Entire Visible Light Research Articles

Semi‐Transparent, Micrometer Resolution p‐NiO/n‐ZnO Heterojunction Diode Temperature Sensors with Ultrathin Metal Anode

AbstractVarious temperature sensitive biological mechanisms have been utilized for new biomedical engineering tools such as neuromodulation, cancer cell hyperthermia or photothermal therapy. Optically transparent and high spatio‐temporal resolution temperature sensors are needed to precisely analyze the biological effects that occur in response to the temperature changes. In this work, semi‐transparent p‐NiO/n‐ZnO heterojunction diode‐based temperature sensors with 100 µm‐diameter ultrathin transparent Au/Ag metal anodes is introduced. The fabricated diode temperature sensors accurately measure temperature changes from 25 to 80 °C, which is of significant interest in many biomedical engineering applications. The sensors also exhibit adequate transparency over the entire visible light spectrum for biomedical imaging including fluorescent microscopy. Low‐power operation of the temperature sensor (<0.2 nW) is achieved to avoid a self‐heating effect. The micro‐scale spatial resolution of the transparent temperature sensors is especially useful for cellular resolution bio‐imaging, optical neural recording, and optical bio‐modulation where transparency and high‐resolution temperature sensing are necessary.

Ultrathin MoS2 nanosheet as co-catalyst coupling on graphitic g-C3N4 in suspension system for boosting photocatalytic activity under visible-light irradiation

In this study, ultrathin molybdenum disulfide (MoS2) nanosheets with thickness of 1.6–8.8 nm were obtained by liquid-phase exfoliating bulk MoS2. Then, they were employed as cocatalyst to build ultrathin MoS2/g-C3N4 heterojunction by self-assembly method. The degradation reaction of chlorimuron-methyl herbicide and tetracycline antibiotics under visible light was used to evaluate the photocatalytic properties of ultrathin MoS2/g-C3N4. The results showed that ultrathin MoS2/g-C3N4 composite exhibit superior photocatalytic performance. The MoS2/g-C3N4 composite with 15 wt% of ultrathin MoS2 nanosheet exhibited the highest degradation efficiency with 90.4% for chlorimuron-ethyl and 91.7% for tetracycline in 45 min under simulated sunlight, which was 8.8 times and 13.4 times than that of bare g-C3N4, respectively. The outstanding photocatalytic activity of ultrathin MoS2/g-C3N4 heterojunction thanks to the unique features of ultrathin MoS2 nanosheet that it harvesting the entire visible light, increasing the contact surface area with the support and shortened the electron and ion migration length, as well as more exposed edge sulfur atoms as redox centers. The radical scavenger experiments showed that •OH and •O2- plays a key role in the photocatalytic degradation process. This study provides a new idea for the design of high-activity a co-catalyst, that is, ultrathin MoS2 nanosheet has a significant influence on the photocatalytic performance of MoS2/g-C3N4 heterostructure photocatalyst.

Two-dimensional g-C3N4/Ti2CO2 heterostructure as a direct Z-scheme photocatalyst for water splitting: A hybrid density functional theory investigation

By using first-principles calculations based on hybrid density functional theory, we investigate the electronic structures and photocatalytic properties of two-dimensional (2D) g-C 3 N 4 /Ti 2 CO 2 van der Waals (vdW) heterostructure. Results show that g-C 3 N 4 /Ti 2 CO 2 heterostructure has a staggered type-II band alignment, and a built-in electric field is formed at the interface due to significant charge transfer from g-C 3 N 4 to Ti 2 CO 2 . Interestingly, we observed spatially distinguished conduction band and valence band edges, and a direct Z-scheme photocatalytic mechanism can be established in the heterojunction, favorable for suppressed charge carrier recombination. We further demonstrate high catalytic activity of g-C 3 N 4 /Ti 2 CO 2 towards both hydrogen evolution and water oxidation reactions, and the heterojunction exhibits excellent light-harvesting capability with entire visible light absorption. These results not only provide fundamental insight into the photocatalyst with Z-scheme mechanism, but also shed light on future design and fabrication of 2D vdW heterojunctions as high-performance catalysts for technologically important chemical reactions. • Electronic properties of 2D g-C 3 N 4 /TiCO 2 vdW heterostructure are investigated by hybrid functional calculations. • It exhibits spatially distinguished conduction/valence band edges, and a built-in electric field is formed. • As a direct Z-scheme photocatalyt, g-C 3 N 4 /TiCO 2 has high catalytic activity towards hydrogen and oxygen evolution. • It demonstrates strong optical adsorption in the entire visible light region.

Realization of III-Nitride c-Plane microLEDs Emitting from 470 to 645 nm on Semi-Relaxed Substrates Enabled by V-Defect-Free Base Layers

We examine full InGaN-based microLEDs on c-plane semi-relaxed InGaN substrates grown by metal organic chemical vapor deposition (MOCVD) that operate across a wide range of emission wavelengths covering nearly the entire visible spectrum. By employing a periodic InGaN base layer structure with high temperature (HT) GaN interlayers on these semi-relaxed substrates, we demonstrate robust μLED devices. A broad range of emission wavelengths ranging from cyan to deep red are realized, leveraging the indium incorporation benefit of the relaxed InGaN substrate with an enlarged lattice parameter. Since a broad range of emission wavelengths can be realized, this base layer scheme allows the tailoring of the emission wavelength to a particular application, including the possibility for nitride LEDs to emit over the entire visible light spectrum. The range of emission possibilities from blue to red makes the relaxed substrate and periodic base layer scheme an attractive platform to unify the visible emission spectra under one singular material system using III-Nitride MOCVD.

Structural, electronic, and optic properties of Se nanotubes

A new category of tubular nanostructures solely composed of selenium was explored by using the density functional theory. Similar to those in carbon nanotubes, the armchair and zigzag tube-like structures formed as a roll-up α-Se nanoribbon. The zigzag (n ≤ 16, 0) nanotubes exhibit decreasingly narrow direct band gap, and the armchair (n, n) possess decreasingly moderate indirect gap. The strain energy of nanotubes is inversely proportional to the second power of the nanotube diameter. With increasing tube diameter, an initial rise and consequent decrease occurred in the effective masses to the limit value of α-Se monolayer. The carrier mobility of nanotubes is comparable with that of its monolayer with orders of 103 and 102 cm2V−1s−1 for electron and hole, respectively. The optical absorption spectra of α-Se nanotubes exhibit high absorbance in energy window cover the entire visible light spectrum. Therefore, α-Se nanotubes hold great potential for future applications in high-performance optoelectronics.

Perspective on single-emissive-layer white-LED based on perovskites

Perovskite emitters have attracted great attention in recent years owing to their excellent photoelectric performance with low-cost potential. Some very recent studies have revealed that perovskites not only have narrow emitting peak with high purity but also have multi-color or broad spectrum in entire visible light, even some single emissive layer-based white perovskite light-emitting diodes (SEL-WPeLEDs) have been confirmed, showing promise in lighting and display. In this Perspective, we summarized the issues and challenges faced by these perovskite-based SEL-WLEDs and proposed some feasible suggestions in improving their light-emitting performance, hoping to promote their applications in lighting and other optoelectronic devices.

Manipulating the electronic and photocatalytic properties of anatase TiO2 by metalloid doping

Improving the photocatalytic efficiency of photocatalysts is one of the most challenging and meaningful research topics. In this work, using first principles study, the crystal structure, formation energy, electronic structures and photocatalytic properties of metalloid doped TiO2 were investigated. The results show that Si and Te doped TiO2 have excellent photocatalytic activity in the entire visible light spectrum. This is because they have high visible light absorption efficiency, low photogenerated carrier recombination rate and more catalytic active sites. This work provides essential guidance for developing TiO2-based visible light photocatalysis.

Second Harmonic Generation Covering the Entire Visible Range from a 2D Material–Plasmon Hybrid Metasurface

AbstractOn‐chip coherent light source has always been fascinating and intriguing due to its various potential applications. In the past decades, there has been some progress in the development of chip coherent light (e.g., nanolaser, Bose‐Einstein condensation and nonlinear optical effects). However, these methods strictly depend on materials and extreme experimental conditions, and are usually not tunable. Here, a hybrid structure is designed which combines a chirped surface plasmon metasurface with a monolayer transition metal dichalcogenide (TMDC) to achieve a coherent second harmonic generation (SHG) covering the entire visible light spectrum. Using only finite number of metallic grooves, a continuous resonance tuning is obtained. By translating the metasurface in space, a space‐frequency locking SHG is demonstrated. Although the Q factor of the surface plasmon cavity is low, its near‐field enhancements of both fundamental and SH waves are still obvious. Significantly, the broad linewidth of plasmonic cavity leads to a large degree of overlap between adjacent localized modes, that enables the tuning of the output wavelength continuously at room temperature. Meanwhile, the exciton resonance also plays an important role. This monolithic tunable device demonstrates the potentials of 2D material‐plasmon hybrid metasurface and to construct an efficient broadband tunable on‐chip coherent light source.

Facile Fabrication of Trimodal Switchable Mirror Device with Zero Transmittance in the Black State

AbstractThe electrochromic mirror device (ECD) demonstrating transparent, mirror, and black states with zero transmittance in the black state is fabricated using facile dry deposition method. The device is capable of achieving both a highly reflective mirror and a complete black state. ECD is fabricated using a WO3 film deposited by nanoparticle deposition system (NPDS) and optical characteristics of its transparent, mirror, and black states are evaluated. Notably, the device demonstrates the mirror state with high reflectance over 80% and a black state that completely blocks the entire visible light, resulting in nearly zero transmittance. Device durability is evaluated over 100 cycles; the transmittance of the black and transparent states is measured to be 9.61%, 79.6% at its wavelength of 680 nm, respectively. Moreover, the reflectance of the mirror state at the same wavelength is measured to be 73.1% and 72.7% for the first and 100th cycles, respectively. Microstructural observations suggest that the visible light‐blocking effect is a consequence of the rough surface obtained using NPDS, which leads to uneven electrodeposition of Ag ions to produce localized surface plasmon resonance. Dry deposition method of the electrochromic layer is an excellent method for fabricating high‐contrast three‐mode electrochromic mirrors.

One-Dimensional Face-Shared Perovskites with Broad-Band Bluish White-Light Emissions.

In recent years, two-dimensional (2D) hybrid lead halide perovskites based on corner-shared [PbX6] octahedrons have received extensive attention with important potentials in single-component white-light emitting diodes (WLEDs) due to the soft and distorted crystal lattices. However, limited research focused on the one-dimensional (1D) perovskites although they possess similar structural superiorities to achieve this performance. Herein, by using different types of organic amine cations as structural direction reagents, we report one new type of hybrid 1D perovskites of APbCl3 (A = (DTHPE)0.5, DMTHP, DBN) based on the same 1D face-shared octahedral [PbCl3]- chains. Upon UV light excitation, these 1D APbCl3 perovskites exhibit intrinsic broad-band bluish white-light emissions covering entire visible light spectra with the highest photoluminescence quantum yield (PLQY) of 6.99%, which catches up with the values of previously reported 2D perovskites. Through the systematical studies of time-resolved, temperature-dependent PL emissions, theoretical calculations, and so on, these broad-band light emissions can be ascribed to the radiative transition within conjugated organic cations. The facile assembly process, intrinsic broad-band light emissions, and high PLQYs enable these 1D APbCl3 perovskites as new types of promising candidates in fabricating single-component WLEDs.

Zero-Dimensional Hybrid Cd-Based Perovskites with Broadband Bluish White-Light Emissions.

Recently, low-dimensional organic-inorganic hybrid metal halide perovskites acting as single-component white-light emitting materials have attracted extensive attention, but most studies concentrate on hybrid lead perovskites. Herein, we present two isomorphic zero-dimensional (0D) hybrid cadmium perovskites, (HMEDA)CdX4 (HMEDA=hexamethylenediamine, X=Cl (1), Br (2)), which contain isolated [CdX4 ]2- anions separated by [HMEDA]2+ cations. Under UV light excitation, both compounds display broadband bluish white-light emission (515 nm for 1 and 445 nm for 2) covering the entire visible light spectrum with sufficient photophysical stabilities. Remarkably, compound 2 shows a high color rendering index (CRI) of 83 enabling it as a promising candidate for single-component WLED applications. Based on the temperature-dependent, powder-dependent and time-resolved PL measurements as well as other detailed studies, the broadband light emissions are attributed to self-trapped excitons stemming from the strong electron-phonon coupling.

Tailorable Indirect to Direct Band-Gap Double Perovskites with Bright White-Light Emission: Decoding Chemical Structure Using Solid-State NMR.

Efficient white-light-emitting single-material sources are ideal for sustainable lighting applications. Though layered hybrid lead-halide perovskite materials have demonstrated attractive broad-band white-light emission properties, they pose a serious long-term environmental and health risk as they contain lead (Pb2+) and are readily soluble in water. Recently, lead-free halide double perovskite (HDP) materials with a generic formula A(I)2B'(III)B″(I)X6 (where A and B are cations and X is a halide ion) have demonstrated white-light emission with improved photoluminescence quantum yields (PLQYs). Here, we present a series of Bi3+/In3+ mixed-cationic Cs2Bi1-xInxAgCl6 HDP solid solutions that span the indirect to direct band-gap modification which exhibit tailorable optical properties. Density functional theory (DFT) calculations indicate an indirect-direct band-gap crossover composition when x > 0.50. These HDP materials emit over the entire visible light spectrum, centered at 600 ± 30 nm with full-width at half maxima of ca. 200 nm upon ultraviolet light excitation and a maximum PLQY of 34 ± 4% for Cs2Bi0.085In0.915AgCl6. Short-range structural insight for these materials is crucial to unravel the unique atomic-level structural properties which are difficult to distinguish by diffraction-based techniques. Hence, we demonstrate the advantage of using solid-state nuclear magnetic resonance (NMR) spectroscopy to deconvolute the local structural environments of these mixed-cationic HDPs. Using ultrahigh-field (21.14 T) NMR spectroscopy of quadrupolar nuclei (115In, 133Cs, and 209Bi), we show that there is a high degree of atomic-level B'(III)/B″(I) site ordering (i.e., no evidence of antisite defects). Furthermore, a combination of XRD, NMR, and DFT calculations was used to unravel the complete atomic-level random Bi3+/In3+ cationic mixing in Cs2Bi1-xInxAgCl6 HDPs. Briefly, this work provides an advance in understanding the photophysical properties that correlate long- to short-range structural elucidation of these newly developed solid-state white-light emitting HDP materials.

Control of Shielding Effectiveness of Optically Transparent Films by Modification of the Edge Termination Geometry

This article deals with the design, fabrication, and characterization of optically transparent electromagnetic screens to protect optical sensors against high-intensity radiated fields. To ensure the best tradeoff between high optical transparency over the entire visible light spectrum and high shielding effectiveness at microwaves, micrometric mesh metal films printed on glass substrates were selected. Changing the micrometric mesh pattern allows reaching various shielding effectiveness values required for different applications, but implies important adjustments of the design and fabrication processes. The variation of the number of contact ribbons between the mesh screen and its direct peripheral area consists of an alternative solution to modify the screen shielding effectiveness, while keeping the meshed part of the screen identical. An analytical model, which predicts the shielding effectiveness variation measured under statistically uniform illumination in a reverberation chamber as a function of the number of metal ribbons and the aperture sizes between them was specifically developed. Experimental results follow the trend predicted by the analytical model. As a result, adjusting the number of peripheral contact ribbons enables the shielding effectiveness to be fitted to specified requirements at constant optical transparency.

Electrochemically switchable electrochemiluminescent sensor constructed based on inorganic perovskite quantum dots synthesized with microwave irradiation

Microwave irradiation was employed to synthesize inorganic perovskite quantum dots (IPQDs) which were demonstrated to be monoclinic phase and behaved tunable photoluminescent emissions across the entire visible light spectrum. The microwave-based synthetic method was proved to be easy-operation, high-throughput and low-cost. These microwave-synthesized IPQDs exhibited electrochemically switchable electrochemiluminescence (ECL). Obvious ECL was obtained when holes were injected into the electron-injected IPQDs while almost no ECL was observed in the reverse process. ECL of IPQDs gave promise for constructing electrochemiluminescent sensors for hydrogen peroxide (H2O2) and dopamine (DA) detection. Linear relationships between ECL intensities and H2O2/DA concentrations were detected and satisfactory correlation coefficients were obtained. Our results shed the light on the ECL sensing application of the high-throughput microwave-synthesized IPQDs.

Dermo-optical perception of the visible range different wavelengths electromagnetic radiation by the palms skin of visually

Background. There is no single point of view which would explain the exact mechanisms of dermo-optical perception and nonspecific stimuli brain processing features at the moment, but to understand this perception peculiarities it is important to study the different skin receptors response to different colors. Objectives. The work aim is to determine the visible range different wavelengths electromagnetic radiation influence on the palms skin different types somatosensory receptors activity and nerve fibers involved in the skin innervation. Materials and methods. The experiments involved 12 visually impaired children (at their request and with their parents permission). The various somatosensory receptors condition measurement located on the palms, as well as the skin innervation of visually impaired children who participated in the dermo-optical perception training, was performed using the device "KSD" by recording and computer analysis of the electromagnetic oscillations emitted by the organism. Results. An experimental study of changes in the various somatosensory receptors activity located on the palms, as well as the visually impaired children skin innervation under the visible range different wavelengths electromagnetic radiation action was performed. It was found that under the light action, depending on the specific wavelengths, the studied receptors and nerve fibers are activated or suppressed. An increase in the thermal sensitivity activity (Ruffini's body) under the electromagnetic radiation influence on the palms skin in the wave range from 380-700 nm (in the entire visible light spectral range). The greatest activation was observed in «warm» (red, orange) and green colors. On white, black and «cold» colors (blue, blue) the Ruffini's bodies activation was less than on «warm» colors. Conclusions. The obtained experimental results indicate the palms skin various somatosensory receptors ability to adapt to the some information perception with a non-specific stimulus - the visible range electromagnetic radiation. It was found that the palms skin dermo-optical perception is due not only to temperature sensitivity (provided by thermoreceptors), but also to other types of receptors: baroreceptors (Pacinian corpuscles), tactile receptors (Meissner's corpuscles), mechanoreceptors (Golgi receptors).

Direct fabrication of Cd–In–S alloy quantum dots thin films

In this article, a new simple one-step process to fabricate Cd–In–S luminescent quantum dot thin films (QDTFs) is provided. Metal sulfide precursor solutions were manufactured by directly adding a certain amount of butylamine and carbon disulfide in the ethanol solution followed by dissolving Cd(OH)2 and In(OH)3 powder. Cd–In–S luminescent QDTFs can be obtained by mixing Cd and In precursor solutions and then spinning on a cover slip and annealing on a hot plate at 190 °C under air atmosphere directly without complicated synthesis method. By changing the sintering parameters including the temperature, time and ratios of (Cd+In)/ligand, the Cd–In–S luminescent QDTFs covering the entire visible light wavelength from 470 to 628 nm can be obtained. The Cd–In–S luminescent QDTFs exhibited remarkable optical properties and has potential application in solar cell and light emitting diode, with the photoluminescence quantum yield of up to 36.5%.

Converting an Organic Light-Emitting Diode from Blue to White with Bragg Modes

Organic light-emitting diodes (OLEDs) have been established as versatile light sources that allow for easy integration in large-area surfaces and flexible substrates. In addition, the low fabrication cost of OLEDs renders them particularly attractive as general lighting sources. Current methods for the fabrication of white-light OLEDs rely on the combination of multiple organic emitters and/or the incorporation of multiple cavity modes in a thick active medium. These architectures introduce formidable challenges in both device design and performance improvements, namely, the decrease of efficiency with increasing brightness (efficiency roll-off) and short operational lifetime. Here we demonstrate, for the first time, white-light generation in an OLED consisting of a sub-100 nm thick blue single-emissive layer coupled to the photonic Bragg modes of a dielectric distributed Bragg reflector (DBR). We show that the Bragg modes, although primarily located inside the DBR stack, can significantly overlap with the emissive layer, thus efficiently enhancing emission and outcoupling of photons at selected wavelengths across the entire visible light spectrum. Moreover, we show that color temperature can be tuned by the DBR parameters, offering great versatility in the optimization of white-light emission spectra.

Numerical Study of an Efficient Broadband Metamaterial Absorber in Visible Light Region

We report a numerical study of a broadband metamaterial absorber in visible light region by utilizing a single layer of metal–dielectric–metal configuration. The absorption bandwidth and absorption performances are tailored by varying the resonator shapes and metal materials. The absorption bandwidth of the proposed metamaterial absorber (MA) structure is enhanced significantly with decreasing the order of rotational symmetry of the resonator shape. Using gold configuration, the twofold symmetry MA structure based on the double-sized axe shaped resonator exhibits the broadband absorption response over the entire visible light and apart of infrared spectrum range from 320 to 982 nm with absorptivity above 90% for both transverse electric and transverse magnetic polarizations. The physical mechanism of broadband absorption is explained by the current, electric, and magnetic distributions, significantly affected by the propagating surface and localized surface plasmon resonances. Furthermore, the high absorber performances of the twofold symmetry MA structure can be obtained over entire visible light region (400–700 nm) for both noble metal of gold and low-cost metal of nickel configurations, indicating the proposed absorber is a promising candidate for low-cost and large-scale fabricate device operated in visible light region.

Improvement of 60 GHz Transparent Patch Antenna Array Performance Through Specific Double-Sided Micrometric Mesh Metal Technology

This paper presents the performance of optically transparent 4 × 2 microstrip patch antenna arrays operating at 60 GHz and made from double-sided micrometric mesh metal layers. A high level of optical transparency (higher than 80%) over the entire visible light spectrum coupled with a sheet resistance lower than 0.5 ohm/sq of the mesh metal films are achieved. Microwave performance of the transparent antenna arrays has been performed from two different mesh ground plane patterns and compared with those of an opaque antenna array made of double-sided continuous metal films. A gain value equal to 13.6 dBi at 58.0 GHz has been recorded, against 15.6 dBi at 59.7 GHz for the opaque antenna array. The influence of the mesh structure and mesh parameters of the ground plane is investigated and discussed. INDEX TERMS Micrometric metal mesh, Microstrip antenna arrays, Millimeter wave antenna, Optically transparent antenna

Transmissive structural color filters using vertically coupled aluminum nanohole/nanodisk array with a triangular-lattice

We demonstrate a configuration to generate transmissive structural colors through triangular-lattice square nanohole arrays in aluminum (Al) film with Al nanodisks on the bottom of the nanoholes. By using a simple nanofabrication process, colors covering the entire visible light with different brightness and saturation are achieved by tuning both the period of arrays and the size of nanoholes. The optical behaviors of the structures are systematically investigated by both experimental and theoretical methods. The results indicate that the localized surface plasmon resonance of nanohole arrays plays the key role in the extraordinary transmission and meanwhile the coupling of disks and holes is also of importance for the enhanced transmission. With the wide color gamut, these kinds of vertically coupled Al nanohole/nanodisk arrays show the capabilities for high-resolution full-color printing. Compared to existing transmissive plasmonic color filters, the configuration in this work has the advantages of a simple fabrication process and using cheap aluminum materials.