Light Transparency Research Articles

Infrared‐Reflective Transparent Hyperbolic Metamaterials for Use in Radiative Cooling Windows

AbstractPassive multilayer coatings for windows have potential to improve energy consumption for indoor temperature regulation. The coatings should block the solar IR energy (800–2500 nm) while maintaining visible light transparency (400–700 nm) to prevent unwanted heating of the interior of a building or a vehicle. It should also efficiently radiate thermal energy to prevent excessive heating. Although solar energy management and radiative cooling techniques have been investigated individually, the combination of the two, a transparent radiative cooler, has emerged only recently. This study theoretically and experimentally demonstrates a transparent radiative cooling window using a combination of planar hyperbolic metamaterials and a uniform layer of polydimethylsiloxane, resulting in high visible transparency (>60%), IR reflectivity (>89%), and thermal emissivity (>95%). Daytime temperature experiments confirm that the cooling window efficiently lowers the interior temperature by as much as 7 °C.

Pressure Engineering Promising Transparent Oxides with Large Conductivity Enhancement and Strong Thermal Stability.

Transparent conducting oxides (TCO) with high electrical conductivity and high visible light transparency are desired for a wide range of high-impact engineering. Yet, usually, a compromise must be made between conductivity and transparency, limiting the practical application of a TCO to the next level. Furthermore, TCO performance is highly sensitive to composition, so conventional synthesis methods, such as chemical doping, cannot unravel the mysteries of the quantitative structure-performance relationship. Thus, improving the fundamental understanding or creating materials-by-design has limited success. Here, a strategy is proposed to modulate the lattice and electronic and optical properties precisely by applying pressure on a TCO. Strikingly, after compression-decompression treatment on the indium titanium oxides (ITiO), a highly transparent and metastable phase with two orders of magnitude enhancement in conductivity is synthesized from an irreversible phase transition. Moreover, this phase possesses previously unattainable filter efficiency on hazardous blue light up to 600°C, providing potential for healthcare-related applications with strong thermal stability up to 200°C. These results demonstrate that pressure engineering is a clean and effective tool for tailoring functional materials that are not achievable by other means, providing an exciting alternative property-tuning dimension in materials science.

Defects modify anisotropic saturation magnetization in transparent and flexible Hf0.95Co0.05O2 thin films for wearable device

A pure inorganic flexible magnetic thin film that is transparent with high temperature and light weight is crucial for high temperature flexible/wearable magnetic sensors and spintronics devices such as electronic skin and a mechanical arm. Here, a transparent flexible Hf0.95Co0.05O2 (HCO) thin film with various thicknesses of 105, 140, 175, and 210 nm was deposited on fluorophlogopite (F-Mica) substrates by using a sol-gel method. All of the flexible HCO samples show two phase structures with a monoclinic phase (M-phase) and an orthorhombic phase (O-phase), resulting in strain and strain relaxation in the samples of different thicknesses. An out-of-plane anisotropy behavior in saturation magnetization was observed in the flexible HCO samples, and the values of (Ms-out-of-plane−Ms-in-plane) decrease with the increase in the thickness. The content of Co2+ increases and the content of Co3+ and vacancy oxygen decrease when the thickness increases, which will affect the anisotropic magnetization behavior in the flexible HCO thin films. Moreover, the flexible HCO samples show excellent light transparency (above 80% in the visible range). The flexible HCO thin films with an anisotropic magnetization behavior and high transmittance are promising for various applications in transparent flexible/wearable devices.

Color-tuning neutrality for soluble black-to-transmissive electrochromics via solution co-processing

Chemical polymerization towards obtaining alternating copolymers ECP-B and ECP-R of the electron-acceptor (2,2′-biindoline)-3,3′-dione or benzotriazole and the electron-donor thiophene derivatives, with or without long alkyl chain substituents serving as solubilization components, was performed in advance. Electrochromic studies demonstrated that ECP-B transformed from neutral-state blue to an oxidized-state transmissive light cyan color, while ECP-R displayed a red color in the neutral state and a transparent light gray color in the oxidized state. Then, the neutral-state black polymer electrochrome (ECP-2) was obtained by blending two donor-π-acceptor (D-π-A) copolymers with complementary spectral absorption via solution co-processing in different mix ratio. The film ECP-2 in 1:2 mass ratio of ECP-R to ECP-B demonstrated a full range of visible absorption, and switched between an improved saturated black neutral state (L* = 57.3, a* = 4, b* = −7) and a light cyan transmissive oxidation state (L* = 77.6, a* = −4, b* = −5) reversibly with the moderate optical contrast of ca. 30%, the fast switching speed as low as 1.2 s, and the high coloration efficiency (222 cm2·C-1), which suggested a promising method for large area electrochromic device applications. Besides, a larger contrast (65.9%) in NIR region (1500 nm) for the ECP-2 film concomitant with an outstanding coloring efficiency (515 cm2·C-1) and a fast response time (0.6 s) were favorable for many NIR applications.

Semitransparent polymer solar cell/triboelectric nanogenerator hybrid systems: Synergistic solar and raindrop energy conversion for window-integrated applications

Development of photovoltaic (PV)-derived hybrid power systems can overcome the weather-dependent electricity production and increase the amount of dispatchable renewable energy generation. Herein, monolithic hybrid devices are developed via rational integration of high-performance semitransparent polymer solar cells (ST-PSCs) and liquid−solid triboelectric nanogenerators (TENGs). High-performance PSCs with efficiencies of 17.4% for rigid and 15.7% for flexible devices are achieved. Further electrode modifications and integration of transparent TENGs synergistically balance the above-bandgap photon harvesting and transparency in a broad wavelength range (380 − 1000 nm), yet significantly reduce the transmittance in the near-infrared wavelength range (1000 − 2500 nm) of hybrid devices. The hybrid devices simultaneously provide high visible light transparency, good color fidelity, efficient heat resistance and possibility to integrate on rigid and flexible substrates. The hybrid devices attain a high solar conversion efficiency of 10.1% under 1 sun, indicating efficient light-to-electricity conversion (a maximum electrical power output: 101 W m−2) on sunny days. The hybrid devices can also generate a maximum electrical power output of 2.62 W m−2 through waterdrop energy conversion, implying complementary green electricity production on rainy days. The controlled ambient temperature and specific transmittance windows provided by the hybrid devices sustain plant growth and highlight their great potential in agricultural applications. Gratifyingly, this work demonstrates the first example of ST-PSC/TENG hybrid systems for scaling up renewable power generation in different weather conditions, considering architectural and agricultural applications.

Water Quality Downstream of Cimanuk River, West Java

The Cimanuk River is one of the three major rivers in West Java, incidentally the second largest after the Citarum River which aims to analyze the physical and chemical qualities in the lower reaches of the Cimanuk River. The research was conducted for three months, which was carried out in the lower reaches of the Cimanuk River. Water sampling using the survey method. Sampling was carried out at three points by paying attention to community activities around the river waters. The parameters analyzed were temperature, Light Transparency, pH, TSS, TDS, DO, COD, Ammonia, Nitrate, Nitrite and Salinity Calculations following the quality standard rules of PP No. 22 of 2021, the water temperature at the three stations was 25°C. The value of light transparency ranges from 32 – 37 cm. The pH value at all three stations is neutral. The Salinity values at stations 1 and 2 are 0, and station 3 is 1.7. DO values at all three stations ranged from 7.0 – 9.6 mgL-1. COD values at all three stations ranged from 9.3 – 15 mgL-1. TDS values at all three stations range from 244 - 343 mgL-1. TSS values at all three stations ranged from 29 – 84 mgL-1. Ammonia values at all three stations ranged from 0.002 - 0.003 mgL-1. Nitrate values at all three stations ranged from 0.31 – 0.55 mgL-1. Then, the nitrite value at all three stations was 0.020 – 0.022 mgL-1. The results show that the parameters in the lower reaches of the Cimanuk River meet quality standards.

Synthesis of transparent silica microspheres with mesopores to encapsulate dye molecules for the fluorescence enhancement

Transparent mesoporous silica microspheres were successfully synthesized via sol-gel method followed by calcination. The prepared microspheres consisted of sub-micrometer particles embedded in a gel matrix, which was the main product of the fast hydrolysis and condensation of TEOS in the octylamine-containing medium. The continuous gel network gave light transparency of these microspheres. The microspheres were statically immersed in rhodamine 6 G (R6G) dye solutions with different concentrations. The guest R6G molecules loaded in the microspheres exhibited significantly enhanced fluorescence performance compared with the correspondent dye solutions. The localization and dispersion of dye molecules in the nanopores of microspheres reduced the aggregation of dye molecules which otherwise quenched the luminescence. A comparative study on the loading of the same dye within another transparent and an opaque silica gel with larger pore sizes indicated that the transparency and the smaller pore size of the transparent microspheres explained its larger fluorescence enhancement effect.

Water Quality of Cilutung River Sumedang Regency, West Java, Indonesia

Cilutung River is one of the sub-watersheds in the middle of the Cimanuk River which is located in Tomo District, Sumedang Regency. Cilutung River utilization is used for sand mining activities and may cause a negative impact on water resources, among others causing a decrease in water quality. The objective of this research effort is to determine the condition of water quality in the Cilutung River, Sumedang Regency in September - November 2020. The method used in this research is the survey method. The technique of determining the station was carried out by purposive sampling method and was carried out at three research stations. The sampling technique was carried out in situ and ex-situ. Parameters observed in situ consist of temperature, light transparency, DO, and pH and ex situ consist of TDS, TSS, nitrate, ammonia, and COD. The temperature value obtained is about 25℃ - 28,7℃. Light transparency value is about 17cm - 23cm. TDS value was about 197 mgL-1 - 276 mgL-1. TSS value was about 27 mgL-1 - 94 mgL-1. pH value is about 6.92 - 7.03. DO value was about 7.1 mgL-1- 7.4 mgL-1. Nitrate value was about 0.06 mgL-1- 0.64 mgL-1. Ammonia value was about 0.001 mgL-1 - 0.002 mgL-1. COD value was about 5.5 mgL-1- 9.6 mgL-1. In general, the water quality of the Cilutung River is classified as good and safe following the water quality standards class II for aquaculture from Regulation of The Government of The Republic of Indonesia No. 22 of 2021. However, the TSS value is above the class II threshold and close to the class III limit due to the sand mining in the Cilutung River.

Characterization and Antifungal Activity of Pullulan Edible Films Enriched with Propolis Extract for Active Packaging.

Active pullulan films with the addition of 3, 5 or 10% propolis extract produced by the casting method were tested in the study. Propolis extracts from Bochnia County, Siedlce County and Ełk County (Poland) were used. The appearance of the films was characterized, as well as physical parameters (thickness, moisture content, water solubility), tensile strength (TS), elongation at break (EB), optical characteristics (light transparency, UV barrier, color) and antifungal properties. The antifungal activity of the films was tested by the disc diffusion method against yeast (Candida albicans, C. krusei, Saccharomyces cerevisiae, Rhodotorula mucilaginosa) and mold (Alternaria solani, Fusarium solani, Rhizopus stolonifer, Colletotrichum gloeosporioides, C. cladosporioides, Aspergillus niger, A. ochraceus, Mucor mucedo, Penicillium expansum, P. chrysogenum). The origin of propolis influenced the color and water solubility of the films. The addition of increasing concentrations of propolis extract increased the film thickness and the intensity of the yellow color, extended the water dissolution time of the film and reduced the values of TS and EB. The addition of propolis extract in the pullulan film improved UV radiation protection but decreased light transparency. The antifungal activity increased significantly with the increasing concentration of propolis extract in the film, regardless of the origin of propolis. Molds showed greater sensitivity to pullulan films containing propolis extract than yeasts. In general, films made of pullulan with the addition of propolis extract can be considered as natural active packaging to protect against the growth of fungi in food.

Flexible and Semi-Transparent Silicon Solar Cells as a Power Supply to Smart Contact Lenses.

Supplying electric power to wearable IoT devices, particularly smart contact lenses (SCLs), is one of the main obstacles to widespread adoption and commercialization. In the present study, we have successfully designed, fabricated, and characterized semi-transparent, self-supported, and flexible single crystalline silicon solar cells using a single-sided micromachining procedure. Optical, mechanical, and electrical simulations, together with the practical measurements, verify the application of our developed solar cells to be mounted on a limited-footprint and flexible SCL. The 15 μm-thick silicon solar cells conformally fit on a dome-shaped contact lens (ROC = 8 mm) without any mechanical and electrical degradation. This homojunction photovoltaic device containing an array of micro-holes exhibits a V oc, J sc, and maximum power density of 504 mV, 6.48 mA cm-2, and 1.67 mW cm-2, respectively, at 25% visible light transparency under an AM1.5 one sun condition. Furthermore, the measurements were conducted under low-intensity indoor light conditions and resulted in a maximum power output of 25 and 42 μW cm-2 for the 50 and 25% transparent solar cells, respectively.

High-Performance Semitransparent Organic Solar Cells: From Competing Indexes of Transparency and Efficiency Perspectives.

Semitransparent organic solar cells (ST‐OSCs) offer potentially more opportunities in areas of self‐powered greenhouses and building‐integrated photovoltaic systems. In this work, the effort to use a combination of solution‐processable gold nanobipyramids (AuNBPs)‐based hole transporting layer and a low/high dielectric constant double layer optical coupling layer (OCL) for improving the performance of ST‐OSCs over the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT) is reported. The fabrication and characterization of the ST‐OSCs are guided, at design and analyses level, using the theoretical simulation and experimental optimization. The use of a low/high dielectric constant double layer OCL helps enhancing the visible light transparency while reflecting the near‐infrared (NIR) photons back into the photoactive layer for light harvesting. NIR absorption enhancement in the ST‐OSCs is realized through the AuNBPs‐induced localized surface plasmon resonance (LSPR). The weight ratio of the polymer donor to nonfullerene acceptor in the bulk heterojunction is adjusted to realize the maximum NIR absorption enhancement, enabled by the AuNBPs‐induced LSPR, achieving the high‐performance ST‐OSCs with a high PCE of 13.15% and a high AVT of 25.9%.

(Invited, Digital Presentation) Quantum Dots Based Transparent Light Emitting Diodes

Colloidal quantum-dot light-emitting diodes (QLEDs) have attracted considerable attention in the optoelectronic industry due to their remarkable performance, which makes them promising candidates for displays and lightning technology with a particular emphasis on color purity, brightness, and emission tunability. For these reasons over last few years a very impressive progress has been obtained in this research area in terms of improvement of QLED external quantum efficiency, their brightness and lifetime. While the race to improve the parameters of key importance for the operation of the QLED continues and QLEDs will be probably commercially available soon, the other topics related with QLED devices are at much less advanced level. This includes for example development of flexible, transparent or printable QLED devices or preparation of QLED devices in air. In this paper we will present our results related with flexible and/or transparent QLED devices obtained from green Cd-based quantum dots. We will discuss optical and electrical properties of QLED devices when using as transparent, conductive electrodes PMA/Ag, MoOx/Au/MoOx or silver metal-mesh fabricated by Ultra Precise Deposition (UPD). We will also describe thin-film deposition methods such as spin-coating/sputtering or inkjet-printing as a new versatile approach towards fabrication of flexible transparent electronics.

N-Ga2O3/p-SnS heterojunction thin-films based transparent photovoltaic device

Due to the urgent requirement of transparent photovoltaics (TPVs) for building integrated applications, solar-blind photodetectors, and high-power devices, the immediate necessity is to develop solar cells with high transparency and good photovoltaic performance. The wide bandgap Ga2O3 has attracted significant attention for its excellent optoelectrical properties; however, the role of Ga2O3 in inorganic TPV is least explored yet. The wide bandgap Ga2O3 may give the device high optical transmittance in the UV to the NIR region by absorbing harmful UV radiations. Herein, we propose and study a novel, eco-friendly sputter-grown p-n heterojunction thin-films device by utilizing n-Ga2O3 and p-SnS for TPVs applications. The Ga2O3/SnS heterojunction device is tested for the transparent light harvester, and its photovoltaic performance is improved using variation in Ga2O3 layer thickness. All fabricated devices demonstrated optical transmittance of ~70 ± 2 % in the near-infrared (NIR) region and ~50 ± 2 % in the visible light region. By optimizing the layer thickness of Ga2O3 thin-film, the Ga2O3/SnS heterojunction quality was significantly improved and achieved a high photocurrent density of 1.15 mA/cm2 and the open-circuit voltage of 527 mV. Our fabricated device showed a power conversion efficiency of 2.9 % under UV light illumination. Furthermore, the proposed transparent photoelectric device exhibited an excellent photovoltaic effect, confirming the potential applications of the Ga2O3/SnS heterojunction for advanced optoelectronics.

Luminescent inorganic mixed borate phosphors materials for lighting

The need of new materials with desirable optical properties has become important in recent years. In particular, a need has emerged for compounds having better luminescence properties in various practical applications. The introduction of rare earth ions as activators improves the luminescence properties of the compounds considerably. Boron is one of the most abundant elements in nature. It readily combines with almost all other elements. In combination with oxygen; it forms borates comprised of various anions such as BO3 3- , B2 O5 4- , etc. Apart from these simple borates, several complex compositions exist involving mixed anions as well as double metal borates, due to the three-fold, or four-fold coordination of borate atoms. Borates intrinsically possesses characteristics that are advantageous for optical materials, which include a wide transparency range, large electronic band gap, good thermal and chemical stability, low preparative temperature, optical stability with good nonlinear characteristics, and an exceptionally high optical damage threshold. The unique crystal structure of borates determines their enhanced ultraviolet light transparency, good nonlinearity, and relatively high resistance against laser-induced damage. Some of these complex borates have interesting luminescence properties that are covered in this review. These include double borates containing rare earths RM3 (BO3 )4 , pentaborates LaMgB5 O10 , M3 R2 (BO3 )4 , where M is an alkaline earth, mixed anion borates such as aluminoborate SrAl2 B2 O7 , silicate-borates such as pekovite, SrB2 Si2 O8 , haloborates, M2 B5 O9 X, where M is an alkaline earth and X is a halogen, phosphate borates, and MBPO5 , where M is an alkaline earth. Phosphors based on these compositions find use in various applications such as fluorescence lamps, colour TVs, plasma display panels, high-intensity discharge lamps based on xenon, optically pumped solid-state lasers, eye-safe lasers, and X-ray imaging.

(Invited, Digital Presentation) Quantum Dots Based Transparent Light Emitting Diodes

Open-air fabrication of printable transparent and flexible devices is of great importance for the development of the optoelectronic industry. Colloidal quantum-dot light-emitting diodes (QLEDs) have recently emerged as promising candidates for displays and lightning technology due to their remarkable performance including high efficiency, brightness, and stability. However, the fabrication of flexible and transparent QLEDs using solution-based techniques is still poorly explored. In this paper, we describe high-quality thin-film transparent conductive electrodes (TCEs) based on dielectric/metal/dielectric (DMD) multilayer fabricated using spin-coating/sputtering method and Ag-mesh electrodes fabricated by Ultra Precise Deposition (UPD). We present flexible and transparent QLEDs based on green-emitting Cd-based quantum dots using previously optimized TCEs. We also compare both deposition techniques, discuss their advantages, and predict their potential impact on the development of the optoelectronic industry.

Improving broadband absorption and transparent properties for microwave metamaterial via stimulating bimodal effect with induced water substrate

In this paper, a frequency selective microwave absorber is designed and demonstrated with water as the substrate layer, which realizes >90% absorption in the frequency range of 7.3–20 GHz and 73.6% light transparent in the spectrum range of 400–800 nm. The improved absorption is believed to be attributed to the synergy between the intrinsic resonance of the ITO metasurface and the new resonance excited by the substrate water layer. Particularly, the light transparence of the absorber is improved with the introduced water layer. Therefore, the proposed absorber shows excellent comprehensive performances for high optical transparent microwave broadband absorbers.

Synthesis and reactivity of novel cinnamonitrile derivatives as reactive UV stabilizers for enhanced light protection and performance of coatings

Ultraviolet (UV) light is generally harmful to human health and organic compounds (for example, plastics) as it deteriorates the long-term stability via photodegradation. Thus, an efficient strategy for reducing light-induced damage is the key to maximizing the operation lifetime or durability of materials. The most common means of preventing UV light-induced damage is by adding compounds that possess excellent UV absorbing capability. In this study, novel cinnamonitrile derivatives were designed and synthesized for their application as UV absorbers in pressure-sensitive adhesives. Absorption wavelengths were finely tuned by simple structural modification, and better molar absorptivity was obtained. The hydroxyhexyl functional group affixed into the cinnamonitrile core granted superior solubility (>10 wt%) in common organic solvents and acrylic monomers/resins, instigating enhanced UV blocking and visible light transparency. Further, to enhance the solubility and long-term stability of UV absorbers within a network, hydroxyhexyl-functionalized cinnamonitrile UV absorber was incorporated into urethane-based crosslinkers. Covalently attached reactive UV absorbers improved the adhesion property even at a high loading of UV absorber and remarkable physical persistence within the network.

Computed Origami Tomography

In this paper, we provide assembly instructions for an easy-to-build experimental setup in order to gain practical experience with tomography. As such, this paper can be seen as a complementary work to excellent undergraduate-level mathematical textbooks concerned with the basic mathematical principles of tomography. Since the setup uses light for tomographic imaging, the objects investigated need to be light transparent, such as origami figures. Should the reader want to experiment with computational tomographic reconstructions without assembling the device, we provide a database of several objects together with their tomographic measurements and publicly available software. Moreover, recent advances in cryo-imaging have enabled three-dimensional high-resolution visualization of single particles such as, for instance, viruses. To exemplify, and demonstrate, single particle cryo-electron microscopy, we provide an advanced assembly that we use to generate data simulating a cryo-recording. We also discuss some of the major practical difficulties in reconstructing particles from cryo-microscopic data.

Facile preparation of lignin-containing cellulose nanofibrils from sugarcane bagasse by mild soda-oxygen pulping

Lignin-containing cellulose nanofibrils (LCNFs) with tunable lignin contents from sugarcane bagasse were directly prepared by low-temperature soda‑oxygen pulping combined with simple mechanical treatment. The residual lignin structure, morphology and physical dimensions of LCNFs, and properties of the relevant cellulose nanopapers (CNPs) were investigated. In situ 2D Heteronuclear Single Quantum Coherence (HSQC) NMR spectra showed β–O–4 linkages, ferulate, and para-coumarate were well preserved in the LCNFs. Compared with the cellulose nanofibrils (CNFs), LCNFs displayed a more uniform size and narrow diameter distribution. The corresponding CNPs exhibited outstanding mechanical properties (tensile strength reached 152.9 MPa), and excellent combined optical properties both in the UV blocking and visible light transparency. Moreover, the water contact angles (50.0–80.2°) of LCNFs were much higher than that of CNFs (21.7°). Direct preparation of LCNFs under mild condition would unlock the full potential of cellulosic materials and provide enhanced opportunities for cellulose to fabricate multi-functional and high-value materials.

Calculation of the Moment of the Beginning of the Existence of Light in the Universe

The apparent age of the universe is about T » 13.56´109 years. Light is part of our everyday life, but it has not always existed. According to physicists, it began to exist about ~360 000 to 380 000 years after the Big Bang. 
 
 We calculated the exact moment of the appearance of light based on a new cosmological model shown in 2019. In this model, we make the following hypotheses: 1) The apparent radius of curvature of the universe increases at the velocity of light. 2) Our universe is in rotation on itself. 3) The tangential speed of the universe’s periphery is the same as an electron. 4) Our universe is made of a ″material universe″ imbricated in a ″luminous universe″. 
 
 With Einstein’s laws of relativity for spinning disks and the addition of speeds, we can establish the moment where the universe became transparent and emitted light. We evaluate that moment to ~361 108 years after the Big Bang.
 
 The assumptions used for the calculations reveal some interesting facts about the structure and characteristics of our universe. This article may be a step-stone for other analyses.