Visible Spectral Region Research Articles

A systematic study of Surface Plasmon Enhanced Electric Field in Nanoparticle Dimers for UV Plasmonics

AbstractSurface plasmon mediated electric field enhancement in the dimer arrangement of Al, Ag and, Au nanoparticles using multipole spectral expansion (MSE) approach has been studied. MSE method has flexibility and simplicity in extending the approach to treat an arbitrary arrangement of nanoparticles by solving corresponding general eigenvalue problem. The field enhancement behavior of Al, Ag, and Au nanoparticle dimers has been investigated, covering UV–VIS spectral range. The role of embedding medium, particle–particle separation, and the metal type were studied. The resonance wavelength showed the red shift with increasing the dielectric constant of the ingrained material. The red shift with increasing particle size and the dielectric constant of embedded or ingrained medium has been studied. This study was used to design plasmonic nanoparticle dimer with resonant optical response at crucial wavelengths in UV–VIS spectral region.

Testing the utility of the resampled nSight-2 spectral configurations in discriminating wetland plant species using Random Forest classifier

Hyperspectral sensors have the potential of discerning subtle differences among wetland plant species. Assessment of wetland plant species is critical for the effective management of wetland ecosystems. We evaluated the utility of the forthcoming nSight-2 hyperspectral sensor in wetland plant species differentiation, by testing the utility of its spectral settings and compared its performance to EnMap and WorldView-2 sensors in classifying four dominant wetland plant species in Verloren Vallei Nature Reserve, South Africa. For this purpose, we used the Random Forest classifier and field spectrometer data of various wetland plant species. The results showed that the spectral settings of nSight-2, EnMap, and WorldView-2 yielded high overall accuracies of 84.09%, 81.82% and 77.77%, respectively. The best accuracies were achieved with spectral bands sampled across the visible, red-edge and near-infrared spectral regions. Overall, the findings demonstrate the potential of the upcoming hyperspectral satellite missions for wetland ecosystems monitoring and management.

Calcination Temperature Induced Structural, Optical and Magnetic Transformations in Titanium Ferrite Nanoparticles

Titanium ferrite represents one of the most promising magnetic materials that exhibits optical absorption in both ultraviolet and visible spectral regions with a range of applications in photocatalysis, giant magnetoresistance, sensors, high-frequency modern power supplies, etc. Here in the present work, we report synthesizing titanium ferrite NPs via the co-precipitation method. As obtained ferrite nanopowders were characterized using XRD, UV-Visible absorption, Raman scattering, and variable sample magnetometer techniques. The crystalline size of NPs lies between 35 to 50 nm. The as-obtained nanopowder samples were calcined at 200, 500, 800 °C temperatures, and the resulting change in the optical, structural, and magnetic properties are investigated. The saturation magnetization of 500 °C calcined sample is higher than that calcined at 200 °C, but the magnetization value drastically becomes reduced for powder calcined at 800 °C temperature. The results of the present work can be used to understand the effects of annealing temperature on the structural and magnetic properties of other ferrite nanomaterials.

TROPOMI-Retrieved Underwater Light Attenuation in Three Spectral Regions in the Ultraviolet and Blue

Ultraviolet (UV) radiation plays an important role in the ocean for the biogeochemical cycling through photooxidation of colored dissolved organic matter and metals. It also influences the release of trace gases into the atmosphere. Understanding interaction and climate feedback mechanisms of these processes requires global long-term monitoring of UV radiation in the ocean. Ocean color sensors provide the diffuse attenuation coefficient for downwelling solar irradiance (Kd) as an estimate for the mean light penetration depth in the surface ocean. However, Kd products for the UV spectral range are currently only indirectly inferred from measurements in the visible spectral region. We exploit the UV and visible wavelengths of the TROPOMI sensor onboard Sentinel-5P to directly infer diffuse attenuation coefficients in the UV and blue spectral range. Our approach is based on Differential Optical Absorption Spectroscopy in combination with radiative transfer modeling which has been used in earlier studies to successfully derive Kd in the blue from the vibrational Raman scattering (VRS) signal. VRS was detected in the backscattered radiances of TROPOMI-like sensors at a spectral resolution around 0.5 nm. We adapt this method for the TROPOMI sensor and more spectral regions to obtain two novel Kd products in the UV range (312.5–338.5 nm and 356.5–390 nm), additionally to the blue Kd (390–423 nm). One month of TROPOMI data show high sensitivity to retrieve VRS (fit errors <15%). The resulting Kd values in the UV and blue agree reasonably (RMSD <0.31 m−1) with in-situ data measured during a transatlantic cruise. Kd-blue compared to wavelength-converted Kd(490) products from OLCI and OC-CCI shows that the differences between the three data sets are within uncertainties given for the OC-CCI product. TROPOMI Kd-blue results have higher quality and much higher spatial coverage and resolution than previous ones from SCIAMACHY, GOME-2, and OMI. Perspectively, global TROPOMI Kd products, once thoroughly validated, can be used as input for modeling, e.g., photochemical reaction rates of climatically important compounds and inhibition of primary productivity.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Solar absorption characteristics of SiO2@Au core-shell composite nanorods for the direct absorption solar collector

It has been reported that plasma nanofluids are beneficial to improve the performance of a direct absorption solar collector (DASC). For this purpose, the solar absorption of gold sphere nanoparticles (NPs) in the near-infrared spectral region and gold nanorods in the visible spectral region needs to be focused. Based on this issue, we propose a core-shell composite nanorod and investigate its optical properties to illustrate its potential for improving the solar absorption efficiency of the DASC. The results show that the core-shell composite nanorod improves the absorption efficiency both in the near-infrared and visible spectral region. Further study reveals that the absorption mechanism of the composite nanorods can be attributed to localized surface plasmon resonance (LSPR) and propagating surface plasmon resonance (PSPR). In addition, in view of the discussion about the geometrical size of composite nanorods and the calculation of composite nanorod suspension, the solar absorption efficiency can be as high as 95.3%. Notably, the imperfect shell during the experimental synthesis will greatly reduce the absorption capacity of the composite nanorods. The results show that the core-shell composite nanorod has great potential in the DASC applications.

Exploring the potential of Pr3+:LiY0.3Lu0.7F4 mixed crystal for diode-pumped watt-level continuous-wave lasers in the visible region

By partially substituting the Y3+ ions with Lu3+ ions, the widely investigated Pr:LiYF4 single crystal has been formated into Pr:LiY0.3Lu0.7F4 mixed crystal. In this work, we report the recent progress on diode-pumped continuous-wave Pr:LiY0.3Lu0.7F4 lasers in visible spectral region. Using a diode double-end pumping geometry, we have achieved red (∼640 nm), orange (∼607 nm), green (∼523 nm) and deep red (∼721 nm) lasers with maximum output powers and slope efficiencies of (3.28 W, 35.9%), (1.79 W, 19.8%), (1.61 W, 18.0%) and (1.56 W, 20.8%), respectively. The orange and deep red lasers are first demonstrated in the Pr:LiY0.3Lu0.7F4 mixed crystal, to the best of our knowledge. Moreover, the results represent the best laser performance for Pr3+ mixed crystal lasers. Researches on Pr3+ mixed crystals and their corresponding lasers are still on their initial stages, which could provide some new opportunities for the generation of high-power continuous-wave visible lasers and more importantly for the generation of femtosecond ultrashort pulsed visible lasers that is indeed very on demand.

Template‐Guided C8‐BTBT/MAPbBr3/C8‐BTBT Heterostructures for Broadband Bipolar Phototransistors

AbstractBipolar junction transistor (BJT) has had an unprecedented impact on the electronic industry and helped to usher in the digital revolution prominently. However, the critical part of BJT, p–n junction, is formed by carefully incorporating substitutional impurities in traditional bulk semiconductors and it is difficult to implement in nanostructured device. In this work, a floating‐base BJT device is demonstrated by growing C8‐BTBT/MAPbBr3/C8‐BTBT PNP heterostructure in liquid phase. Growth of two semiconductor microwires into a crisscross heterojunction is achieved through template‐guided printing and antisolvent crystallization method. The proof‐of‐concept phototransistor demonstrates broadband light absorption from ultraviolet (UV) to visible spectral region, which exhibits enhanced photoresponsivities of 1.28 A W–1 to UV and 0.425 A W–1 to visible light, respectively. In addition, the improved photoelectric amplification behavior of C8‐BTBT/MAPbBr3/C8‐BTBT phototransistor is observed by comparing with the performance of C8‐BTBT/MAPbBr3 two‐component photodiode. The maximal gain can reach up to ≈600 and can be maintained ≥200 at the positive bias. The device provides new attractive prospects in the investigation of integrated circuits based on micro‐structured semiconductors.

Deconvoluting the energy transport mechanisms in all-inorganic CsPb2Br5/CsPbBr3 perovskite composite systems

CsPb2Br5/CsPbBr3 composite systems have received considerable attention among numerous lead halide perovskite materials due to their significantly enhanced photoluminescence intensity and stability against moisture. However, the luminescence mechanism of CsPb2Br5 based materials remains controversial, which significantly hinders the further material design and utilization for optoelectronic devices. In this work, to deconvolute their luminescent mechanisms, high-quality CsPb2Br5 crystals without any undesired by-products and impurities have been first prepared by a microwave-assisted synthesis method. The luminescence-inactive characteristics of the material are then confirmed by the steady-state absorption, photoluminescence, transient absorption spectra, and time-resolved terahertz spectroscopy. The prepared CsPb2Br5 crystals exhibit excellent crystallinity and enhanced thermal stability, particularly that they can maintain their crystalline structures in polar organic solvents. By simply manipulating the ratios of different precursor materials, it is witnessed that the green emission comes from the CsPbBr3 adhered, nucleated, and grown on the CsPb2Br5 crystals. Ultrafast transient absorption measurements in visible and terahertz spectral regions reveal that with the help of phonon scattering-assisted hopping at interfacial states, intersystem crossing dominates the electron transfer process in the composite crystals. As a result, the CsPb2Br5 and CsPbBr3 interact extensively with each other. Meanwhile, the Auger recombination rate and the defect-related non-radiative process are suppressed in the composite crystals, thereby enhancing the fluorescence of composite crystals. This work has not only deconvoluted the controversial and unclear luminescent mechanisms of CsPb2Br5 materials but also established a pathway to design and enhance the fluorescence of materials for technological applications.

Micropattern-assisted absorption enhancement and wettability surface on ZnO via single femtosecond laser beam tailoring

Herein, we report significant micropattern-assisted absorption enhancement on crystalline ZnO fabricated by a single femtosecond laser beam (400 nm, 35 fs, kHz). This two-dimensional micropattern, which is achieved by one-step femtosecond laser tailoring, sharply contrasts the traditional laser-induced periodic surface structure. The large-area preparation of two-dimensional micropatterns can be achieved via an overlapped scanning method, showing potential practical applications. We find that the absorption shows an increasing trend, with maximum values of 90–99% in the ultraviolet spectral regions and 75–80% in the visible spectral regions. Additionally, theoretical results demonstrate that a strong electric field enhancement phenomenon exists on the two-dimensional structure from the ultraviolet to near-infrared wavelengths. We also determine the liquid contact angle of these micropattern structures, which exhibit controlled wettability characteristics that are dependent on laser energy.

Indirect excitation and luminescence activation of Tb doped indium tin oxide and its impact on the host’s optical and electrical properties

The effect of adding terbium to indium tin oxide (ITO) thin films on the electrical, optical and light emission properties was investigated. The films were prepared by radio frequency dual magnetron sputtering, maintaining a high optical transmittance in the ultraviolet and visible spectral regions, and a low electrical resistivity ranging from to . Terbium-related luminescence is achieved after annealing at 470 ∘C in air at atmospheric pressure. Electrical resistivity and optical transmittance were measured after each annealing step to evaluate the compromise between the achieved light emission intensity, electrical and optical properties. Additionally, temperature dependence of Tb-related luminescence quenching was assessed by temperature-dependent photoluminescence measurements, from 83 to 533 K, under non-resonant excitation. Thermal quenching activation energies suggest an effective energy transfer mechanism from the ITO host to the rare-earth (RE) ions. This indirect excitation mechanism was modeled using a spherical potential-well and a tight-binding one-band approximation approaches, describing a short-range charge trapping process and subsequent formation of bound excitons to RE ion clusters.

Spectroscopy of triplet-excited complexes of oxygen with spruce cone molecules extract from picea abies in AOT micelles under combined photoexcitation

The paper presents a method for obtaining an extract from the cones of Picea Abies spruce and fabrication a microemulsion based on it, which has an absorption spectrum in the UV region and luminescence in the red region (680-720 nm). A spectral study of a microemulsion with an extract containing polyphenols and phenolic acids (vanillic, protocatechuic, oxybenzoic) in the visible and IR spectral regions has been carried out. On the basis of time-resolved spectral data, the possibility of formation of reactive oxygen species, in particular, singlet oxygen, in a microemulsion under the action of UV radiation has been proved. A technique for oxygen saturation of microemulsions with an extract has been developed. The quantum efficiency of singlet oxygen generation upon absorption of light at a wavelength of 400 nm by an extract with different concentrations of molecular oxygen inside reverse micelles has been determined. It has been established that the quantum yield of singlet oxygen (1Δg) in a microemulsion with an extract can be increased by a factor of 9.5 and this value can be controlled by changing the oxygen accumulation time inside the micelle. It was found that with the oxygen concentration grow, both extract fluorescence intensity and optical density increase, and long-lived delayed fluorescence appears. A controlled concentration process of oxygen complexation with extract molecules accompanied by chemiluminescence in the red region of the spectrum has been studied. The rate constants of energy deactivation in the contact complex after photoexcitation during quenching of triplet states of the extract molecules have been determined

Origin of proton induced fluorescence quenching of colloidal carbon dots: reshaping of Schrödinger wavefunctions and huge red shift of transition energy

The fluorescence quenching by protons is a universal phenomenon but the mechanism remains unclear. Here, we take the fluorescent amide-terminated carbon dots as a prototype to study the proton fluorescence quenching mechanism by using both experiments and time-dependent density functional theory calculations. The study reveals that when an approached proton is captured by the weakly negatively charged fluorophore group of the colloidal carbon dot, it will substantially change the electron wavefunctions owing to the strong proton–electron interaction, and this leads to highly diminished energy gap and resultant fluorescence quenching in the visible spectral region. The protons generated by hydrolysis of various types of metal ions also exhibit fruitful fluorescence quenching and the quenching efficiency is roughly proportional to the hydrolysis constant of the metal ion. This fluorescence quenching mechanism is quite distinct from the conventional ones involving electron or energy transfer.

Tb,Y:SrF2 crystal for efficient laser operation in the visible spectral region.

A Tb,Y:SrF2 crystal with high optical quality is grown using the temperature gradient technique. The spectroscopic and laser properties of the crystal in the visible spectral region are studied. A fluorescence lifetime of 5.6 ms is measured from the crystal, which is beneficial for laser operation with a low threshold. A continuous-wave Tb,Y:SrF2 laser delivers an output power of 259 mW at 545 nm, with a slope efficiency of 35.2%. To the best of the authors' knowledge, this is the first report on a Tb-doped SrF2 laser and represents the highest output power for visible alkaline-earth fluoride lasers. The limitations for power scaling are discussed.

On the possible contribution of cationic oxygenated carbon chains CnO+, HCnO+, and OCnO+ (n = 4–9) to the diffuse interstellar bands

ABSTRACT Only four of the diffuse interstellar bands (DIBs) are currently accounted for, ascribed to electronic transitions of C$_{60}^+$. Investigations into carriers of other DIBs historically focus on charged and neutral hydrocarbons, and little information is available regarding oxygenated carbon and hydrocarbon species that result from the two most abundant heavy elements in the interstellar medium, C and O. In this study, we assess whether CnO+, HCnO+, and OCnO+ (n = 4–9) cations are viable candidates to account for DIBs using both density-functional theory (DFT) and coupled cluster single-double and perturbative triple theory, CCSD(T). For these species, the linear structures are the most stable isomers with the lowest dissociation threshold corresponding to CO loss. Optical absorptions of the oxygenated carbon chain cations are characterized by calculated vertical excitation wavelengths and their corresponding oscillator strengths using the equation-of-motion CCSD (EOM-CCSD) method. Aside from HC4O+ and HC2n +1O+, all of the species considered in this study have calculated electronic transitions that lie in the visible or near-infrared spectral regions. Minimal column densities necessary for these cations to account for DIBs have been estimated. Based on present results and the known column densities for neutral oxygenated carbon chains in TMC-1, the growth rate of charged O-bearing carbon chains via ion-neutral reaction mechanisms is judged to be too low to form a sufficient population to give rise to DIBs.

New Medium Bandgap Donor D-A1 -D-A2 Type Copolymers Based on Anthra[1,2-b: 4,3-b":6,7-c"'] Trithiophene-8,12-dione Groups for High-Efficient Non-Fullerene Polymer Solar Cells.

A new acceptor unit anthra[1,2-b: 4,3-b': 6,7-c'']trithiophene-8,12-dione (А3Т) (A2) is synthesized and used to design D-A1 -D-A2 medium bandgap donor copolymers with same thiophene (D) and A2 units but different A1, i.e., fluorinated benzothiadiazole (F-BTz) and benzothiadiazole (BTz) denoted as P130 and P131, respectively. Their detailed optical and electrochemical properties are examined. The copolymers show good solubility in common organic solvents, broad absorption in the visible spectral region from 300 to 700 nm, and deeper HOMO levels of -5.45 and -5.34 eV for P130 and P131, respectively. Finally, an optimized polymer solar cell (PSC) based on P131 as the donor and narrow bandgap non-fullerene small molecule acceptor Y6 demonstrated a power conversion efficiency (PCE) of >11.13%. To further improve the efficiency of the non-fullerene PSC, the P130 is optimized by introducing a fluorine atom into the BTz unit, F-BTz acceptor unit, and PCE PSC based on P130: Y6 active layer increased to >15.28%, which is higher than that for the non-fluorinated analog P131:Y6. The increase in the PCE for former PSC is attributed to the more crystalline nature and compact π-π stacking distance, leading to more balanced charge transport and reduced charge recombination. These remarkable results demonstrate that A3T-based copolymer P130 with F-BTz as the second acceptor is a promising donor material for high-performance PSCs.

Wide-angle broadband antireflection coatings based on boomerang-like alumina nanostructures in visible region

A novel boomerang-like alumina based antireflective coating with ultra-low reflectance has been produced for light incidence angles form 0 up to 45°. Boomerang-like alumina nanostructures have been fabricated on the BK7 glass substrates by dip-coating and surface modification via hot water treatment. To achieve the lowest residual reflectance, the effect of dip-coating rate and hot-water temperature in the treatment process has been investigated and optimized. To further investigate the boomerang-like alumina nanostructure and extract its graded refractive index profile by fitting the measured reflectance spectrum with the simulated one, a simulation based on the finite-difference time-domain (FDTD) method has been performed. The average reflectance measured at normal incidence for double-sided coated BK7 glass substrates is only 0.3% in the visible spectral region. Considering both sides, the average reflectance of the substrate decreased in the spectral range of 400–700 nm down to 0.4% at incidence angles of 45° by applying the boomerang-like alumina antireflection coatings. The optimized single layer boomerang-like alumina coating on the curved aspheric lens exhibited a low average reflectance of less than 0.14% and an average transmittance of above 99.3% at normal incidence. The presented process is a simple and cost-effective route towards broadband and omnidirectional antireflection coatings, which have promising potential to be applied on substrates having large scales with complex geometric shapes.

Towards Power Scaling of Simple CW Ultraviolet via Pr: LiYF4-LBO Laser at 320 nm

Intracavity frequency doubling of diode-pumped continuous-wave Pr^3+ laser in visible spectral region is a highly efficent and cost-effective method for the generation of high-performance continuous-wave ultraviolet laser. However, to date, diode-pumped continuous-wave frequency doubled Pr^3+-based ultraviolet laser has still been power limited only to about one watt. In this work, employing two 12-W blue diode lasers as pump sources individually, we achieved maximum output powers up to 1.82 W and 1.73 W of ultraviolet lasers at about 320 nm by intracavity frequency doubling of continuous-wave Pr:LiYF₄ (YLF) lasers at 640 nm. The used nonlinear frequency doubler is a 12-mm LBO crystal. For further power scaling of the ultraviolet laser, a total pump power of 24 W was injected into the laser crystal by configuring a double end pumping geometry. Under this situation, a maximum output power of 3.22 W can be achieved, which is believed to be the highest continuous-wave ultraviolet laser via intracavity frequency doubling. This solid-state 320-nm ultraviolet laser could replace the relatively cumbersome He-Cd vapor laser for a variety of applications.

Photophysics and Electrochemistry of Biomimetic Pyranoflavyliums: What Can Bioinspiration from Red Wines Offer?

Natural dyes and pigments offer incomparable diversity of structures and functionalities, making them an excellent source of inspiration for the design and development of synthetic chromophores with a myriad of emerging properties. Formed during maturation of red wines, pyranoanthocyanins are electron-deficient cationic pyranoflavylium dyes with broad absorption in the visible spectral region and pronounced chemical and photostability. Herein, we survey the optical and electrochemical properties of synthetic pyranoflavylium dyes functionalized with different electron-donating and electron-withdrawing groups, which vary their reduction potentials over a range of about 400 mV. Despite their highly electron-deficient cores, the exploration of pyranoflavyliums as photosensitizers has been limited to the “classical” n-type dye-sensitized solar cells (DSSCs) where they act as electron donors. In light of their electrochemical and spectroscopic properties, however, these biomimetic synthetic dyes should prove to be immensely beneficial as chromophores in p-type DSSCs, where their ability to act as photooxidants, along with their pronounced photostability, can benefit key advances in solar-energy science and engineering.

Fabrication, Characterization and Annealing of Linear Variable Optical Filter in Visible Spectral Region

Fabrication, Characterization and Annealing of Linear Variable Optical Filter in Visible Spectral Region