO3 unit cell volume (a = 5.536 Å and c = 13.808 Å), a direct energy band gap of 1.74 eV was found. With this energy band gap, the material absorbs the entire range of visible light, and for a film thickness of up to 100 nm it reaches a maximum photoconversion efficiency of 20%, a higher value than observed in some semiconductors that are used in practice. Furthermore, the effective mass of charge carriers (m*), and the exciton binding energy (Eb) are significantly decreased (m* < 0.4 m0 and Eb < 1.0 meV), which likely to lead to better charge mobility and easier separation of the electron-hole pair in the process of photoabsorption. Under this level of strain, the spontaneous electric polarization was reduced to 77.6 µC/cm2, a value that is still higher than other ferroelectric-photovoltaic materials.

Noble metal-free doped graphitic carbon nitride (g-C3N4) for efficient photodegradation of antibiotics: progress, limitations, and future directions.

Graphitic carbon nitride (g-C3N4) is well recognised as one of the most promising materials for photocatalytic activities such as environmental remediation via organic pollution elimination. New methods of nanoscale structure design introduce tunable electrical characteristics and broaden their use as visible light-induced photocatalysts. This paper summarises the most recent developments in the design ofg-C3N4 with element doping. Various methods of introducing metal and nonmetal elements into g-C3N4 have been investigated in order to simultaneously tune the material's textural and electronic properties to improve its response to the entire visible light range, facilitate charge separation, and extend charge carrier lifetime. The degradation of antibiotics is one of the application domains of such doped g-C3N4. We expect that this research will provide fresh insights into clear design methods for efficient photocatalysts that will solve environmental challenges in a sustainable manner. Finally, the problems and potential associated with g-C3N4-based nanomaterials are discussed. This review is expected to encourage the ongoing development of g-C3N4-based materials for greater efficiency in photocatalytic antibiotic degradation.

Recovery of gelatin from poultry waste: Characteristics of the gelatin and lotus starch-based coating material and its application in shelf-life enhancement of fresh cherry tomato

In recent years, food packaging has advanced from contaminating and polluting waste that remains after the use of the food product towards a functional ingredient that can be consumed along with the food product. Edible coatings are a healthy substitute for traditional food packaging. Therefore, the present study was aimed to develop edible coating material based on poultry waste gelatin and lotus stem starch for shelf-life extension of cherry tomatoes. The recovery of gelatin from chicken Feet (CF) and starch from lotus stem waste (LSW) was 14.5% and 9.20%, respectively and were used in different proportions for the development of the coating material. The flow behavior of coating material was pseudoplastic as the flow index (n) ranged from 0.332 to 0.428. The consistency coefficient (k) ranged from 1.62 to 4.92 Pa.sn, and it increased with the starch concentration. Storage modulus decreased with changing temperature from 10°C to 25°C and 10–35 °C in starch-free and starch-containing solutions, respectively. FTIR transmission band shifted from 3313 to 3343 cm−1 with changing the starch concentration from 0% to 10%, indicating the strong interactions of OH and amino groups. The transmission of UV light was low and remained unaffected, however, the transmittance showed a decrease with the starch concentration in the entire visible light range. The firmness and pH were retained to a greater extent and the weight loss in tomatoes was minimized during the 15 days of storage. The study revealed that this coating material may have great potential in the shelf-life extension of fresh fruits and vegetables.

Surfactant induced bilayer-micelle transition for emergence of functions in anisotropic hydrogel.

Tuning the self-assembled structures in amorphous hydrogels will enrich the functionality of hydrogels. In this study, we tuned the structure of a photonic hydrogel, which consists of polymeric lamellar bilayers entrapped inside a polyacrylamide network, simply by molecular triggering using an ionic surfactant. Owing to the binding of ionic surfactants (sodium dodecyl sulfate), the lamellar bilayers comprising non-ionic polymeric surfactants [poly(dodecyl glyceryl itaconate)] changed to micelles, whereas the unidirectional lamellar structure was preserved in the hydrogel. The bilayer-micelle structure transition caused a dramatic decrease in the swelling anisotropy and mechanical softening of the photonic gel. With the micelle structure, the softened gel shows fast (0.3 s) and reversible color change over the entire visible light range in response to a small mechanical pressure (5 kPa). This low stress-induced color-changing hydrogel could be applied as a visual tactile sensor in various fields, especially in biomedical engineering.

First principles study of photogalvanic effect of monolayer SnS

The photogalvanic effect of monolayer SnS was investigated at a small bias voltage under perpendicular irradiation using density functional theory combined with the non-equilibrium Green’s function method. The photocurrent was generated over the entire visible light range, and it was saturated at a small bias voltage for photon energies of 2.4, 2.6, 3.2 and 3.4 eV. The photocurrent shows cosine dependence of the polarization angle, which is attributed to the second-order response to the photoelectric field. These results provide a deeper understanding of the photogalvanic properties of the 2D SnS nanosheet based devices.

Thiophene-benzothiadiazole based donor–acceptor–donor (D-A-D) bolaamphiphiles, self-assembly and photophysical properties

ABSTRACT Bolaamphiphilies with D-A-D type π-conjugated rigid cores composed by thiophenes as donors (D) and benzothiadiazole (BTD) as central acceptor (A) have been synthesised. Their self-assemblies and photophysical properties were investigated by polarising optical microscope, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy. Such compounds can self-assemble into honeycomb cylinder mesophases with Colhex∆/p6mm and Colsqu/p4mm lattices in their pure states as well as organogels with different morphologies in organic solvents. Their absorption spectra cover nearly the entire visible light range and their band gaps are relatively low. Tetrathiophene BTD based bolaamphilphiles (BT4/n ) with higher D/A ratios than the bisthiophene BTD bolaamphilphiles (BT2/n ) can self-assemble into more ordered nanostructures in both bulk states and solution. Both the absorption and emission peaks of BT4/n are strongly red shifted. The influence of the molecular conformation, the conjugated core length, as well as the D/A ratio on the self-assemble and photophysical characteristics of such D-A-D bolaamphiphiles are discussed.

Doping of Graphitic Carbon Nitride with Non-Metal Elements and Its Applications in Photocatalysis

This review outlines the latest research into the design of graphitic carbon nitride (g-C3N4) with non-metal elements. The emphasis is put on modulation of composition and morphology of g-C3N4 doped with oxygen, sulfur, phosphor, nitrogen, carbon as well as nitrogen and carbon vacancies. Typically, the various methods of non-metal elements introducing in g-C3N4 have been explored to simultaneously tune the textural and electronic properties of g-C3N4 for improving its response to the entire visible light range, facilitating a charge separation, and prolonging a charge carrier lifetime. The application fields of such doped graphitic carbon nitride are summarized into three categories: CO2 reduction, H2-evolution, and organic contaminants degradation. This review shows some main directions and affords to design the g-C3N4 doping with non-metal elements for real photocatalytic applications.

Fabricating multilayer antireflective coating for near complete transmittance in broadband visible light spectrum

Abstract To extract maximum performance out of the certain optical devices it is highly desirable to use completely transparent window in a broad wavelength range. In search of large-scale applicable antireflective (AR) coating for such window, herein we report the design and fabrication of multilayer coating with the aim to reduce the reflection of the window in the entire visible light range. Systematic selection of material and thickness of each layer was performed based on the criteria fulfilled by refractive index to obtain zero reflection. Low refractive index material like MgF2 is deposited by e-beam technique to obtain single-layer AR coating. While Al2O3 and ZrO2, deposited by RF-magnetron sputtering, with MgF2 are used to develop multilayer AR coating. Scanning electron microscope image along with elemental line scan obtained along the cross-section of the coating verified the thickness and composition of each layer. Deposition of four-layer AR coating (MgF2/Al2O3/ZrO2/MgF2) on both side of quartz window with optimized thickness showed considerable reduction in the reflection to 0.6% at 550 nm. The average transmittance of 99.1% was recorded in the broadband of visible spectrum in the range of 450–750 nm wavelength. With near to complete transmission, the present AR coating holds encouraging prospect for implementing in windows of digital display, photovoltaic module, and other optoelectronic devices.

Preparation and properties of black Ti-doped zirconia ceramics

Black zirconia ceramics has many problems, such as uneven color and poor phase stability. The reason for this phenomenon is that the colorant uses a colorant with a complex black spinel structure, and also the application of a dyeing method. To improve the color uniformity and phase stability of black ceramics, TiO2 was introduced to replace the traditional complex black spinel, a high-temperature reduction method (HTR) was employed to prepare a black Ti-doped zirconia ceramic, stead of the conventional dyeing method. After the HTR at 1400 °C, the concentration of Ti3+ and oxygen vacancies increased, and the lightness of the ceramic samples decreased from 93.48 to 44.17. The black ceramic is uniform in color and stable in phase, avoiding the disordered phase of the spinel doped multiphase zirconia ceramic. The results indicate that the overall color of the samples depends on the development mechanism of the color center. The formation of color centers (F+ centers) in this work was related to the electronic transition of Ti 3d states and oxygen vacancies generated during the HTR. F+ centers cause a strong light absorbance over the entire visible light range (400–750 nm), so that the color of the ceramics is black. Based on their good color attributes, black ceramics have great potential in industry, for example as the back plate of mobile phones.

Fabrication of Cross-Sinusoidal Anti-Reflection Nanostructure on a Glass Substrate Using Imperfect Glass Imprinting with a Nano-Pin Array Vitreous Carbon Stamp.

Although polymer nanoimprinting on glass substrates has been widely employed for the fabrication of functional anti-reflective (AR) nanostructures, several drawbacks exist with respect to durability and delamination. The direct patterning of glass material is a potential solution for outdoor applications that require AR functional nanostructured glass plates. In this study, a glass imprinting technique was employed for the fabrication of an AR nanostructure on a soda-lime glass substrate using a vitreous carbon (VC) stamp. The VC stamp, which had a high aspect ratio nanopost array with a pitch of 325 nm, diameter of 110 nm, and height of ~220 nm, was fabricated by the carbonization of a replicated Furan precursor from an Si master. During the glass imprinting process using the nanopost array VC stamp, the softened glass material gradually protruded into the spaces between the nanopins owing to viscoelastic behavior, and one can achieve a cross-sinusoidal surface relief under specific imprinting condition, which can be used as an AR nanostructure with a gradually increasing refractive index. The effects of the processing temperature on the surface profile of the glass imprinted parts and the measured transmission spectra were analyzed, and a glass imprinting temperature of 700 °C and pressure of 1 MPa were found to be the optimum condition. The height of the fabricated cross-sinusoidal nanostructure was 80 nm, and the light transmission was increased by ~2% over the entire visible-light range. Furthermore, the measured transmission spectrum observed to be in good agreement with the simulation results.

Defect-induced diverse electronic, magnetic and optical properties in monolayer CaP3

Monolayer CaP3 (mCaP3), a semiconductor predicted theoretically with suitable band gap and high electron mobility, shows potential applications in nanoelectronics and optoelectronics. In this work, using first-principles calculations, diverse electronic, magnetic and optical properties of mCaP3 were explored by substituting P atoms by B, C, N, O and F or introducing P and Ca vacancy, respectively. The results show that B and C prefer to substitute P atoms (denoted by P1) bonding with four adjacent P atoms, while N, O and F tend to substitute P (denoted by P2) bonding with two P and two Ca atoms. These two types of systems, expressed by X(P1)-mCaP3 (XB and C) and X(P2)-mCaP3 (XN, O and F), are favorable in energy. The systems of B(P1)-mCaP3, N(P2)-mCaP3 and F(P2)-mCaP3 with four different doping concentrations are found to be spin-non-polarized semiconductors. Notably, in N(P2)-mCaP3 and F(P2)-mCaP3, the band-gap is monotonically tuned by changing doping concentrations. In contrast, in C(P1)-mCaP3 and O(P2)-mCaP3, the spin-polarized semiconducting characters are obtained at the two low doping concentrations, and the transition from semiconducting to metallic states appears at the highest doping concentrations. Besides the tunable band gaps obtained, good optical absorption features in entire visible-light range are kept in all doped systems as the pristine one. In particular, an additional absorption peak in low energy region is induced by Ca vacancy and P substitution by C. These diverse electronic, magnetic and optical properties obtained by selective doping in mCaP3 will expand its potentials in future applications.

Quinoxaline and Pyrido[x,y-b]pyrazine-Based Emitters: Tuning Normal Fluorescence to Thermally Activated Delayed Fluorescence and Emitting Color over the Entire Visible-Light Range.

Quinoxaline (Q), pyrido[2,3-b]pyrazine (PP) and pyrido[3,4-b]pyrazine (iPP) are used as electron acceptors (A) to design a series of D-π-A-type light-emitting materials with different donor (D) groups. By adjusting the molecular torsion angles through changing D from carbazole (Cz) to 10-dimethylacridine (DMAC) or 10H-phenoxazine (PXZ) for a fixed A, the luminescence is tuned from normal fluorescence to thermally activated delayed fluorescence (TADF). By gradually enhancing the intramolecular charge-transfer extent through combining different D and A, the emission color is continuously and regularly tuned from pure blue to orange-red. Organic light-emitting diodes (OLEDs) containing these compounds as doped emitters exhibit bright electroluminescence with emission colors covering the entire visible-light range. An external quantum efficiency (ηext ) of 1.2 % with excellent color coordinates of (0.16, 0.07) is obtained for the pure-blue OLED of Q-Cz. High ηext values of 12.9 (35.9) to 16.7 % (51.9 cd A-1 ) are realized in the green, yellow, and orange-red TADF OLEDs. All PP- and iPP-based TADF emitters exhibit superior efficiency stabilities to that of analogues of Q. This provides a practical strategy to tune the emission color of Q, PP, and iPP derivatives with the same molecular skeletons over the entire visible-light range.

Synthesis and Properties of New Dithienosilole Derivatives as Luminescent Materials.

Three new organosilicon compounds based on dithienosilole (DTSi) were synthesized in good yields. We report the optical and electrochemical properties of the resulting derivatives. We find that these compounds absorb the light in the ultraviolet and blue light range, and they exhibit luminescence in almost the entire range of visible light. After electropolymerization were significantly lowered, the values of the energy gap (even 1.51 eV for P2) and the ionization potential of the polymers were compared to monomers. Optoelectronic properties of the obtained compounds suggest that these derivatives of DTSi may be good candidates as the emissive layers in white organic light-emitting diodes (WOLEDs), which would reduce the amount of layers.

Stretchable electrochromic devices enabled via shape memory alloy composites (SMAC) for dynamic camouflage

Electrochromic device is a kind of device that can produce color change under the actuation of electric signal. It has attracted wide attention because of its dynamic color change properties, color diversity and convenience of driving signals. These properties highlight its potential application prospects in dynamic display, anti-counterfeiting treatment, biomedicine and other fields. In this study, stretchable photonic crystals are prepared by nano-imprint technology, soft actuators made by shape memory alloy composites (SMAC) were developed based on shape memory alloy (SMA). A stretchable electrochromic device is obtained by integrating the stretchable photonic crystal and SMAC. The electrochromic properties of the device is tested under different voltages. It is found that under the voltage of 1.0 V–1.5 V, it can achieve color changing in entire visible light range, and the total deformation required is less than 30%. The properties of stretchable electrochromic devices based on SMAC is comparative analyzed with that of other electrochromic devices or structures. The results show that the proposed stretchable electrochromic device has the characteristics of low driving voltage, good compliance, wide color changing range, short response time and large effective color changing area. Finally, the excellent soft dynamic display and camouflage functions of stretchable electrochromic devices are demonstrated in a special pattern, and the high impact resistance of the device is verified. The results indicates that the proposed structure is a promising stretchable electrochromic device, which may have great potential for applications of chameleon-like camouflage functional materials and devices.

Stretchable photonic crystals with periodic cylinder shaped air holes for improving mechanochromic performance

Photonic crystals are able to change the macroscopic color by regulating the center wavelength of band gap with altering the lattice constant of nano-structures. Herein, stretchable photonic crystals, with periodic cylinder shaped air holes non-close-packed in triangular lattice, are designed and fabricated for mechanochromism in entire visible light range. Numerical simulation has verified the excellent mechanochromic ability for the proposed nano-structure. Then the stretchable photonic crystals with this structure are successfully prepared by nano-imprinting technology on PDMS. Subsequently, the mechanochromic properties of the prepared materials are studied, and color change over the entire visible light range from red to blue is observed under a small strain of 29%. In addition, cyclic stretching tests up to 2000 times show that the materials are capable of maintaining shape recovery ability as well as mechanochromic ability. Finally, a stretchable visual strain sensor is prepared using the stretchable photonic crystal. This sensor can distinguish three strain ranges below 30% of strain rate by its color change that offers a visual observation of strain ranges. The stretchable visual strain sensors is more sensitive to small strain than resistance sensors, which may have great potential for applications of visual monitoring stretching strain.