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Tantalum nitride (Ta3N5) is a very promising photoanode material due to its narrow band gap (2.1 eV) and suitable band alignment for solar water splitting. However, it suffers from severe photocorrosion during water oxidation. In this work, it was found that surface passivation by AlOx and TiOx layers results in dramatically different PEC performance of Ta3N5 photoanode for water oxidation. The mechanism study indicates that the negative charges on AlOx can generate additional field to promote separation of photogenerated charges, while the positive charges on TiOx layer show the opposite effect. As a result, the Ta3N5 based photoanode modified with AlOx layer gives a high photocurrent of 12.5 mA cm−2 for 24 h at 1.23 V versus the reversible hydrogen electrode (RHE). Dynamic analysis implies that the hole extraction and transfer are significantly improved by the modification with the AlOx layer. This work reveals the importance of the charges on surface passivation layer in interface engineering of photoelectrodes.

CsPbCl3 nanocrystals are potential ultrapure emitters. But it is challenging to synthesize CsPbCl3 nanocrystals with sufficient stability, which impedes their application in light-emitting devices. In this work, we report a facile phosphoryl-chemistry-mediated synthesis approach to synthesizing stable CsPbCl3 nanocrystals, in which the phenylphosphonic dichloride (PhPOCl2) precursor is employed. In addition to the high reactivity of the P–Cl bond of PhPOCl2 for providing adequate Cl, the derived P=O with good proton affinity facilitates the formation of a distinct nanocrystal surface with the nonprotonated oleylamine (OLA) ligand. Accordingly, the L-type-ligand-capped CsPbCl3 nanocrystals exhibited not only bright luminance but also good stability that endured repeated purification up to 10 cycles. Based on the stable CsPbCl3 nanocrystals, we achieved violet LEDs with extremely narrow electroluminescence spectra (full width at half-maximum ≈ 10.6 nm).

A rigidly adhered nitrogen-doped BiVO4 photoanode with a narrow band gap energy (Eg = 2.35 eV) for water oxidation was developed to attain the IPCE value of 35.1% at 440 nm which is among the highe...

The exploration of narrow-emitting phosphors in the red, green, and blue spectral region is of great significance for improving the color gamut of liquid-crystal displays (LCD). In this work, a nar...

To overcome the problem that Bi3+-activated phosphors suffer from, it is an urgent need to realize narrow-band light emission of Bi3+-activated phosphors, which not only improves their luminescence...

Molybdenum diselenide (MoSe2) is a promising gas sensing material due to its large surface-to-volume ratio, narrow band gap, and excellent absorptions. However, MoSe2-based gas sensors possess infe...

Over the last decade, narrow-band emitters have been recognized as key enablers for light emitting diodes (LEDs) backlights in liquid-crystal displays (LCDs) by competing with other display technologies. Today, efforts have been devoted to the exploration of narrow-band green/red luminescent materials with high quantum efficiency and excellent stability to optimize the performance of LED backlights. This review first presents an overview of the significant progress made in the development of narrow-band emitters used in LED backlights for LCDs with the emphasis on the versatile materials databases from doped phosphors to luminescent II–VI, III-V semiconductor quantum dots, and the recent halide perovskites nanocrystals and bulk metal halides. Subsequently, the correlation of structure-luminescence properties, and the device performance optimization of these emitters have been analyzed. The focus is placed on summarizing and comparing the remarkable examples of outdated and new narrow-band luminescent materials as potential candidates in LED backlights. Finally, the outlooks and challenges in discovering new narrow-band emitters have been proposed.

Currently, high-performance organic solar cells (OSCs) are mainly composed of narrow band gap (NBG) nonfullerene acceptors and medium band gap (MBG) polymer donors, whereas the solar cells based on...

Organic light-emitting diodes utilizing thermally activated delayed fluorescence sensitizers and multiple-resonance (MR) dopants may simultaneously offer high efficiencies and narrow-band emissions...

Metamaterials are designed and manufactured artificially to manifest intriguing physical concepts and achieve unusual potential applications. However, the exotic properties of metamaterials normally originate from the resonance mechanism of artificial atoms, thus inevitably limited in narrow band and hindering their practical applications. Here, we numerically design and experimentally verify a novel tunable dielectric metamaterial based on strontium titanate artificial atoms to alleviate the bandwidth restriction of resonance metamaterial. By control of the magnetic resonance with the electric resonance, the tunable dielectric metamaterial can broaden the practical applications of metamtaterials and play an important role in all-optical communication devices.

The semitransparent flexible organic solar cell takes advantages of flexibility, transparency, color adjustment property, which is more conducive to integrate on buildings and mobile terminals. Ascribing to the developments of narrow band gap donors and the new non-fullerene acceptors, the power conversion efficiency of semitransparent flexible organic solar cells has been achieved 10% to 12% with average visible transmittance of 17% to 21%. This review summarizes the molecular design of the most representative active layer materials, and discusses the characterization of semitransparent parameters paradigms, then we discuss how to optimize the device in combination with optical simulation, and finally list the recent development of semitransparent flexible electrodes of ITO-free organic solar cells, and give our perspectives on the next step direction.

This work is the continuation of our previous work entitled "Investigations on optical, material and electrical properties of aSi:H and aSiGe:H in making proposed n+aSi:H/iaSi:H/p+aSiGe:H graded band gap solar cells." In this work, we present an additional bottom layer made of increased germanium content: aSi0.64Ge0.36:H to the previously recommended p+aSi:H/i-aSi:H/n+aSi0.73Ge0.27:H photovoltaic cell to strengthen the absorption spectrum and thereby boosting the attainment of the solar cell. Moreover, the overall active layer thickness is reduced from 430 nm of previous work to 395 nm of proposed work. This work includes the fabrication of samples of epitaxially grown aSiGe:H thin films of varying band gap made with Plasma Enhanced Chemical Vapour Deposition (PECVD) technique succeeded by their characterisation. The establishment of band gap tailoring by varying the germane (GeH4) gas flow rate is thoroughly investigated through optical characterisation. The growth chemistry of PECVD made aSi0.64Ge0.36:H layer has been analysed and the presence of respective radicals has been verified using Fourier Transform Infra Red (FTIR) spectroscopy. In accordance with the measured band gaps, p+ aSi:H/i-aSi:H/n+aSi0.73Ge0.27:H/naSi0.64Ge0.36:H solar cell has been proposed. A comprehensive inquiry on optimisation of the recommended structure has been made by varying the optical band gap and thickness of the bottom most aSi0.64Ge0.36:H layer of the structure. All the cell parameters including open circuit voltage (Voc), short circuit current density (Jsc), maximum power point voltage (Vm), maximum power point current density (Jm), Fill factor (FF) and conversion efficiency (η) has been calculated using SCAPS1D solar simulator. Furthermore, C–V characteristics and Mott-Schottky plot of the proposed structure has been evaluated. The introduction of narrow band gap amorphous silicon germanium (aSi0.64Ge0.36:H) at the bottom has remarkably enhanced Jsc and η to 15.54 mA/cm2 and 15.15% respectively, which is better compared to reported amorphous silicon photovoltaic cells having single junction.

This paper presents analytic and numerical modelling of a MEMS electrodynamic micro-sensor of dynamic pressure. Two coaxial planar inductors of different diameters are used in the proposed micro-sensor design. Using finite element analysis, the diaphragm resonant frequency and dynamic displacements are evaluated for different diaphragm thicknesses. Then, the total sensitivity is deduced by coupling different physical domains which contribute in the micro-sensor operation. A lumped element model is built in order to study the micro-sensor sensitivity and define the dynamic performance for different resonant frequencies. This model shows that the best sensitivity, within the mV/Pa range, is obtained around the resonant frequency when operation in the audible frequency range, and decreases to the uV/Pa range for ultrasonic frequencies. The obtained sensitivity curves prove that the undamped inductive micro-sensor can offer high pressure sensitivity within a narrow frequency bandwidth.

Complex bismuth chalcogenides are narrow band gap semiconductors with intrinsic low thermal conductivity, which exhibit high potential as highly efficient thermoelectric materials. Here, we assess ...

Incorporation of compact spectroscopic near-infrared (NIR) light detectors into various wearable and handheld devices opens up new applications, such as on-the-spot medical diagnostics. To extend beyond the detection window of silicon, i.e., past 1000 nm, organic semiconductors are highly attractive because of their tunable absorption. In particular, organic NIR wavelength-selective detectors have been realized by incorporating donor:acceptor thin films, exhibiting weak intermolecular charge-transfer (CT) absorption, into an optical microcavity architecture. In this work, the alkyl side chains of the well-known PBTTT donor polymer are replaced by alkoxy substituents, hereby redshifting the CT absorption of the polymer:PC61BM blend. It is shown that the unique fullerene intercalation features of the PBTTT polymer are retained when half of the side chains are altered, hereby maximizing the polymer:fullerene interfacial area and thus the CT absorption strength. This is exploited to extend the detection range of organic narrow-band photodetectors with a full-width-at-half-maximum of 30–38 nm to wavelengths between 840 and 1340 nm, yielding detectivities in the range of 5 × 1011 to 1.75 × 1010 Jones, despite the low CT state energy of 0.98 eV. The broad wavelength tuning range achieved using a single polymer:fullerene blend renders this system an ideal candidate for miniature NIR spectrophotometers.

This study presents a kind of healthy lighting which provides $\boldsymbol{Ra=97}$ with extremely high R9 up to 99 with least efficiency tradeoff due to the narrow band emission from CdSe/Zn x Cd 1 -xS/ZnS nanorods with high solid-state QY, as well as low blue portion for the whole spectrum.

In this paper, we theoretically analyze and design a dual-narrowband terahertz (THz) absorber based on a hole array drilled into a metallic slab. A very high-quality factor (Q) is achieved at both of the resonance frequencies. A circuit model-based approach is developed for the analysis and design of the proposed absorber. The absorption peaks occur at 2.46 and 3.75 THz frequencies with 98% and 96% absorptions at normal incidence, respectively. The achieved quality factors are 149 and 144, at 50% absorbance for the two absorption bands, respectively.

We present the results of theoretical and experimental studies of the resonant properties of a single cell of a receiving system based on cold-electron bolometers (CEBs) with a double-slot antenna and curved coplanar lines, which is intended for receiving a signal in the range 220–240 GHz with a bandwidth of 5%. The resonant properties of a CEB located on the cryostat plate with a temperature of 0.3 K, are measured using an oscillator based on high-temperature superconductor (HTS) of yttrium barium copper oxide (YBCO), placed inside the same cryostat on a plate with a temperature of 4 K, which allows one to obtain smooth amplitude-frequency characteristics.

Nowadays, obtaining photocatalysts with a narrow band gap that can degrade contamination under visible light has been a hot topic in the field of environmental protection. In this report, the S-dop...

First time study for development of relationship between design and fabrication of thin film narrow-pass filters simulated using the Essential Macleod optical coating design program and verified through experimental data. In thin film narrow band-pass filter's design, can design better filter by changing some parameters, but the theoretical designs are often difficult to achieve. The sensitivity of thin film narrow band-pass filters are mainly influenced by the refractive index of cavity layers, number of mirror layers, interference order and number of cavities. Based on analysis of all these aspects, laws of influence are obtained. A narrow band-pass filter with super wide rejection band was designed and fabricated to verify the simulation results, showing a good agreement between the experimental and theoretical observations.

This Letter reports the localization of optical fields in dielectric nanopillar arrays on a metal film. Large-area arrays of tall (>450 nm) polymer pillars were patterned on an optically thick gold...

Efficient separation and utilization of the photoinduced charge is crucial to the photocatalytic H2 generation reaction, especially for semiconductors with narrow band gap energies that suffer seve...

While photoelectrochemical (PEC) water splitting is a very promising route toward zero-carbon energy, conversion efficiency remains limited. Semiconductors with narrower band gaps can absorb a much greater portion of the solar spectrum, thereby increasing efficiency. However, narrow band gap (∼1 eV) III-V semiconductor photoelectrodes have not yet been thoroughly investigated. In this study, the narrow band gap quaternary III-V alloy InGaAsP is demonstrated for the first time to have great potential for PEC water splitting, with the long-term goal of developing high-efficiency tandem PEC devices. TiO

The use of red phosphors with low light-scattering loss could improve the luminous efficacy and color rendering of white-light-emitting diodes (LEDs). Thus, the discovery of such phosphors is highl...

Innovative materials for phosphor converted white light-emitting diodes are in high demand owing to the huge potential of the light-emitting diode technology to reduce energy consumption worldwide. As the primary blue diode is already highly optimized, the conversion phosphors are of crucial importance for any further improvements. We report on the discovery of the high performance red phosphor Sr[Li2Al2O2N2]:Eu2+ meeting all requirements for a phosphor’s optical properties. It combines the optimal spectral position for a red phosphor, as defined in the 2016 Research & Development-plan of the United States government, with an exceptionally small spectral full width at half maximum and excellent thermal stability. A white mid-power phosphor-converted light-emitting diode prototype utilising Sr[Li2Al2O2N2]:Eu2+ shows an increase of 16% in luminous efficacy compared to currently available commercial high colour-rendering phosphor-converted light-emitting diodes, while retaining excellent high colour rendition. This phosphor enables a big leap in energy efficiency of white emitting phosphor-converted light-emitting-diodes. Developing innovative materials for reduced energy consumption in phosphor converted white light-emitting diodes remains a challenge. Here, the authors report a narrow band red-emitting oxonitride material with a highly symmetrical Sr2 + coordination for energy efficient white light-emitting diodes.

Here, using the safety raw materials Li3N, Sr3N2 and Eu2O3 instead of LiAlH4, SrH2 and EuF3 (besides AlN), the nitride phosphor SrLiAl3N4:Eu2+ (SLA:Eu2+) was synthesized in the glove box (O2

The performance of metamaterial is limited to a designed narrow band due to its resonant nature, it is highly desirable to incorporate active inclusions in metamaterials to extend the operation bandwidth. This review summarizes the development in realizing the tunability of electromagnetic response in metamaterials incorporated with nematic liquid crystal (LC). From rigorous comparison, it is found that the anisotropic property of nematic LC is essential in predicting the influence of LC molecular director orientation on the resonant frequency of metamaterials. By carefully designing the metamaterials and properly infiltrating LC, the operation frequency of single/double negative parameters of metamaterials can be dynamically modulated with remarkable red/blue-shift, depending on the LC molecular orientation angle. Moreover, the recent liquid crystal-based developments and novel applications are investigated and highlighted.

Organic solar cells (OSCs) that contain small molecules only were prepared with FG1 as the donor, a narrow band gap non-fullerene acceptor MPU4, and a wide band gap PC71BM. The OSCs based on optimi...

Based on the revolutionary metamaterials, this paper investigates the frequency behavior of modified split ring resonators (SRRs) to create a sensor for measuring electrical parameters of dielectrics. Focused on simulations, the best cases of SRRs configurations (including the number of double SRRs and strips that were added) will be identified in order to obtain a good result in frequency which is translated into a good selectivity (narrow band) and a peak sharp enough to accurately read the frequency. Moreover, changes will be made to the substrate, both for dielectric characteristics, varying its loss tangent, as well as for its thickness. Using the shift of the resonance frequency method, the best configuration will be selected and analyzed for a sensor application.

Designing various nanostructures to achieve narrowband light reflection resonances is desirable for optical sensing applications. In this work, we theoretically demonstrate two narrowband light reflection resonances resulting from the excitations of the zero-order transverse magnetic (TM) and transverse electric (TE) waveguide modes, in a waveguide structure consisting of an Au sphere array on an indium tin oxide (ITO) spacer on a silica (SiO2) substrate. The positions of the light reflection resonances can be tuned easily, by varying the array periods of gold (Au) spheres or by changing the thickness of the ITO film. More importantly, the light reflection resonances have a very narrow bandwidth, the full width at half maximum (FWHM) of which can be reduced to only several nanometers for the zero-order TM and TE waveguide modes. The conventionally defined performance parameters of sensors, sensitivity (S) and figure of merit (FOM), have quite high values of about 80 nm/RIU and 32, respectively, in the visible wavelength range.

Deep-penetration fluorescence imaging in the second near-infrared (NIR-II) window heralds a new era of clinical surgery, in which high-resolution vascular/lymphatic anatomy and detailed cancerous tissues can be visualized in real time. Described here is a series of polymethine-based semiconducting polymers with intrinsic emission maxima in the NIR-IIa (1300-1400 nm) window and absorption maxima ranging from 1082 to 1290 nm. These polymers were prepared as semiconducting polymer dots (Pdots) in aqueous solutions with fluorescence quantum yields of 0.05-0.18 %, and they demonstrate promising applications in noninvasive through-skull brain imaging in live mice with remarkable spatial resolution as well as signal-to-background contrast. This study offers a platform for future design of NIR-IIa or even NIR-IIb emitting Pdots.

We design and manufacture a narrow-band photodetector that can perform high-gain detection of 2.4 GHz RF signals and strongly suppress noise and harmonics, which is proved to be better applied to optical fiber RF transfer.

Diffractive photonic devices manipulate light via local and nonlocal optical modes. Local devices, such as metasurfaces, can shape a wavefront at multiple selected wavelengths, but inevitably modify light across the spectrum; nonlocal devices, such as grating filters, offer great frequency selectivity but limited spatial control. Here, we introduce a rational design paradigm using quasi-bound states in the continuum to realize multifunctional nonlocal devices: metasurfaces that produce narrowband spatially tailored wavefronts at multiple selected wavelengths and yet are otherwise transparent., 15 pages, 4 figures

Quasi-two-dimensional perovskite multiple quantum wells (MQWs) have garnered attention on account of their good stability in comparison with three-dimensional analogs for light-emitting diode (LED) applications, but they exhibit a declined photoluminescence quantum yield (PLQY) for the backlight display technology. Herein, we report an in situ process by introducing layered materials as substrates to prepare the perovskite MQW powder and utilize hexagonal boron nitride (h-BN) as an example to investigate the luminescence characteristics and mechanism of h-BN@(PMA)