High Spectral Selectivity Research Articles

A gradient nanoporous radiative cooling ceramic with high spectral selectivity

Radiative cooling offers a sustainable solution for building space cooling. Cooling ceramics are receiving increasing attention due to their exceptional mechanical properties and environmental resistance. However, the limited spectral selectivity hinders their cooling temperatures, particularly in hot and humid climates. This study presents a gradient nanoporous magnesium oxide (MgO) ceramic with excellent spectral selectivity (1.69). It exhibits a high solar reflectance (0.96) and a selective long-wave infrared (LWIR) emittance (0.95), achieving a sub-ambient temperature reduction throughout the day in Changsha. Energy simulations demonstrate that the cooling ceramic can effectively alleviate cooling demands in hot and humid climates. The exceptional mechanical properties and environmental resistance ensure the long-term durability of the cooling ceramic. Moreover, the simple fabrication process and remarkable cleaning capability significantly reduce its cost, making it a highly promising candidate for large-scale radiative cooling applications in buildings.

High-responsivity photoelectrochemical ultraviolet photodetector based on SnO2 nanosheets-Ga2O3

Abstract Tin oxide (SnO2) has garnered significant attention for its high spectral selectivity when used as an ultraviolet photodetector. In this study, SnO2 nanosheets (NSs) were synthesized via a hydrothermal method, followed by spin-coating a layer of Ga2O3 thin film to construct a heterojunction photoelectrochemical ultraviolet photodetector (PEC UV PD). Initially, we investigated the effect of precursor composition on the properties of the Ga2O3 thin films. It was observed that the thickness of the films increased with higher precursor concentrations, while the optical bandgap decreased. Based on these findings, we successfully fabricated the SnO2 NSs-Ga2O3 PEC UV PD. Electrochemical analysis revealed that as the precursor concentration used for spin-coating Ga2O3 increased, the device's responsivity and detectivity initially increased and then decreased. After optimization, the device prepared with a 0.2M Ga(NO3)3 solution spin-coated on SnO2 exhibited excellent spectral selectivity (R 265nm/R 420nm ~ 4472), a responsivity of 4.86 mA W-1, and a detectivity of 2.72×109 Jones. This study demonstrates that coating Ga2O3 is an effective approach to constructing high-performance SnO2-based UV PDs.

Calibration-free infrared absorption spectroscopy using cantilever-enhanced photoacoustic detection of the optical power

We report on sensitive tunable laser absorption spectroscopy using a multipass gas cell and a solid-state photoacoustic optical power detector. Unlike photoacoustic spectroscopy (PAS), this method readily allows a low gas pressure for high spectral selectivity and a free gas flow for continuous measurements. Our photoacoustic optical power detector has a large linear dynamic range and can be used at almost any optical wavelength, including the middle infrared and THz regions that are challenging to cover with traditional optical detectors. Furthermore, our approach allows for compensation of laser power drifts with a single detector. As a proof of concept, we have measured very weak CO2 absorption lines at 9.2 µm wavelength and achieved a normalized noise equivalent absorption (NNEA) of 2.35·10−9 Wcm−1Hz−1/2 with a low-power quantum cascade laser. The absolute value of the gas absorption coefficient is obtained directly from the Beer-Lambert law, making the technique calibration-free.

Surface Reconstruction of La0.5Sr0.5CoO3-δ Ceramic toward High Solar Selectivity for High-Temperature Air-Stable Solar-Thermal Conversion.

As a key device for solar energy conversion, solar absorbers play a critical role in improving the operating temperature of concentrated solar power (CSP) systems. However, solar absorbers with high spectral selectivity and good thermal stability at high temperatures in air are still scarce. This study presents a novel surface reconstruction strategy to improve the spectral selectivity of La0.5Sr0.5CoO3-δ (LSC5) for enhanced CSP application. The strategy could efficiently enhance the solar absorptance due to the existence of a high-absorption thin layer composed of nanoparticles on the LSC5 surface. Meanwhile, the crystal facet with low emittance on the LSC5 surface was exposed. Thus, the LSC5 that underwent surface reconstruction achieved a higher solar absorptance (∼0.75) and lower infrared emittance (∼0.19) compared to the original LSC5 (0.63/0.21), representing an improvement of nearly 32%. Additionally, the surface reconstructed LSC5 demonstrated a lower infrared thermographic temperature and a higher solar-thermal conversion equilibrium temperature compared to those of LSC5 and SiC. Moreover, the reconstructed LSC5 could maintain stable performance up to 800 °C in air, which might simplify the complexity of the CSP systems. The surface reconstruction strategy provided a new method to optimize the spectral selectivity of high-temperature stable ceramics, contributing to advancements in solar energy conversion technologies.

Role of Histidine 310 in Amydetes vivianii firefly luciferase pH and metal sensitivities and improvement of its color tuning properties.

Firefly luciferases emit yellow-green light and are pH-sensitive, changing the bioluminescence color to red in the presence of heavy metals, acidic pH and high temperatures. These pH and metal-sensitivities have been recently harnessed for intracellular pH indication and toxic metal biosensing. However, whereas the structure of the pH sensor and the metal binding site, which consists mainly of two salt bridges that close the active site (E311/R337 and H310/E354), has been identified, the specific role of residue H310 in pH and metal sensing is still under debate. The Amydetes vivianii firefly luciferase has one of the lowest pH sensitivities among the group of pH-sensitive firefly luciferases, displaying high bioluminescent activity and special spectral selectivity for cadmium and mercury, which makes it a promising analytical reagent. Using site-directed mutagenesis, we have investigated in detail the role of residue H310 on pH and metal sensitivity in this luciferase. Negatively charged residues at position 310 increase the pH sensitivity and metal sensitivity; H310G considerably increases the size of the cavity, severely impacting the activity, H310R closes the cavity, and H310F considerably decreases both pH and metal sensitivities. However, no substitution completely abolished pH and metal sensitivities. The results indicate that the presence of negatively charged and basic side chains at position 310 is important for pH sensitivity and metals coordination, but not essential, indicating that the remaining side chains of E311 and E354 may still coordinate some metals in this site. Furthermore, a metal binding site search predicted that H310 mutations decrease the affinity mainly for Zn, Ni and Hg but less for Cd, and revealed the possible existence of additional binding sites for Zn, Ni and Hg.

Self‐Assembly PbS Quantum Dot‐Conjugated Polymer Hybrid‐Layered Phototransistor Enables SWIR Photodetection with High Detectivity

AbstractLead sulfide colloid quantum dots (PbS QDs) offer great opportunities to revolutionize large‐area short‐wave infrared (SWIR) detection technologies due to high absorption coefficients and spectral selectivity. However, a critical issue for QDs‐based SWIR detectors is high dark current noise due to thermal carriers and the large amounts of surface defect states induced by the ligand exchange process, which hinders the improvement of the room temperature detectivity and linear dynamic range. Herein, it is demonstrated that these dilemmas can be overcome by adopting a novel hybrid‐layered phototransistor device architecture composed of a self‐assembly high‐mobility organic conduction channel and a bulk heterojunction infrared absorber containing PbS QDs as sensitizers. Strong photo absorption in the photoactive layer creates photogenerated charges that are transferred to the conduction channel, where they recirculate many times due to the long trapped‐electron lifetime in the photoactive layer and the high carrier mobility of the channel. Therefore, low dark current noise and high photoconductive gain are achieved by both electrical gating and photodoping for carrier‐density modulation of phototransistors. Finally, an optimized SWIR phototransistor device with a low room‐temperature dark current of 7 pA and a high detectivity of 8 × 1012 Jones under 1650 nm light illumination is demonstrated.

A solar-blind vacuum-ultraviolet photodetector based on free-standing lamellar aluminum nitride single crystal

High-quality aluminum nitride (AlN) crystals are the key material for the development of high-performance solid-state solar-blind vacuum-ultraviolet (VUV) photodetectors. However, the commonly used epitaxial method to grow AlN crystals would limit this development due to the existence of indispensable substrates. This study addresses this issue using free-standing lamellar AlN single crystals that are grown using the physical vapor transport method. The large lateral dimension of the crystal enables the construction of an Au-AlN-graphene van der Waals heterojunction, which can function as a vertical VUV photodetector with the graphene serving as the light window. The asymmetric junctions formed on the two sides of the crystal and the limited penetration of the VUV endow the device with a bias polarity-dependent photoresponse feature arising from different photoelectric processes. Furthermore, the device demonstrates a high responsivity of 5.77 A W−1 and a high specific detectivity of 1.71 × 1013 cm Hz1/2 W−1 under the illumination of a 193 nm laser. The high crystallinity of the AlN guarantees a high spectral selectivity of responsivity with a 193 nm/280 nm rejection ratio of 3 × 102. This work would inspire the development of wide-bandgap-semiconductor-based VUV photodetectors in terms of methodology and mechanism.

A fluorescent probe based on carbon quantum dots with spectral selectivity for sensitive detection of Cr(VI) and Hg(II) in environmental waters

In this paper, fluorescent carbon dots were prepared by hydrothermal method using 3,5-dihydroxybenzoic acid and l-Arginine as precursors. The synthesized CDs have excitation-dependent emission with emission peaks at 354 nm and 460 nm, corresponding to the optimal excitation wavelengths of 295 nm and 330 nm, respectively. CDs have good dispersion and resistance to photobleaching in aqueous solution, and can maintain stable fluorescence in highly concentrated salt environment. Based on the inner filter effect, Cr(VI) with strong absorption can shield the excitation light of CDs at 295 nm and absorb the emission fluorescence at 354 nm simultaneously. Due to the intermolecular electrostatic interaction, Hg(II) can coordinate with CDs surface groups and cause static quenching, which significantly reduces the fluorescence intensity of CDs emitted at 460 nm. The linear ranges were 0.1–2 μM and 0.4–5 μM for Cr(VI) and Hg(II) detection, respectively, and limits of detection were 0.024 μM and 0.084 μM. Additionally, the probe was successfully applied to tap water and lake water samples. With high sensitivity and spectral selectivity, this sensing strategy realized the detection of two heavy metal ions by a single fluorescent probe, demonstrating its great potential in the field of environmental metal analysis.

Novel Two‐Dimensional NbWO6 Nanosheets for High Performance UV Photodetectors

AbstractA new ultraviolet photodetector (UV PD) is successfully fabricated based on 2D NbWO6 (NWO) nanosheets for the first time, which is synthesized by a facile solid‐state reaction, ion exchange and liquid exfoliation process. The NWO nanosheet‐based PDs exhibit excellent UV detecting performance at 1 V at 290 nm, high responsivity (378 A W−1), high external quantum efficiency (EQE, 1.6 × 104%), high spectral selectivity (R290/R400 = 8.84 × 103) and fast speed (1.05/88 ms). Furthermore, the NbWO6 nanosheets film based PD shows great potential for the application in UV image sensing. This work provides a feasible strategy for the development of new UV PDs based on other potential layered niobates.

Spectral-selective near-infrared photothermal detector enabled by integrating graphene-Au nanorods hybrid on a thermistor

Near-infrared (NIR) detectors with high sensitivity and spectral selectivity are highly desired in various applications. In this work, a photothermal detector with high NIR sensitivity and spectral selectivity was developed by simply modifying a photothermal layer of reduced graphene oxide-Au nanorods (rGO-AuNRs) hybrid on a thermistor, which can convert the light energy into heat and reflect as resistance changes of a thermistor. Owing to the plasmon coupling of the two materials, the obtained rGO-AuNRs hybrid not only has remarkable photothermal conversion efficiency but also exhibits dependence on spectral response. Thus, benefiting from the excellent performance of the hybrid, the fabricated detector is sensitive to illumination in the wavelength range from 700 to 1000 nm with the highest photoresponsivity of 2.50 × 105 Ω·W−1. The photothermal detector presented in this work will provide a simple and inexpensive alternative for NIR detector development.

Photonic crystals built by time in ancient Roman glass

Ancient glass objects typically show distinctive effects of deterioration as a result of environmentally induced physicochemical transformations of their surface over time. Iridescence is one of the distinctive signatures of aging that is most commonly found on excavated glass. In this work, we present an ancient glass fragment that exhibits structural color through surface weathering resulting in iridescent patinas caused by silica reprecipitation in nanoscale lamellae. This archaeological artifact reveals an unusual hierarchically assembled photonic crystal with extremely ordered nanoscale domains, high spectral selectivity, and reflectivity (~90%), that collectively behaves like a gold mirror. Optical characterization paired with nanoscale elemental analysis further underscores the high quality of this structure providing a window into this sophisticated natural photonic crystal assembled by time.

Two-dimensional perovskite NdNb2O7 for high-performance UV photodetectors by a general exfoliation and assembly strategy

Two-dimensional (2D) oxide perovskites show great promise as candidates for future optoelectronic devices. For the first time, we have successfully exfoliated 2D perovskite NdNb2O7 (NNO) nanosheets by a solid-state calcination and liquid-phase exfoliation method. The individual NNO nanosheet photodetector (PD) demonstrates outstanding performance in detecting UV light (260 nm, 3 V), including high responsivity (62 AW−1), high detectivity (6.7 *1012 Jones), high spectral selectivity (R260/R400= 9000), fast response speed (0.1/7.8 ms) and long-term stability. Furthermore, through a simple interface self-assembly technique, we have successfully achieved orderly and flat films of NNO nanosheets. The resulting film exhibits high transparency (>75 %) in the visible light range. The NNO film device demonstrates excellent performance after undergoing numerous bending tests. This work not only presents a new candidate for high-performance and high-stability UV photodetectors but also introduces a general exfoliation and assembly strategy.

Improved detection performance of self-driven InZnO / p-GaN heterojunction UV photodetector by lanthanum doping

By using the sol-gel spin-coating method, La-InZnO films with different La (0 at%, 2 at%, 4 at%, and 6 at%) doping concentrations were grown on p-GaN / sapphire film templates, and self-driven p-GaN / n-ZnO heterojunction ultraviolet (UV) detectors were prepared. The effects of La doping concentration on the microstructure, optical, and electrical properties of synthesized La-InZnO films were studied. In addition, the optical sensing characteristics and photoelectric response performance of four p-n heterojunction UV detectors were compared. La doping can decrease the content of oxygen vacancies. It also reduces the carrier concentration and mobility of the films. At zero bias voltage, the 2 at% doped device has the best performance, with a peak responsivity of 46 mA/W at 366 nm, a high spectral selectivity full width at half maximum (FWHM) of only 6.92 nm, and a fast response with the rise and decay times of 1.15 ms and 2.42 ms, respectively. This study demonstrates a feasible method for improving the performance of self-driven heterojunction UV detectors.

Self-powered solar-blind ultraviolet photodetectors with Ga2O3 nanowires as the interlayer

Solar-blind photodetectors are widely used in military, industrial and commercial fields. There is an urgent need to develop devices with high spectral selectivity, high performance and low energy consumption. Here, ultrafine β-Ga2O3 nanowires were synthesized on a n-Si substrate using chemical vapor deposition, and a self-powered solar-blind photodetector based on β-Ga2O3 nanowires cluster and n-Si were fabricated with PEDOT:PSS as a transparent conductive layer to spread the current. Additionally, PMMA was used as an insulating layer to prevent short circuiting of the device and the device fabrication process was described in detail. In the aforementioned PEDOT:PSS/Ga2O3NWs/Si double heterojunction device, Ga2O3 nanowires serve as vital spectral-selective materials for the solar-blind band. The significance of Ga2O3 nanowires as an interlayer within the device was explored by introducing nanowires with varying morphologies. The inclusion of Ga2O3 nanowires led to a substantial improvement in the device's responsivity within the solar-blind band, while the performance within the visible band remained relatively unchanged. Remarkably, at a wavelength of 250 nm, the device incorporating a cluster of Ga2O3 nanowires as the interlayer exhibited a responsivity of 26.8 mA/W, which is 44 times greater than that of the PEDOT:PSS/Si heterojunction device.

Minimax design of two-channel critically sampled graph QMF banks

We address here the issue of designing high spectral selectivity graph filter banks, which require high-degree polynomial approximation. To achieve sharp transition band roll required for high-selectivity, the minimax criterion is used in the design formulation. A constraint optimization method is used for the design process, and a spectral transformation is employed to circumvent the numerical problems that arise with high-degree polynomials. Using the transformation, approximation problem can be recast as an approximation problem with trigonometric polynomials. The transformed constraint optimization problem can be solved using the readily available sequential quadratic programming (SQP) method. High order filters, with low maximum approximation error (MAE) and low maximum reconstruction error (MRE), can be designed with this method. An algorithm is also developed that allows the user to choose design parameters that will give the lowest possible MRE. The method can also be adapted to trade-off between reconstruction quality and spectral selectivity of the resulting filter bank. The suite of techniques presented allow the user to easily shape the spectral response of the filters, to suit the application at hand. Numerous examples, with comparisons, will be presented to demonstrate the versatility of the proposed techniques. Applications to nonlinear approximation and denoising of graph signal will also be considered.

Different LED light intensity and quality change perennial ryegrass (Lolium perenne L.) physiological and growth responses and water and energy consumption.

Light intensity and spectral composition highly affect plant physiology, growth, and development. According to growing conditions, each species and/or cultivar has an optimum light intensity to drive photosynthesis, and different light spectra trigger photosynthetic responses and regulate plant development differently. For the maintenance of natural sports pitches, namely professional football competitions, turf quality is a key condition. Due to the architecture of most football stadiums, the lawns receive low intensities of natural light, so supplementary artificial lighting above the turf is required. The use of light-emitting diodes (LEDs) can have a higher cost-benefit ratio than traditional high-pressure sodium lamps. The continuous emission spectrum, combined with high spectral selectivity and adjustable optical power, can be used to optimize plant growth and development. Thus, perennial ryegrass (Lolium perenne L.) plants, commonly used for lawns, were primarily grown at three different intensities (200, 300, and 400 μmol m-2 s-1) of cool white light. Despite the higher water and energy consumption, 400 μmol m-2 s-1 maximizes the plant's efficiency, with higher photosynthetic rates and foliar pigment concentration, and more foliar soluble sugars and aboveground biomass accumulation. Then, it was evaluated the perennial ryegrass (Double and Capri cultivars) response to different spectral compositions [100% cool white (W), 80% Red:20% Blue (R80:B20), 90% Red:10% Blue (R90:B10), and 65% Red:15% Green:20% Blue (R65:G15:B20)] at 400 μmol m-2 s-1. Both cultivars exhibited similar responses to light treatments. In general, W contributed to the better photosynthetic performance and R90:B10 to the worst one. Water consumption and aboveground biomass were equal in all light treatments. R80:B20 allows energy savings of 24.3% in relation to the W treatment, showing a good compromise between physiological performance and energy consumption.

Fabrication of High-Performance Visible-Blind Ultraviolet Photodetectors Using Electro-ionic Conducting Supramolecular Nanofibers.

The detection of ultraviolet (UV) light is vital for various applications, such as chemical-biological analysis, communications, astronomical studies, and also for its adverse effects on human health. Organic UV photodetectors are gaining much attention in this scenario because they possess properties such as high spectral selectivity and mechanical flexibility. However, the achieved performance parameters are much more inferior than the inorganic counterparts because of the lower mobility of charge carriers in organic systems. Here, we report the fabrication of a high-performance visible-blind UV photodetector, using 1D supramolecular nanofibers. The nanofibers are visibly inactive and exhibit highly responsive behavior mainly for UV wavelengths (275-375 nm), the highest response being at ∼275 nm. The fabricated photodetectors demonstrate desired features, such as high responsivity and detectivity, high selectivity, low power consumption, and good mechanical flexibility, because of their unique electro-ionic behavior and 1D structure. The device performance is shown to be improved by several orders through the tweaking of both electronic and ionic conduction pathways while optimizing the electrode material, external humidity, applied voltage bias, and by introducing additional ions. We have achieved optimum responsivity and detectivity values of around 6265 A W-1 and 1.54 × 1014 Jones, respectively, which stand out compared with the previous organic UV photodetector reports. The present nanofiber system has great potential for integration in future generations of electronic gadgets.

High-Performance Solar-Blind UV Phototransistors Based on ZnO/Ga2O3 Heterojunction Channels.

High-performance phototransistor-based solar-blind (200-280 nm) ultraviolet (UV) photodetectors (PDs) are constructed with a low-cost thin-film ZnO/Ga2O3 heterojunction. The optimized PD shows high spectral selectivity (R254/R365 > 1 × 103) with a photo-to-dark current ratio of ∼104, a responsivity of 113 mA/W, a detectivity of 1.25 × 1012 Jones, and a response speed of 41 ms under 254 nm UV light irradiation. It is found that the gate electrode of a three-terminal phototransistor can amplify the responsivity and increase the photo-to-dark current ratio because of the different densities of field-induced electrons at different gate biases. In addition, the built-in electric field at the ZnO/Ga2O3 heterojunction interface can control the distribution of the photoinduced electrons and the total conductivity of the heterojunction, which can further enhance device performance. Together with the simple fabrication process, the achieved results suggest that the three-terminal ZnO/Ga2O3 heterojunction phototransistor is a promising candidate for highly sensitive solar-blind PDs.

Robust Si/Ge heterostructure metasurfaces as building blocks for wavelength-selective photodetectors

We present a design for silicon-compatible vertical Germanium pin photodiodes structured into all-dielectric metasurfaces. Proof-of-principle metasurfaces are fabricated on silicon-on-insulator wafers in a top-down process. Simulations and measurements of the spectroscopic properties, specifically the absorption, show high spectral selectivity, and absorption efficiencies as large as those in bulk Germanium layers with about four times the Ge layer thicknesses. Our metasurface structures can be tuned to the target wavelength through tailoring of the lateral geometry. Possible applications include spectroscopy and hyperspectral imaging, with several metasurfaces for different wavelength ranges integrated with readout circuitry into a low-cost electronic–photonic integrated circuit.

Plasmonic bound states in the continuum to tailor light-matter coupling.

Plasmon resonances play a pivotal role in enhancing light-matter interactions in nanophotonics, but their low-quality factors have hindered applications demanding high spectral selectivity. Here, we demonstrate the design and 3D laser nanoprinting of plasmonic nanofin metasurfaces, which support symmetry-protected bound states in the continuum up to the fourth order. By breaking the nanofins' out-of-plane symmetry in parameter space, we achieve high-quality factor (up to 180) modes under normal incidence. The out-of-plane symmetry breaking can be fine-tuned by the nanofins' triangle angle, opening a pathway to precisely control the ratio of radiative to intrinsic losses. This enables access to the under-, critical, and over-coupled regimes, which we exploit for pixelated molecular sensing. We observe a strong dependence of the sensing performance on the coupling regime, demonstrating the importance of judicious tailoring of light-matter interactions. Our demonstration provides a metasurface platform for enhanced light-matter interaction with a wide range of applications.