Red Wavelength Region Research Articles

Photosystem I enhanced perovskite–Organic tandem solar cell efficiency

Tandem solar cells (TSC) have been introduced to better absorb the spectrum of sunlight and reduce optical loss. Among these, perovskite–organic tandem solar cells (P-OTSC) have emerged as a prominent topic over the last decade due to their complementary absorption spectrum. Additionally, incorporating diverse pigmented protein complexes in TSC fabrication is becoming more common. Natural chlorophyll-containing photosystems have garnered significant attention for their naturally solar-tuned absorption spectra. Photosystem I protein (PSI), is the most robust component of oxygenic photosynthesis and contains over 100 Chl a molecules/complex with two sharp absorbance peaks at 430 and 665 nm. PSI offers a second and complementary active layer because P-OTSCs often have a low extinction coefficient in the red wavelength region. In this research, the performance of P-OTSCs was enhanced by improving the absorption spectrum by utilizing an isolated plant PSI complex. The circuit current density (Jsc) increased from 14.23 mA/cm² to 14.95 mA/cm², and the power conversion efficiency (PCE) of P-OTSCs increased from 19.32 % to 20.24 %. We also observed that the external quantum efficiency (EQE) shows an apparent increase in the long wavelength region, reflecting the absorbance of light by PSI. This work is the first to report the integration of PSI into perovskite–organic tandem solar cells, and it motivates new design considerations that can further boost efficiency and utilize natural, earth-abundant pigment proteins.

Up-converted white light emission in Er3+ doped MgAl2O4 nanocrystals

This work presents the influence of host defect centers on the photoluminescence characteristics of Mg1−xErxAl2O4 (x = 0.005, 0.01, and 0.03) nanocrystals under UV and near-infrared (NIR) excitations. The spinel-structured nanocrystals are synthesized through the combustion method. The Rietveld refinement and nuclear magnetic resonance analyses estimated the Er3+ ion occupancy at octahedral and other random sites of the MgAl2O4 lattice, and the existence of various lattice defects. Diffuse reflectance spectra showed broad bands attributed to oxygen vacancies as well as antisite defects and sharp peaks attributed to f–f transitions of Er3+ ions. The upconversion luminescence spectra consisted of sharp emission lines, ascribed to Er3+ ions, in the green and red wavelength regions, which overlapped over the broad curve attributed to intrinsic defects. Further, the UV excited downconversion luminescence spectra showed two broad emission bands in blue–violet and red-NIR regions with a very weak Er3+ ion emission feature. This up- and downconversion emission revealed energy transfer between host and Er3+ ions via intrinsic defects. As a result, the emission color changes from bluish purple to white by varying the excitation wavelength from UV to NIR. This rare earth activated luminescence from MgAl2O4 nanocrystals would exhibit potential applications in display devices and solid-state lighting.

Morphology and spectral sensitivity of long visual fibers and lamina monopolar cells in the butterfly Papilio xuthus.

Extensive analysis of the flower-visiting behavior of a butterfly,Papilio xuthus, has indicated complex interaction between chromatic, achromatic, and motion cues. Their eyes are spectrally rich with six classes of photoreceptors, respectively sensitive in the ultraviolet, violet, blue, green, red, and broad-band wavelength regions. Here, we studied the anatomy and physiology of photoreceptors and second-order neurons ofP. xuthus, focusing on their spectral sensitivities and projection terminals to address where the early visual integration takes place. We thus found the ultraviolet, violet, and blue photoreceptors and all second-order neurons terminate in the distal region of the second optic ganglion, the medulla. We identified five types of second-order neurons based on the arborization in the first optic ganglion, the lamina, and the shape of the medulla terminals. Their spectral sensitivity is independent of the morphological types but reflects the combination of pre-synaptic photoreceptors. The results indicate that the distal medulla is the most plausible region for early visual integration.

NGHIÊN CỨU CHẾ TẠO MÔ ĐUN CHUYỂN HƯỚNG BỨC XẠ LASER BÁN DẪN GHÉP SỢI QUANG 650 NM ỨNG DỤNG TRONG QUANG TRỊ LIỆU VÀ QUANG SINH DIỆT KHUẨN

Currently, diode lasers in the red wavelength region, especially at 650 nm, are extensively utilized in phototherapy and photodynamic inactivation of bacterials by numerous research groups in the field of lasers for biomedical application. These devices offer exceptional advantages, such as their compact size, ease of design and integration, user-friendliness, and high safety for both operators and patients. Among these, fiber-coupled diode lasers provide an efficient solution for delivering radiation from the laser chip to the desired location. However, further optimization is still required for the fabrication technological development of these devices to meet specific application needs. This includes aspects like reducing manufacturing costs, improving component usability during operation, and meeting specialized usage requirements. To develop the technology for device fabrication, addressing the aforementioned demands, we conducted research on the design, fabrication, and characterization of fiber-coupled semiconductor lasers operating at a wavelength of 650 nm. The characterization results demonstrate that the manufactured devices can operate at maximal pumping current of 100 mA and under varying temperatures from 25oC to 40oC. Additionally, a radiation output orientation module has been designed and integrated at the end of the optical fiber to meet various demands in phototherapy and photodynamic inactivation of bacterials.

L-Arginine-Functionalized Carbon Dots with Enhanced Red Emission and Upregulated Intracellular L-Arginine Intake for Obesity Inhibition.

Obesity is a major global health problem that significantly increases the risk of many other diseases. Herein, a facile method of suppressing lipogenesis and obesity using L-arginine-functionalized carbon dots (L-Arg@CDots) is reported. The prepared CDots with a negative surface charge form stronger bonds than D-arginine and lysine with L-Arg in water. The L-Arg@CDots in the aqueous solution offer a high photoluminescence quantum yield of 23.6% in the red wavelength region. The proposed L-Arg functionalization strategy not only protects the red emission of the CDots from quenching by water molecules but also enhances the intracellular uptake of L-Arg to reduce lipogenesis. Injection of L-Arg@CDots can reduce the body weight increase in ob/ob mice by suppressing their food intake and shrinking the white adipose tissue cells, thereby significantly inhibiting obesity.

Preparation of Ag–Fe2O3-Based black and electrically insulating coatings by magnetron sputtering from metal targets

Black and electrically insulating coatings provide touch panel displays with a classic appearance. In this study, black and electrically insulating Ag–Fe2O3-based coatings were prepared using reactive magnetron sputtering, stainless steel and silver foil. The thin films prepared with oxygen introduction and no Ag foil showed blue light absorption and high electrical resistance, which are comparable to those of Fe2O3 single crystals. The optimal Ag foil size for maintaining a high electrical resistivity of 108 Ω·sq−1 was determined to be 54 mol%Ag in the film samples. Black and electrically insulating thin films composed of metallic Ag, amorphous Ag–Fe–O, and slightly crystallized Fe2O3 were prepared using 3.4 or 3.9 %O2. Metallic Ag segregated randomly in the high-refractive-index Fe2O3-based matrix, resulting in plasmonic absorption over a wide range of wavelengths centered in the red-wavelength region. At 3.9 %O2, a high sheet resistance of 108 Ω·sq−1 and strong visible absorption of 35.2 μm−1 (on average), slightly deviating by 2.4 μm−1 were simultaneously achieved by clear phase separation of the Ag grains and Fe2O3-based matrix. A clear phase separation mechanism based on thermodynamic nonequilibrium oxidation of the metallic Ag phase is proposed.

A study on the optical properties of a novel flower-core photonic crystal fiber infiltrated with CCl4

A novel design of photonic crystal fiber with a flower-core is proposed for the first time to optimize dispersion suitable for broadband supercontinuum generation. The numerical simulation of the propagation of light modes in optical fibers is computed by solving Maxwell's wave equations with the full-vector finite-difference eigenmode method. As a result, near-zero ultra-flat all-normal and anomalous dispersion was achieved with fluctuations of ±0.978 ps/nm.km in the 294 nm wavelength region and ±1.168 ps/nm.km in the 432 nm wavelength region, respectively. Furthermore, the dispersion value at the pump wavelength is about 10 times lower than in previous papers. The combination of CCl4 infiltration into the hollow core and the air hole's size heterogeneity in the cladding also enhances the nonlinear properties of the fibers. The effective mode areas less than 2 µm2 at the pump wavelength can help the supercontinuum spectrum to broaden further towards the red wavelength region. Three fibers with structural parameters Ʌ = 0.8 µm, d1/Ʌ = 0.45, Ʌ = 0.9 µm, d1/Ʌ = 0.5, and Ʌ = 0.9 µm, d1/Ʌ = 0.45 are proposed for supercontinuum generation with low peak power due to the nonlinear coefficients as high as hundreds W−1.km−1. These fibers are a new class of optical fibers, highly efficient laser sources that replace traditional glass-core optical fibers.

Space debris spectroscopy: Specular reflections at LEO regime

Space debris, the dysfunctional human-made objects on Low Earth Orbits (LEO), occasionally irradiate bright specular flares or glints which can be detected by a ground-observer. These events are reflections of sunlight from flat, highly reflective surface elements and their spectra represent the ability of the material to reflect sunlight in specific regions of wavelengths. Spectral features then define satellite’s exterior properties, mainly the colour of the surface material. Presented here are the reduction techniques and reflectance spectra of LEO space debris acquired by slit-less spectral cameras AMOS-Spec–HR. Cameras are a part of world-wide distributed network All-sky Meteor Orbit System(AMOS), designed for meteor observation, and operated by the Comenius University in Bratislava. During spectroscopic observations from 2016 to 2021, AMOS-Spec–HR harnessed numerous debris recordings and by data mining of its archives, dozens of spectra of flares and glints were retrieved. According to their properties, reflectance spectra can be organized into distinct categories: Category I – Convex Spectra (includes spectra of solar panels), Category II – Spectra Increasing towards Red Wavelength Region (common for spectra of golden polyimide Kapton foil, the surface material of Multi-Layer Insulation), and Category III – Flat, Straight-lined Spectra (typically includes spectra of aluminium, or other silvery alloys and metals). Defined spectral types were confronted and correlated with laboratory spectra of reflective aerospace materials obtained from literature.

HOTOVOLTAIC PROPERTIES OF FUNCTIONALIZED INDODICARBOCYANINE DYE

The effect of the chemical structure of polymethine dyes on their spectral-luminescent and photovoltaic properties has been studied. It has been shown that the introduction of hydroxyl functional groups into the dye structure leads to a bathochromic shift of the absorption and fluorescence bands. During the adsorption of dyes on the surface of titanium dioxide, a shift of their spectra to the red wavelength region was recorded with a simultaneous broadening of the bands caused by dye aggregation on the semiconductor surface. A decrease in the lifetimes of the excited state of molecules by 64 and 30% was registered for dyes 1 and 2, respectively. Quenching of the fluorescence lifetimes of adsorbed molecules is the result of electron transfer from the dye to the semiconductor. Measurements of the photovoltaic parameters of the studied dye-sensitized solar cells showed a higher efficiency for the functionalized dye, which is associated with better adsorption of this compound on TiO2

Estimating grassland vegetation cover with remote sensing: A comparison between Landsat-8, Sentinel-2 and PlanetScope imagery

Grassland fractional vegetation cover (FVC) accurate mapping on a large scale is crucial, since degraded grasslands contribute less to provisioning services, carbon storage, water purification, erosion control and biodiversity conservation. The spatial and temporal resolution of Sentinel-2 (S2) and PlanetScope (PS) data has never been explored for grassland FVC estimation so far and will enable researchers and agencies to quantify and map timelier and more precisely grassland processes. In this paper we compare FVC estimation models developed from Landsat-8 (L8), S2 and PS imagery. The reference grassland FVC dataset was obtained on the Paganella ski runs (46.15°N, 11.01°E, Italy) applying unsupervised classification to nadir grassland RGB photographs taken from 1.35 m above the soil. Fractional Response Models between reference FVC and 18 vegetation indices (VIs) extracted from satellite imagery were fitted and analysed. Then, leave-one-out cross validation and spatiotemporal change analysis were also performed. Our study confirms the robustness of the commonly used VIs based on the difference between NIR and the red wavelength region (R2 = 0.91 for EVI using S2 imagery) and indicate that VIs based on the red-edge spectral region are the best performing for PS imagery (R2 = 0.89 for RECI). Only medium to high spatial resolution imagery (S2 and PS) precisely mapped spatial patterns at the study site, since grasslands FVC varies at a fine scale. Previously available imagery at medium to low spatial and temporal resolution (e.g., L8) may still be interesting for analysis requiring long time-series of data.

Multi-conformational Luminescence and Phosphorescence of Few Phenazine 1,2,3-triazole Molecules.

Dropcast films produced from blends solutions of phenazine 1,2,3-triazole molecules in very lowconcentrations in a 1,3-Bis (N-carbazolyl) benzene (mCP) matrix were investigated at room tem-perature. The mCP acts as an optically inert matrix, having no influence on the emission propertiesof the guest molecules. Its conductive properties ensure the blend films as completely organic active layers. The fluorescent and phosphorescent emissions of the guest molecules in blue, green, red and also in white are relatively intense, without the need to mix different organic materials. The excitation of the system occurs directly by the incident laser beam on the films. The steady-state spectroscopy for the blue monomer and green dimer singlet fluorescence emissions were investigated. The analysis of their temporal decays was done using a different approach based on the Exponentially Modified Gaussian function. The phosphorescent emissions of the triplet steady-states, in the orange or in the red wavelength regions, were observed to be correlated, respectively, to the formation of guest monomers or to the guest dimers singlet states.

Lutidine derivatives for live-cell imaging of the mitochondria and endoplasmic reticulum.

The mitochondria and endoplasmic reticulum (ER) are highly dynamic subcellular structures essential for several biological functions. The development of non-toxic, wash-free fluorophores to visualize these structures inside cells aid in understanding their localization and dynamics in diverse cellular processes. In this paper, we report the synthesis and characterization of lutidine-based cationic fluorophores bearing push-pull substituents exhibiting emission in green and red wavelength regions and their subcellular localization in living cells. The confocal imaging of the molecules in a cellular domain reveals the robust localization of three molecules (2, 4 and 5) in the mitochondria and two molecules with polyfluorophenyl substituents (6 and 7) in the ER. At the same time, the other two molecules (1 and 3) showed non-specific imaging. These molecules can also be used to sense the altered viscosity of the stressed ER and investigate its dynamics.

Design and fabrication of multilayer dichroic beam splitter

Beam splitters are primarily used for applications like avionic displays, optical storage, fluorescence applications, optical interferometry, semiconductor instrumentation where some of the information needs to be reflected as well as transmitted. They operate on the principle of light being reflected and transmitted by various interfaces where it is split by percentage of overall intensity or wavelength. In this study, design and fabrication of a dichroic optical beam splitter for filtering of red and green light from a white light source has been presented. Here, a symmetric dielectric multilayer stack with 15 alternating layers of alumina and silica are deposited on BK-7 glass using e-beam evaporation technique. High and low refractive indices of 1.63 and 1.46 respectively are used with quarter-wave optical thicknesses of layers. The beam splitter is designed for 45 ̊ angle of incidence using FilmstarTM design software. Transmission spectrum obtained from UV-Vis-NIR double beam spectrophotometer shows reflectance of ~54% at 660 nm (red wavelength region) and transmittance of ~88% at 550 nm (green wavelength region). The coated sample is further subjected to adhesion and hardness test according to MIL standard and no peel off or scratch is observed indicating excellent durability of the coating. The modelled and measured results closely agree with one another over visible spectral regions. Copyright © 2017 VBRI Press.

Enhanced performance of GaN-based visible flip-chip mini-LEDs with highly reflective full-angle distributed Bragg reflectors

High-efficiency GaN-based visible flip-chip miniaturized-light emitting diodes (FC mini-LEDs) are desirable for developing white LED-backlit liquid crystal displays. Here, we propose a full-angle Ti3O5/SiO2 distributed Bragg reflector (DBR) for blue and green FC mini-LEDs to enhance the device performance. The proposed full-angle Ti3O5/SiO2 DBR is composed of different single-DBR stacks optimized for central wavelength in blue, green, and red light wavelength regions, resulting in wider reflective bandwidth and less angular dependence. Furthermore, we demonstrate two types of GaN-based FC mini-LEDs with indium-tin oxide (ITO)/DBR and Ag/TiW p-type ohmic contacts. Experimental results exhibit that the reflectivity of full-angle DBR is higher than that of Ag/TiW in the light wavelength range of 420 to 580 nm as the incident angle of light increases from 0° to 60°. As a result, the light output powers (LOPs) of blue and green FC mini-LEDs with ITO/DBR are enhanced by 7.7% and 7.3% in comparison to blue and green FC mini-LEDs with Ag/TiW under an injection current of 10 mA. In addition, compared with FC mini-LED with Ag/TiW, light intensity of FC mini-LED with ITO/DBR is improved in side direction, which is beneficial to mix light in backlight system of liquid crystal displays (LCDs).

Optical Bend Sensor Based on Eccentrically Micro-Structured Multimode Polymer Optical Fibers

We report on a novel bend sensor with high flexibility and elasticity based on Bragg grating structures in polymer optical fibers to detect bending for the measurement of movement. The concept is very simple and relies on the inscription of eccentrical Bragg gratings into multimode graded-index polymer optical fibers via contact exposure with a krypton fluoride excimer laser in the ultraviolet region and an optimized phase mask. Depending on the fiber deformation, the lattice constant of the inscribed Bragg grating is strained or compressed due to its position relative to the fiber core. This in turn results in a specific shift of the Bragg wavelength of up to $1.3\text{ nm}$ to the red or blue wavelength region, respectively, which is sufficiently large to be reliably detected. Therefore, as proof of principle, deformation along one axis can be observed with a single Bragg grating with a maximum sensitivity of up to $65\text{ pm/m}^{-1}$ . Moreover, multiple Bragg gratings inscribed into the same polymer optical fiber at different positions around the fiber axis allow to determine the shape deformation of the fiber relative to a reference frame with similar accuracy. Consequently, this technology could form the basis for new applications in the areas of medical diagnostics, robotics or augmented reality, which are lacking affordable sensor systems to date.

Synthesis and Photophysical Properties of Light-Harvesting Gold Nanoclusters Fully Functionalized with Antenna Chromophores.

The development of efficient light-harvesting systems is important to understand the key aspects of solar-energy conversion processes and to utilize them in various photonic applications. Here, atomically well-defined gold nanoclusters are reported as a new platform to fabricate artificial light-harvesting systems. An efficient amide coupling method is developed to synthesize water-soluble Au22 clusters fully protected with pyrene chromophores by taking advantage of their facile phase-transfer reaction. The synthesized Au22 clusters with densely packed 18 pyrene chromophores (Au22 -PyB18 ) exhibit triple-emission in blue, green, and red wavelength regions arising respectively from pyrene monomer, pyrene excimer, and Au22 emission, producing bright white light emission together. The photoluminescence of Au22 is enhanced by more than tenfold, demonstrating that pyrenes at the periphery efficiently channel the absorbed energy to the luminescent Au22 at the center. A combination of femtosecond transient absorption and anisotropy measurements of Au22 -PyB18 explicitly reveals three main decay components of 220 fs, 3.5ps, and 160ps that can be assigned to energy migration between pyrenes and energy transfer processes from pyrene monomer and excimer to the central Au22 , respectively.

Coral-spawn slicks: Reflectance spectra and detection using optical satellite data

This study provides the first report of reflectance spectra of coral-spawn slicks and their detection using optical satellite data. The reflectance spectra show that coral-spawn slicks can be discriminated from other sea-surface features such as wave foam and floating Sargassum. Analysis of Planet Dove and Sentinel-2B imagery allowed successful detection of coral-spawn slicks at Ishigaki Island, Okinawa, Japan (24°31′40″N, 124°17′31″E), by using reflectance values in the green and red wavelength regions. This detection was attributable to both their high spatial resolution (3.7 m and 10 m, respectively) and high temporal resolution (1 day and 5 days, respectively), given that coral spawning occurs within a short period (up to several days), typically once a year, and that the coral-spawn slicks have narrow widths of ~10 m. The number of the detected coral-spawn slicks was small, possibly because of coral decline around Ishigaki Island caused by the 2016 worldwide mass coral bleaching event. High-frequency satellite observations, including those from satellite constellations, should provide a powerful tool for understanding coral-reef processes and features whose detection requires high spatial and temporal resolution.

Bi3+ and Eu3+ Activated Luminescent Behaviors in Non-Stoichiometric LaO0.65F1.7 Structure.

Optical materials composed of La1-p-qBipEuqO0.65F1.7 (p = 0.001–0.05, q = 0–0.1) were prepared via a solid-state reaction using La(Bi,Eu)2O3 and NH4F precursors at 1050 °C for two hours. X-ray diffraction patterns of the phosphors were obtained permitting the calculation of unit-cell parameters. The two La3+ cation sites were clearly distinguished by exploiting the photoluminescence excitation and emission spectra through Bi3+ and Eu3+ transitions in the non-stoichiometric host lattice. Energy transfer from Bi3+ to Eu3+ upon excitation with 286 nm radiation and its mechanism in the Bi3+- and Eu3+-doped host structures is discussed. The desired Commission Internationale de l’Eclairage values, including emissions in blue-green, white, and red wavelength regions, were obtained from the Bi3+- and Eu3+-doped LaO0.65F1.7 phosphors.

Synthesis and characterization of GaPN/GaP heterostructures grown on silicon (001)

III-V compound semiconductor heterostructures grown on Si wafers are one of the promising materials in modern optoelectronics. The most promising candidate providing lattice matching with Si is III-phosphide-based alloys diluted with nitrogen. In this work, we study the effect of growth conditions on the structure and optical properties of GaP1−xNx/GaP/Si planar heterostructures synthesized by plasma assisted molecular beam epitaxy. A series of samples with a maximum impurity nitrogen content as high as 5.05% was synthesized. The morphological, structural and optical properties of heterostructures are studied with scanning electron microscopy and optical spectroscopy. All of the samples demonstrate a broad photoluminescence (PL) response in the red wavelength region at room temperature (RT). The most efficient RT PL is obtained with the samples grown under a high nitrogen gas flow through a nitrogen plasma cell.

Oxygen-Sensing Probes and Bandage for Optical Detection of Inflammation.

Small-molecular and macromolecular optical probes based on an iridium complex chromophore were designed for detecting hypoxic inflammation in this work. The optical probes had a large conjugated ligand that could extend its phosphorescence emission to the red-wavelength region, thus increasing the tissue penetration depth of the optical signal. Due to good water solubility, the macromolecular optical probe could image both monolayer cells and three-dimensional multicellular spheroids. Moreover, this macromolecular probe was able to effectively image inflammation and distinguish healthy and inflammatory regions in a mouse model of lipopolysaccharide (LPS)-induced inflammation with low background interference. Furthermore, we integrated the hydrophobic small-molecular probe into the polyurethane thin film, and the resulting film successfully monitored the inflammation of chronic wounds in a mouse model. This work demonstrated the great potential of the iridium complex in optical imaging hypoxia and hypoxia-associated inflammation and will have significant impact on the design of high-sensitivity sensors for the detection of hypoxia.