Transmittance In Visible Range Research Articles

Thermochromic Nanocellulose Films for Temperature-Adaptive Passive Cooling.

Energy efficiency in habitation spaces is a pivotal topic for maintaining energy sufficiency, cutting climate impact, and facilitating economic savings; thus, there is a critical need for solutions aimed at tackling this problem. One viable approach involves complementing active cooling methods with powerless or passive cooling ones. Moreover, considerable scope remains for the development of passive radiative cooling solutions based on sustainable materials. Cellulose, characterized by its abundance, renewability, and biodegradability, emerges as a promising material for this purpose due to its notable radiative cooling potential exploiting the mid-infrared (MIR) atmospheric transmission window (8-13 μm). In this work, we propose the utilization of thermochromic (TC) materials in conjunction with cellulose nanofibrils (CNF) to confer temperature-dependent adaptivity to hybrid CNF films. We employ a concept where high reflection, coupled with MIR emission in the heated state, facilitates cooling, while high visible light absorption in the cold state allows heating, thus enabling adaptive thermal regulation. CNF films were doped with black-to-leuco TC particles, and a thin silver layer was optionally applied to the films. The films exhibited a rapid transition (within 1 s) in their optical properties at ∼22 °C, becoming transparent above the transition temperature. Visible range transmittance of all samples ranged from 60 to 90%, with pronounced absorption in the 8-13 μm range. The cooling potential of the films was measured at 1-4 °C without any Ag layer and ∼10 °C with a Ag layer. In outdoor field testing, a peak cooling value of 12 °C was achieved during bright sunshine, which is comparable to a commercial solar film. A simulation model was also built based on the experimental results. The concept presented in this study extends beyond applications as standalone films but has applicability also in glass coatings. Overall, this work opens the door for a novel application opportunity for green cellulose-based materials.

Preparation and properties of 5 at.% Er3+: SrF2 transparent ceramics by cold sintering

SrF2 transparent ceramics are frequently utilized as gain materials for solid-state lasers because of their excellent optical properties. In this paper, 5 at.% Er3+: SrF2 nanoparticles were synthesized by chemical coprecipination method, and 5 at.% Er3+: SrF2 transparent ceramics were prepared in one step by cold sintering process, and their microstructure and optical properties were studied. The results indicate that Er3+:SrF2 transparent ceramics prepared at 300 °C and 468 MPa exhibit a dense structure, uniform particle size, and excellent transmittance. The average visible range transmittance of the sample is 48.59%, while the transmittance at 1100 nm reaches up to 76.94%. Moreover, this sintering process requires a temperature that is lower by as much as 500 °C compared to traditional methods. In addition, green emission (about 540 nm) and red emission (about 660 nm) of 2H11/2、4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions were observed in the visible range of the 375 nm laser excitation. It provides a novel and green idea for the preparation of Er: SrF2 transparent ceramics at ultra-low temperature.

Morphological and optical properties of Nb-doped ZnO nanoparticles

Niobium (Nb) was successfully doped into zinc oxide (ZnO) thin film via a modified sol–gel spin coating technique. Zinc acetate, diethanolamine, and isopropyl were used as starting material, stabilizer, and solvent, respectively. Energy Dispersive X-ray Spectroscopy (EDX) analysis shows the presence of Niobium of 1.01 at. %. on ZnO thin films. Field Emission Scanning Electron Microscopy (FESEM) shows the thin film composed of nanoparticles. The estimation size of particles slightly reduced from 44.15 nm for undoped ZnO nanoparticles to 35.77 nm after the introduction of the niobium dopant. The roughness of Nb-doped ZnO thin films was lower as compared to undoped films based on atomic force microscopy (AFM) analysis. The optical properties were investigated using UV–vis and the results had shown that both samples exhibit good transmittance in visible range. In addition, the absorption edge was red-shifted after being doped with niobium. The estimated optical band gap of Nb-doped ZnO reduced to 3.27 eV from 3.30 eV for undoped ZnO nanoparticles.

Parametric study of anti-resonant fiber designs with nesting elements for ultra-low loss over visible band

Multi-parameter design optimization is carried out to achieve low loss, wideband and single mode operation in an optical fiber for the application of single photon transmission in visible range. The fiber design is based on anti-resonant hollow core fiber without and with nesting elements. Single and dual nested rings in anti-resonant fiber are found to have significantly reduced confinement loss by a factor of 102–105 as compared to without nesting elements. Dual-ring nested design shows the best results with the low loss of the order of 10−5 dB/km in 600–700 nm. The extinction ratio of higher order modes is also higher in case of dual ring, which ensures the single mode operation in the fiber. The chromatic dispersion characteristics are also studied for the applicability of these fibers in transmission systems.

Two-Dimensional V2O5 Inverse Opal: Fabrication and Electrochromic Application.

The open-layered structure of Vanadium pentoxide (V2O5) has triggered significant interest in exploring its energy-related application as lithium (Li) intercalation cathode material. Various methods are extensively studied to improve the Li diffusion using thin films or nanoarchitecture. In this work, high-quality two-dimensional (2D) inverse opal α-V2O5 films were synthesized via a modified ‘dynamic hard template’ infiltration strategy using sacrificial polystyrene spheres (PS, a diameter of 530 nm) photonic crystal as a template. The new material exhibited an excellent porous array with featured structural colors in a large area. The electrochromic behavior was explored by combining bandgap and electrochemical characterization. On the one hand, the intercalation/deintercalation of Li+ played an important role in the bandgap (Eg), and thereafter on the visible range transmittance through changing the film’s stoichiometry and the valence of vanadium ions. On the other hand, the asymmetry of the lattice due to the disordered distribution of Li+ within the V2O5 interlayer and/or the formation of an irreversible phase explained the change in transmittance with voltage.

Self‐Assembled Woven Ag‐Nanowire 3D Network Film for Ultrathin, Transparent, and Flexible Surface Electromagnetic Interference Shielding

AbstractA kind of pollution known as electromagnetic interference (EMI), which results from ubiquitous usage of various electronic communication and military radar equipment, has received increasing attention recently. However, it is still a big challenge to obtain good EMI shielding in transparent and/or curved surfaces. In this paper, a light, ultrathin, transparent, and flexible EMI shielding film based on woven silver nanowire (Ag‐NW) 3D networks is successfully prepared via a room‐temperature template production method. For transparent application scenario, Ag‐NWs with 91% transmittance in visible range show ≈27 dB shielding efficiency. This sample shows ≈27 dB shielding efficiency, although with a low density of Ag‐NWs (≈0.0168 mg cm−2), which implies that this material has a cost‐effectiveness. Moreover, total shielding as high as ≈40 dB is obtained by using thickened Ag‐NW grids. The EMI has not changed remarkedly after bended 1200 times, which indicates the as‐prepared flexible film has a relative stability of the EMI performance. Considering the facile production technology, this material can be readily applied in transparent EMI shielding.

Effect of GZO cap-layer thickness and post-annealing treatment on GZO/HGZO bi-layer films

Hydrogen and Ga-codoped ZnO (HGZO) films caped with different thickness of Ga-doped ZnO (GZO) films (0–80 nm) were prepared by RF magnetron sputtering at room temperature, and the influences of GZO layer thickness and post-annealing treatment on structural, electrical and optical properties of the GZO/HGZO bi-layer films were investigated. The results show that increasing GZO layer thickness weakens the (002) preferred orientation, decreases the crystallize size and increases compressive stress of the films. The electrically conductive properties of the films first enhance and then degrade with increase of GZO layer thickness, and the best conductive properties can be obtained at GZO layer thickness of 20 nm. As GZO layer thickness increases, transmittance in visible range (TVis) and bandgap (Eg) of the films show a decreased trend, but their Urbach energy (Eu) increases. The crystallite size of the films first greatly and then slightly increases with increasing annealing temperatures to 400 °C, and annealing atmosphere (air or vacuum) and time (10 min or 2 h) have little effect on the crystallite size at the same annealing temperature. With increasing annealing temperature, compressive stress greatly decreases firstly and then slightly decreases under vacuum annealing or converts to tensile stress under air annealing. The conductive properties of the films degrade after vacuum annealing for 2 h, but they degrade significantly even after air annealing for 10 min. Increasing GZO layer thickness can retard the decline of conductive properties of the films under vacuum annealing of 200–400 °C for 2 h or air annealing of 200–300 °C for 10 min. With increasing annealing temperature, the TVis of the films basically shows a trend of first increase and then decrease, and the Eg and Eu of the films basically decrease. After annealing at 400 °C, the decreased Eg and Eu values of films under air annealing are close for different annealing time, but they are larger than those under vacuum annealing. Basically, thicker GZO layer is more likely to restrain the decrease of Eg, but leads to obvious decrease of Eu. In addition, effect of hydrogen doping and out-diffusion, crystallize growth and stress relaxation mechanism under annealing, and carrier transport and Eg shift mechanisms are also discussed.

Investigations the structural, optical and photovoltaic properties of La doped TiO2 photoanode based dye sensitized solar cells

Films of TiO 2 , La-doped TiO 2 (La–TiO 2 ), La–TiO 2 /TiO 2 and TiO 2 /La–TiO 2 are prepared by sol-gel (dip coating) route. The structural properties like phase, grain size, dislocation line density, inter-planner distance, and lattice parameters are calculated by X-ray diffractometer (XRD). All films have anatase phase which is good for solar cells application. Film of La-doped TiO 2 /TiO 2 has high grain size. The optical properties like transmittance, absorbance, refractive index, extinction coefficient, dielectric constants and band gap are measured by UV–Vis spectroscopy. The film of La-doped TiO 2 /TiO 2 has low bandgap and high transmittance in visible range making it a good candidate for dye sensitized solar cells (DSSCs). DSSCs from these electrodes are prepared by using electrolyte (iodide/tri-iodide) and dye (N719). 1% La–TiO 2 /TiO 2 based cell has highest open-circuit voltage (0.74 V), Fill-Factor (0.73), short-circuit current density (6.57 mA/cm 2 ), and efficiency (3.53%) as compared to other cells. Low value of bandgap energy, weak recombination rate, improvement in charge transfer rate is mainly responsible to achieve highest efficiency rate (3.53%). • Bi-layers films of TiO 2 and La-TiO 2 are deposited by sol-gel technique. • 1% La-TiO 2 /TiO 2 film has large grain size, small E g and high transmittance in the visible region. • 1% La-TiO 2 /TiO 2 film has maximum efficiency (3.53%).

Investigating the Impact of Growth Time and Methane Flow on Graphene Synthesis using Nickel Foil

Graphene has been one of the most investigated nanomaterials in recent years due to its one atom thickness nature and its extraordinary properties such as high conductivity and excellent transmittance in visible range, bendability and high carrier mobility. Although there are many techniques to grow graphene, chemical vapor deposition technique is one of the best approach to synthesize homogeneous and commercial scale graphene in thin film form. Many parameters can affect the quality and homogeneity of the graphene film that is grown with this technique. In this study, two growth parameters which are methane flow rate and growth time were investigated to find out their effect on the quality of the graphene film, which is grown on nickel foil. Graphene film grown with different flow rates of methane (from 20 to 50 sccm) and growth time (50 to 20 mins.) were examined. We found that single layer graphene film could only be grown under 20 sccm methane flow in 20 mins. growth time as evidenced via Raman spectroscopy measurements. Furthermore, the single layer graphene film was found to be in high homogeneity as confirmed by Raman mapping. On the other hand, multi-layer graphene film was obtained by increasing both methane flow and growth time.

Flexible Transparent Heat Mirror for Thermal Applications.

Transparent heat mirrors have been attracting a great deal of interest in the last few decades due to their broad applications, which range from solar thermal convection to energy-saving. Here, we present a flexible Polyethylene terephthalate/Ag-doped Indium tin oxide/Polydimethylsiloxane (PAIP) thin film that exhibits high transmittance in visible range and low emissivity in the thermal infrared region. Experimental results show that the temperature of the sample can be as high as 108 °C, which is ~23 °C higher than that of a blackbody control sample under the same solar radiation. Without solar radiation, the temperature of the PAIP thin film is ~6 °C higher than that of ordinary fabric. The versatility of the large-area, low-radiation-loss, highly-transparent and flexible hydrophobic PAIP thin film suggest great potential for practical applications in thermal energy harvesting and manipulation.

Novel reparation method for polymethyl methacrylate optical windows of aircrafts damaged by service environment

The optical properties of polymethyl methacrylate (PMMA) with varying degrees of artificial scratches have been studied with the aim of reproducing the change of visibility of an aircraft’s PMMA optical windows after being damaged in their service environment. A novel maintenance method that can perfectly restore the optical property of PMMA has been identified and employed in the repair of the scratches that are formed on the surface of PMMA. This convenient and low-cost method entails polishing PMMA with different types of sandpaper to remove the scratches, and then spin-coating the repair solution in order to restore the optical properties of PMMA. The effect of this repair mechanism and parameters of the repair process were studied. The results indicated that the optical performance of PMMA is closely related to the mesh size of sandpaper, and improper parameter selection destroys the general effect of the repair. When the number of sandpaper mesh is low, the size of the abrasive particle is relatively larger, which can cause deeper friction marks on the surface of PMMA optical windows. Surface treatment using 5000 mesh sandpaper lowers surface roughness (Ra=0.566 nm), and optical transmittance in visible range can be restored to more than 88%.

Structural and optical band gap modification of Zn2SnO4 thin films after irradiation with swift heavy ions for transparent electrode applications

The structural changes and their effect on optical properties have been studied in Zn2SnO4 thin films irradiated by Ag9+ ions. The irradiation of thin films transforms the mixed crystal structures in to a single diffraction plane. In the XRD, the single peak is the result of atomic jump within the material due to the change in activation energy after irradiation. The XRD and SEM confirmed the modifications of lattice parameters and grains in accordance with the basic requirement of material to be used as transparent conducting oxides. In optical studies, the absorption spectra and Tauc plot confirm the neutralization of free electrons in conduction band minimum which results in an increase in the optical band gap for better transmission in visible range. The results indicate that the swift heavy ions passed from polycrystalline material synergistically with inelastic electronic energy loss to promote the formation of Zn2SnO4 oriented in a single direction and lead to rapid phase transformation.

In Vitro Culture of Human Corneal Endothelium on Non-Mulberry Silk Fibroin Films for Tissue Regeneration.

PurposeThe purpose of this study was to determine if non-mulberry varieties of silk are suitable for the culture of corneal endothelium (CE).MethodsAqueous silk fibroin derived from Philosamia ricini (PR), Antheraea assamensis (AA), and Bombyx mori (BM) were cast as approximately 15 µm films with and without pores on which human CE cells were cultured. Tensile strength, elasticity, transmittance in visible range, and degradation properties of the films were characterised. Adhesion of CE to the silk films was quantified using MTT assay in addition to quantifying the number and area of focal adhesions using paxillin. Expression of CE markers was determined at the gene and protein levels using PCR and immunostaining, respectively. Barrier integrity of the cultured cells was measured as permeability to FITC dextran (10 kDa) in the presence or absence of thrombin.ResultsThe films exhibited robust tensile strength, >95% transmittance and a refractive index comparable to the native cornea. BM degraded significantly faster when compared to PR and AA. A comparison between the three varieties of silk showed that significantly more cells were adhered to PR and AA than to BM. This was also reflected in the expression of stable focal adhesions on PR and AA, thus enabling the formation of intact monolayers of cells on these varieties unlike on BM. Treatment with thrombin significantly increased cellular permeability to dextran.ConclusionsOur data shows that PR and AA varieties sufficiently support the growth and function of CE cells. This could be attributed to the presence of natural cell binding motifs (RGD) in these varieties.Translational RelevanceDevelopment of a suitable carrier for engineering the CE to address a major clinical requirement of healthy donor tissues for transplantation.

Heat-resistant Poly(methyl methacrylate) Modified by Biomass Syringaldehyde Derivative: Preparation, Thermostability and Transparency

Poly(methyl methacrylate) (PMMA) has found a lot of practical uses, however, how to efficiently and cost-effectively improve its relatively low thermal properties remains as an intractable academic challenge. This article reports a novel strategy for improving heat-resistance of PMMA by using biomass syringaldehyde. Syringaldehyde methacrylate (SMA) was first synthesized and then used as comonomer to copolymerize with methyl methacrylate (MMA) through bulk polymerization and solution polymerization. The copolymers can be obtained in high yield and demonstrate remarkably improved heat-resistance according to differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and derivative thermogravimetry analyses (DTG). Moreover, the modified PMMA still maintains good light transmittance in visible range. The study provides a new alternative for modifying PMMA, and the modified PMMA may find new applications as heat-resistant polymeric material which cannot routinely achieved by PMMA itself. In addition, SMA as a new type of green heat-resistant modifier derived from renewable biomass syringaldehyde may have potential applications in heat-resistant modification of materials.

Simultaneous achievement of high visible transmission and near-infrared heat shielding in flexible liquid crystal-based smart windows via electrode design

Light and heat management are the two vital requirements for smart window towards ideal solar control. However, as a representative polymer dispersed liquid crystal (PDLC) device, little attention has been paid to heat management. Herein, a TiO2/Ag(Cu)/TiO2 (TCAT) electrode was designed and optimized to achieve the tunability of transmission in visible range and near-infrared heat shielding simultaneously. The continuous growth of ultrathin Ag films with low percolation threshold was achieved on TiO2 underlayer by doping a certain amount of Cu. Then the trade-off of PDLC devices’ optoelectrical properties was realized. The average ON state specular transmittance of TCAT-based PDLC devices reached 81.9%, 84.9%, 81.9% and 79.9% for Ag(Cu) thicknesses of 7 nm, 9 nm, 11 nm and 13 nm, respectively. In addition, TCAT electrodes exhibited satisfactory ratio of light to solar gain by taking visible transmittance and solar heat gain coefficient into comprehensive consideration. Compared with ITO-based PDLC counterpart, a notable temperature-decreases of 4.6 °C was observed at ON state of TCAT-based device, indicating an excellent heat shielding performance. The proposed TCAT electrode design is promising in smart window application especially for building energy conservation in hot areas or the summer season.

Different rare earth (Sm, La, Nd) doped magnetron sputtered CdO thin films for optoelectronic applications

Pure and rare earth elements of samarium (Sm), lanthanum (La) and neodymium (Nd) doped cadmium oxide (CdO) thin films were deposited on glass substrates by radiofrequency magnetron sputtering at room temperature. The influence of rare earth dopants on the microstructural, morphological and optoelectronic properties of the CdO thin films were studied elaborately. The X-ray diffraction studies revealed the polycrystalline with face centered cubic structure of CdO thin films. The structural defects were increased with increase of dopant’s ionic radii. The presence of the dopants in host CdO thin films was confirmed by X-ray photoelectron spectroscopic analysis. The roughness of the films was decreased for the doped samples and Nd doped CdO thin film has the minimum roughness value of 1.29 nm. All the films exhibited high transmittance in visible range and well pronounced Moss-Burstein shift was observed in the band gap value. Emission bands of photoluminescence spectra depicted the presence of oxygen vacancies. Hall Effect measurement showed an increase in carrier concentration and electrical conductivity of the films with the addition of dopants. The suitable combination of high conductivity (2872 Ω−1·cm−1) with optical transparency (88%) and lower surface roughness of Nd doped CdO thin film, makes it a potential candidate for the transparent conducting oxide in optoelectronic devices.

Room-temperature production of silver-nanofiber film for large-area, transparent and flexible surface electromagnetic interference shielding

A kind of pollution known as electromagnetic interference (EMI), which results from ubiquitous usage of various electronic communication and military radar equipment, has been receiving increasing attention recently. However, large-area EMI shielding on transparent and/or curved surfaces, including building windows, curved glass wall, and special requirements spaces (SRSs), remains hard to achieve. In this paper, a silver nanofiber (AgNF) based flexible and transparent EMI shielding film was successfully assembled via a room-temperature roll-to-roll production method. For transparent application scenario, AgNF with 89% transmittance in visible range and 1 μm thickness shows ~20 dB shielding efficiency (EMI SE). On the other hand, total shielding (>50 dB) is obtained when the thickness of AgNF increases to 10 μm, while its transmittance in visible range remains higher than 75%. Considering the facile and scale-free production technology, this material can be readily applied in large-scale, transparent, and/or SRSs EMI shielding.

Anti-soiling coatings for solar cell cover glass: Climate and surface properties influence

The objective of this study has been twofold: i) to investigate different strategies for CPV module glass surface modification, in particular preparing hydrophilic and hydrophobic coatings in order to reduce the dust accumulation (soiling) on the module surface; ii) to perform a joint comparative soiling testing in Italy, Spain and Brazil in order to understand the limit and advantages of the proposed anti-soiling coatings in different climate condition. Two TiO2/SiO2 films with different titanium content have been synthesized and benchmarked against pure TiO2 in relation to transparency and hydrophilicity. Moreover, a hydrophobic antireflective material based on functionalized-SiO2 thin film was also investigated. All these coatings have been deposited over low iron float glass substrates by sol-gel dip-coating and electron-beam evaporation technique. TiO2/SiO2 and functionalized-SiO2 films showed higher transmittance in visible range than pure TiO2. TiO2/SiO2 films showed a persistent superhydrophilic character with water contact angles near to 0°, while functionalized-SiO2 presented hydrophobic property. The joint comparative soiling tests showed the importance of setting anti-soiling strategies in region characterized by more dry climate: in Brazil, which during the soiling test was characterized by a long dry period, the anti-soiling coatings were effective in reducing the soiling deposition and in the removal of the contaminants by rainwater; in Spain and Italy, the more frequent rain precipitation made the soiling effect less relevant, however, the deposition of anti-soiling coating on the module cover glass allowed to fully recover the initial transmittance after rain washing. A chemical and mineral characterization of the soiling has been carried out revealing the dependence of the contaminants from the environment conditions (e.g. car traffic, presence of industries, amount of rain and local minerals in the ground).

Effect of niobium doping on the structural, electrical and optical properties of epitaxial SnO2 films on MgF2 (110) substrates by MOCVD

Niobium (Nb)-doped SnO2 films were epitaxially grown on MgF2 (110) substrates by the metal organic chemical vapor deposition (MOCVD) technique. Structural, electrical and optical properties of the obtained films with different Nb-doping levels were investigated. The X-ray diffraction analysis revealed that the obtained films were rutile structure SnO2 grown along the (110) orientation. The epitaxial relationship between the Nb-doped SnO2 film and MgF2 substrate was clarified as SnO2 (110) || MgF2 (110) with SnO2 [001] || MgF2 [001] by the interface selected area electron diffraction measurement. A Hall mobility as high as 84 cm2 V−1 s−1 with the lowest resistivity of 2.9 × 10−3 Ω cm were obtained for the 4.3 at.% Nb-doped SnO2 film. The average optical transmittance in visible range of the 4.3 at.% Nb-doped SnO2 film exceeded 80% and the optical band gap was about 4.04 eV.

Fabrication, characterization and electroluminescence studies of SrS: Ce3+ ACTFEL device

The SrS: Ce3+ thin film active phosphor layer of different thickness based alternating current thin-film electroluminescent (ACTFEL) devices are fabricated by electron beam evaporation deposition (EBED) method. The morphology and chemical composition of the deposited films are investigated by field emission scanning electron microscopy (FESEM). The optical transmittance in visible range for the optimum film and optical band gap of SrS: Ce3+ film is described on the basis of Ce3+ doping concentration.